Tom Hand's detailed guide to the Torqueflite automatic transmission
Courtesy of the Walter P. Chrysler Club with our most sincere thanks. First published in 1983. Click here for our TorqueFlite overview / main page.
Part 1: overview and what each part does
This is part one of a three part paper. The first part explains the individual units of the Torqueflite automatic transmission. I've supplied a simplified block diagram for each gear range to show what units are actually working. The second part deals with modifications and justifications as well as the advantages and disadvantages of altering the Torqueflite shift qualities. Part three give some of the techniques that can be used to troubleshoot Torqueflite irregularities that I've seen most often. All three sections, when taken as a whole, should give an overall view of the Chrysler Torqueflite Automatic Transmission.
I have written this to serve three purposes:
- To familiarize Chrysler products owners with the components and operation of 727 and 904 Torqueflite transmissions.
- To explain and justify modifications of stock Torqueflites.
- To give basic trouble shooting techniques.
This article is not intended to give specifics about every Torqueflite made. If you are interested in more detail than I have given, order: Automatic Transmission Manual: TM-508 from the Chrysler Training Division. This will explain just about everything you would want to know about 1966 and later Torqueflite 904s and 727s. As in any repair situation, a person should refer to the appropriate Chrysler service manual for exact details and adjustments of particular units.
The photographs included with this article are of a 1976 727-A that I built for a police car (I spent a lot of time cleaning this unit and at the same time, learning that washing parts in a dishwasher works but tends to rust them). The 904 is different in some regards but I didn't have one available for photographs. Therefore, I will explain construction and operation of both 904s and 727s where the differences are of concern to adjustments and/or assembly procedures.
Many thanks to David Frey, Vicki Milley, Debbie Hoflo, and a very special thank you to Tom Mallot for his photographic help.
Torqueflites first appeared in 1956, as an option, in Imperials and 300Bs. This unit had a cast iron body with an aluminum converter housing and aluminum tail shaft housing. The gear ratios were the same in the forward gears as they are now; 2.45:1 first gear, 1.45:1 second gear, and 1.00:1 direct or third gear. Reverse was 2.21:1 in the early units and 2.20:1 in all models since 1962. These transmissions were coded A-488s and were offered standard on 1957 Imperials and other Chrysler models. In fact, the 1957 Torqueflite was heralded as "the best automatic in the world."
In 1962 the aluminum case was introduced. It had the code name of "727" and together with the torque converter, it weighed about 160 pounds. The original 727 was basically unchanged through 1965. Certain items were altered in the 1965 model year and these included enlarging of the torque converter splines on some 1965 models, elimination of their flanged output shaft, and changing the shift mechanism from two cables to one rod-and-lever arrangement. All of these changes have been incorporated on 904s and 727s since 1966.
Modifications made since 1966 have basically been small and related to longevity and driver comfort. 1971 saw introduction of the wider front clutch bushing that eliminated premature ring and drum wear. This is the modification I consider to be the best as far as high performance application is concerned.
Introduction to the TorqueFlite
The automatic transmission is a convenience item for most people. The shift lever is moved to get the car in motion and then left alone until the car is stopped. No clutch pedal to push or shifter to change between three, four, or even five forward gears makes for a minimum of driver effort. Not only were automatics originally used for general driving comfort, but they quickly found a place in competition vehicles.
The 1960s were a time that Chrysler products dominated various drag strip classes, both AHRA and NHRA. The majority of the cars were running manual transmissions as they were faster and easier to repair. However, the shock of 4000 to 6000 rpm drops on the starting line created enormous loads on tires and various driveline components. If it wasn't for the fact that tires were a lot slicker then, there probably would have been an incredible amount of additional parts breakage.
Chrysler was the first to develop better racing automatics since they already had the most dependable automatic transmissions on the road. It took G.M. until 1964 to develop the famous Turbo-Hydramatic 400. Up to that point in time, there was only the Powerglide being used seriously in G.M. racing vehicles.
The advent of the aluminum torqueflite revealed many more classes that Chrysler could dominate. Evidently, early engineering groups at Power Train Design did their homework because the original design has changed little as Chryslers still dominate A through D stock automatic in NHRA classes.With bracket racing coming alive in the 1970s, it has been almost mandatory to have a good automatic in 90% of the classes if you want to be consistent and win races. Torqueflites still fulfill the needs of Chrysler racers.
Automatics have always been four to six percent less efficient than manual transmissions. Torque converter slippage was a big contributing factor to this inefficiency; in 1978 lock-up clutch-type converters were used with Torqueflites, to help reduce the gas mileage difference between automatic and manual transmissions. I will not go into much detail on these because they are very similar in design to stock 727s and 904s with the addition of a few control valves and a slightly different torque converter.
As gas mileage demands increased, thereby decreasing engine size, Chrysler changed from 727s to use of more 904-type transmissions (G.M. created the Turbo 200-type automatic for smaller vehicles, and what a money maker this has been for automatic transmission repair shops!). No real problems were noted by changing to the smaller unit except for 1978 early lock-up shuddering. This was remedied by delaying the lock-up speed a few mph later that model year.
The Torque Converter
There has to be something to transfer motion from the engine to the transmission and that item is a Torque Converter. This unit does what its name implies; it converts or "multiplies" engine torque at low speeds and couples the engine to the drive train hydraulically at higher speeds. The converter consists of three elements, all necessary for proper transmittal of motion. The Impeller and Turbine transfer fluid between each other to drive the Input Shaft of the transmission. The Stator is a device used in the converter to multiply torque by giving proper direction to the fluid flowing between the impeller and turbine. The converter hub has slots that engage the tabs on the inner rotor of the oil pump to create oil pressure and oil flow from the pump while the engine is running.
The overall purpose of the torque converter is to:
- Provide a coupling between the engine and transmission
- Supply a method of driving the transmission oil pump
- Provide a unit that incorporates a flywheel for starting
- Supply a multiplication of engine torque of approximately 2.2:1 at low speeds and 1:1 at higher speeds
Refer to either Chrysler literature or other applicable information for more details about the internal "Vortex, Rotary and Turbulent" flow of fluid if you are interested in more of the converter operation and design. Converter diameters and stall speeds will be discussed in the modification section.
Torqueflite Exploded View
Before going into details of each subassembly in the Torqueflite, refer to the supplies photo of the exploded view of a complete 1976-727 transmission. The over-running Clutch is not shown and the Valve Body is not a 1976 model but actually a 1970 model. There are reasons for this but they are not important to the overall explanation of the internal operations. From top left you will see the Pan, the Case, and the Tail shaft, or Extension Housing and associated hardware. The top right corner contains all the Servos, Bands, Operating levers and pins, and the Accumulator and its spring. The next row has the Oil Pump and the Front Clutch assembly shown. Row three displays the Rear Clutch assembly. The fourth row holds both Planetary Gear sets, the Front Clutch hub, Sun Gear and Sun Gear Driving Shell, and the Low-Reverse Drum assembly. To the far right is the oil filter and "Direct Connection" oil filter extension. This extension is used with the deep oil pan shown in the upper left corner. The last row contains the Output Shaft, Governor Assembly and the Output Shaft Support Bearing. To the right of this is the "Brain" of the transmission; the Valve Body.
I will explain the pictures of the various units in the general order they are displayed and tell what functions the pieces have in the overall transmission operation in the following text.
Torqueflite Case Assembly
Shown is a 727 case and associated pieces (the 904 is almost identical except the size and shape of everything is slightly reduced). This case is 727-A which fits all small blocks. The 727 can also be a 727-B which fits the big blocks, or 727-RG which bolts to the six-cylinder blocks. The 904 comes in a 904-A, 904-RG, as well as units for some of the earlier 4-cylinders. Some higher performance 904 units were designated as 998s and 999s in the later 1970s.
The case is in the upper left corner. Below it are the cooler line fittings, the shifter shaft seal, and neutral start switch. The neutral start switch performs a couple of functions. It allows the engine to be started when the transmission is in only park or neutral range and it controls the electrical current to the reverse lights when the transmission is in reverse gear (This type of neutral switch has been used since 1969. 1968 and earlier cars had the reverse lights controlled from a switch on the steering column or console shifter).
Next is the case-to-tail shaft gasket and the governor support. The governor support bolts to the case and it has a threefold purpose. It supports the low-reverse drum, the governor-output shaft assembly, and it directs oil to and from the rotating governor weights (The governor works with the throttle pressure circuit to control shift points). Next is the tail shaft housing that contains the parking gear lever (used to lock the governor-output shaft assembly in park) and the output shaft support bearing snap ring. A seal is used at the end of the housing to ride on the drive shaft yoke to keep oil contained in the case.
Below all this is the oil pan (I've shown the Direct Connection deep pan with a drain plug). Its purpose is to act as a fluid source for the hydraulic system (some oil cooling is also done by the pan). Not shown is the tiller tube and the dipstick that allow the transmission fluid to be filled and have the fluid level checked from the engine compartment.
Servos and Bands
Shown in this photo are the bands necessary to give second gear (kickdown band), and reverse or manual low (low-reverse band). Here's a description of the individual parts: in the upper left corner is the low-reverse band assembly consisting of the retaining snap ring, the spring retainer, the large diameter return spring, the piston plug, the piston plug spring, the piston itself, the synthetic rubber piston seal, and the snap ring that holds the piston plug and spring to the piston.
Moving to the top of the photo again, is the low-reverse lever assembly, its adjustment screw and lock nut, the pin that the lever assembly pivots on and the rectangular strut that applies the low-reverse band. Right below the band is the anchor that holds the band when the piston pushes the low-reverse lever.
An accumulator spring, a cast iron sealing ring, the accumulator piston and one more sealing ring are displayed in the center of the photo. Both 904 and 727 Torqueflites use the accumulator to give a cushioned drive breakaway only, depending on which side of the piston the spring is placed.
In the right half of this picture is the kickdown servo assembly, and the kickdown band. The kickdown servo assembly consists of the retaining snap ring, cast iron seal ring, the aluminum pin guide, the large servo return spring, and a controlled-load servo with its cast iron rings below it.
This particular servo piston is called a controlled load servo and its purpose is to cushion the three-two downshift. The other type of servo assembly does not use an internal spring-piston assembly and it is usually found in high performance applications where soft shifts would be detrimental. Individual pieces cannot be interchanged between the standard and controlled-load servos. The apply lever at the lower right corner comes in different ratios, again depending on engine usage. Usually the higher performance transmissions use a 3.8 to 5.0 ratio lever. The higher numbered levers multiply the apply force more to tighten the band quicker and harder around the front clutch retainer drum.
The 904 uses two different types of low-reverse bands. One type is called a double wrap band, very similar to the Hemi kickdown band, and it is used with the VS engines to give greater low-reverse drum holding capability. The other band is a single width band that has less torque holding capacity and is used with six-cylinder engines. The 727 also uses a single width low-reverse band and it is used with all engines.
The low-reverse band works with the over-running clutch (which I've not shown) to hold the low-reverse drum during manual low. The 904 has a smaller over running clutch so it depends on the band to give it sufficient holding power to prevent breakage of the clutch. I'll explain later why the low-reverse drum must be held stationary, but for now bear in mind that the drum needs to be held during manual low, drive breakaway (or low) and reverse. The over-running clutch is like a stator in the torque converter, but its outer race is firmly affixed to the rear of the case whereas the outer race of the converter stator is free to lock-up or spin depending upon engine-vehicle speed difference.
The 904 uses different kickdown bands to hold the front clutch retainer drum during second gear. Most 904s have a single width band, but some 998 and 999 versions of the 904 have a drum
with five clutches, and need a wider band to hold it. Some 904s use what is called a "flex band" that performs identical functions to the standard cast band but will not retain the circular shape of the cast band when it is removed from the transmission. 727 trans-missions also use the flex band in later model years. A double wrap band (also called the Hemi or 440-6 pack band) was used with the five clutch retainer drums that were used in the maximum performance 727s. This band was wider and could produce much greater holding power than the single width cast or flex band found on most other 727 units. One might think it wise to use the Hemi-band with the standard 727 drums but it will not work because of the width difference between the four and five clutch drums. I will explain various tricks that can be done with bands, apply levers and drums in the modification section.
Oil Pump Assembly
The oil pump provides the hydraulic pressure needed to operate the various units in the transmission. It is made up of the pump body, two rotors, and the reaction shaft support. The first rotor has 14 external teeth and the second rotor has 15 internal teeth, The rotor with external teeth is driven by the torque converter hub and it meshes with the other rotor at only a few locations thereby creating a gap. As the rotor spins, fluid is picked up in this gap and is forced out where the teeth are meshing creating pressure to drive the fluid through various passageways of the pump body (The 904 pump is physically smaller and the pump body and reaction shaft support each make up one-half of the pump body assembly).
The reaction shaft holds the stator stationary in the torque converter and it supports the input shaft in its I.D. and the front clutch retainer on its O.D. The front clutch is sealed to the reaction shaft by the two cast iron rings that direct oil from the pump to the inside of the front clutch.
The oil pump body has a bushing to support the converter hub and a seal to prevent fluid leakage around it. The reaction shaft has a bushing in it to support the input shaft (which is part of the rear clutch assembly), oil pump assembly.
Pressure forces the lip seals against their surfaces and pushes the piston away from the clutch hub and applies force to the clutch pack through the Belleville spring-pressure plate assembly.
The rear clutch has to hold a larger torque load than the front clutch so the Belleville washer is used to multiply the apply force of the piston. The Belleville washer also acts as a spring to return the piston when the clutch is not hydraulically functioning. Once the plates and discs are locked in the rear clutch assembly, power can be transmitted through the input shaft, to the locked clutch-pack and to the front annulus gear (see planetary assembly photo). Once the planetaries are utilized, you get gear reduction and torque multiplication; or in other words, first or second gear depending on planetary usage.
Something not mentioned previously, but that is found in both the front and rear clutch is the check ball in the apply piston. This is not easily seen in the photos but it serves an important purpose. When the clutch is spinning but not hydraulically operating, residual fluid can be forcing the piston out against the pressure plate (front clutch) or Belleville washer (rear clutch) creating clutch drag. This ball-check valve lets that fluid (that is under pressure from the clutch assembly spinning and throwing the fluid out due to centrifugal force) out of the clutch cylinder or drum. The 904 rear clutch is smaller but operates identically to the 727. The notable difference is the front clutch hub-rear clutch retainer is two separate pieces in the 727 but they are only one in the 904.
Planetaries, Output Shaft, and Governor
I've grouped basically three separate assemblies in this one photo. The planetaries and sun gear in the top row give the various gear reductions and reversals; the output shaft transfers output torque; and the governor controls the shift points. Listed here are the planetary parts: The snap ring that holds the planetaries on the output shaft, the front planetary gear, a thrust washer, the front annulus gear, another thrust washer, the sun gear-driving shell assembly, another thrust washer, the rear planetary gear, a thin thrust washer and the rear annulus gear. The last three pieces are contained in the low-reverse drum. The front annulus gear is splined to the rear clutch discs and it drives the front planetary. Depending on gear selection, the sun gear-driving shell assembly will be driven by the front or rear clutch packs and will transmit torque to the rear planetary assembly. The four thrust washers shown are needed to prevent wear between the various rotating members.
The output shaft is shown with its thrust washer on the left. This thrust washer prevents wear between the input shaft and the output shaft. It is fiber or bronze, depending on the year of the transmission. The output shaft has four sets of splines cut into it. The splines on the left fit into the front planetary gear, while the second set locks the output shaft to the rear annulus gear and the third set holds the governor-park pawl assembly on the shaft. The splines on the far right are used to connect the drive shaft yoke solidly but still allow it to slide easily on the output shaft. The shaft also has gear teeth cut into it to drive the various size speedometer gears. In the lower right portion of the picture is the governor assembly and the output shaft support bearing with their associated snap rings. The bearing supports the loads imposed on the output shaft by the internal mechanisms of the transmission, and maintains the correct end play in the gear train.
The governor works with the throttle pressure rod to control shift points, according to the vehicle speed and engine torque requirements. Two cast iron sealing rings, the governor body-park pawl assembly and the governor valve-governor weight assembly all work together to send the governor signal to the valve body to tell it to operate various shift valves, controlling up and down shifts. There is one snap ring used to hold the governor body park pawl assembly secure on the splines on the output shaft.
As in the other units, the 904 planetarys, output shaft, and governor assembly are similar to the 727 pieces, but smaller in size. Depending on the size, both will have three or four planet pinion gears in the assembly. The four pinions will be found in higher performance units.
Control Valve Body and Filter
The valve body can be considered the brain of the transmission. It takes hydraulic signals and combines these with fluid pressure to correctly time and control all transmission functions. The springs and valves work together to modulate fluid pressure to time application of the bands and clutches. The channels that resemble endless mazes transfer fluid from valve to valve, or from valve to case passageway.
The 904 valve body will interchange with a 727 valve body if one hole in the transfer plate is elongated. Some 727s have different valves and springs than 904s but operation is similar. The lockup units have another section added to control converter clutch lockup but everything else is similar.
The valve bodies are extremely well designed, and it is hard to make a mistake while assembling them. As long as the springs are not interchanged or the balls mixed up, they always seem to work. Comparing Chrysler valve bodies with Ford units is like comparing 426 Hemis with flathead Fords, no comparison can be found. GM units are pretty slick but not as much fun to work on.
The Torqueflite in Operation
After reviewing all the previous information to get an idea what the various assemblies look like and do, the Torqueflite can now be studied as a complete unit. I'll go through a gear by gear description explaining the active components and how they combine to get the different gears. Because of the skill and generosity of a close friend, I'm able to supply a block diagram of the Torqueflite in the various gears. I've combined neutral and park on one diagram as they are very similar in operation.
Park and Neutral
Neutral and Park are very similar in the Torqueflite. No hydraulic units are operating and, with no clutches or bands applied, the input shaft-front clutch hub assembly and the driving discs in the rear clutch pack are rotating at engine speed. The rear clutch driving discs that are splined to the front annulus gear are free to spin, and the annulus gear is stationary. Therefore, all power flow stops at the rear clutch retainer.
Mechanically there is a slight difference between neutral and park inside the transmission. Something has to lock the output shaft solid to prevent unwanted vehicle motion. This is done by a piece of linkage that connects to the parking gear lever and the valve body manual gear lever. This parking gear lever is pushed into the parking gear-governor assembly by a cam on the parking linkage. The parking gear-governor assembly is splined to the output shaft so when the gear is stopped, the output shaft is stopped.
There is also a hydraulic difference between neutral and park. This is due to "intentionally" reduced line pressure. The "park" location of the manual valve (inside the valve body) allows fluid to leak by a land off the valve thereby creating a line pressure drop. This low pressure in park keeps the converter from completely filling and loading the engine unnecessarily.
In neutral, the converter is filled and there are no "controlled leaks," as in park. This is the reason Torqueflites should always have the level checked only in neutral. If you check the level in park, the level checks higher than it really is.
Control Valve Body and Filter
As mentioned earlier in the text, the valve body can be considered the "Brain" of the transmission. It takes the hydraulic signals from the governor, throttle pressure rod, and manual shift valve, and combines these with fluid pressure from the oil pump to correctly time and control all transmission functions.
I am not going to describe each valve or spring just yet. I'll incorporate that into the modification section. For now, I'll just point out that the filter and filter extension are at the top, the valve body and associated valves, springs, balls, and end plates are on the left, the separator plate is found in the right-center and the transfer plate is at the right.
The springs and valves work together to correctly modulate the fluid pressure to time application of the appropriate bands and clutches. The channels in both valve body and transfer plate that resemble endless mazes, transfer fluid from valve to valve, or valve to case passageway.
The 904 valve body will interchange with a 727 valve body if one hole in the transfer plate is elongated. Some 727s have different valves and springs than 904s but operation is similar. The lock-up units have another section added to the basic valve body to control converter clutch lock-up but everything else is similar to the standard automatic transmissions.
The Torqueflite valve bodies are extremely well designed. I like to work on them as it is very hard to make a mistake while assembling them. As long as the springs are not interchanged or the balls mixed up, they always seem to work. Comparing Chrysler valve bodies with Ford units is like comparing 426 Hemis with flathead Fords; no comparison can be found. GM units are pretty slick but not as much fun to work on.
Sometimes Chrysler owners complain of delayed motion of the vehicle after dropping it in gear from park. This is due to the converter not being fully charged in park. The best remedy for this is to start the vehicle in park and then immediately shift to neutral. This will fill the converter which gives a quicker vehicle response.
The block diagram (1) has the converter and pump shaded to show they are the only units in operation. In park, the driveline will be locked as explained above.
Drive breakaway (or low gear) is used to move the vehicle from a dead stop or very slow roll.
When the shift lever is placed in drive, the rear clutch drive plates rotate the front annulus gear pinions which then spin the sun gear in a reverse direction. The sun gear then rotates the pinion gears of the rear planetary in the same direction as the engine which gives a 2.45:1 gear reduction. The rear planet carrier is splined to the low-reverse drum which is held stationary by the over running clutch. The rear annulus gear is locked to the output shaft, so when the rear planets are rotating, the output shaft is spinning. Reviewing the mechanics of this again will show that the planet pinions of both planetaries transfer the torque from the input shaft to the output shaft. As the input shaft turns 2.45 times, the output shaft turns once.
In drive breakaway, the rear clutch is applied and line pressure is directed to various valves in the valve body. The same oil is also present at the governor and the signal is modulated and returned to the valve body to prepare for the 1-2 shift.
Manual Low, Drive Second or Manual Second
When the selector lever is placed in the low gear position something else is needed to supplement the existing Drive Breakaway units. Manual low is used to slow the vehicle down when the vehicle is in motion or to hold the transmission in low gear longer than the governor and throttle pressure circuit normally allow. Engine braking (the slowing of the vehicle) is accomplished by using the low-reverse servo to apply the low-reverse band around the drum. When the vehicle is stationary, the over-running clutch will hold the drum, but when the vehicle is already out of low gear, the drum is free wheeling and can only be stopped by the low-reverse band. (Low gear is a combination of the front and rear planetary sets, so the low-reverse drum has to be stationary to hold the rear planet carrier).
It can be seen that manual low is identical to Drive Breakaway with the addition of the low-reverse servo-band assembly and the blocking of the governor signal to the 1-2 shift valve.
The Torqueflite is shifted automatically into second gear by a governor signal pushing the 1-2 shift valve over and allowing line pressure to be directed to the front servo-kickdown band assembly and to the accumulator. The governor signal is generated by the rotation of the output shaft which throws the governor weights outward and sets up the proper pre-determined pressure (I'll go into more of the pressure relationships in the modification section). Governor pressure is also directed to the 2-3 valve in preparation for that shift.
Since the rear clutch is functioning, and the kickdown band had now been applied, the front clutch drum has now been stopped. The drum is interlocked to the sun gear driving shell with tabs that engage slots in the shell. The rear clutch is still rotating the annulus gear and the sun gear is stopped so no torque is transmitted to the rear planetary. With the sun gear held and the annulus rotating, the planet carrier is spinning at a reduced speed. The planet carrier is splined to the output shaft so it, too, rotates at a reduced speed which is 1 turn for every 1.45 turns of the input shaft.
Drive Second or Manual Second
Manual second is exactly the same mechanically as Drive second but there is a hydraulic difference. With the lever in second, the vehicle starts in low and shifts to second but line pressure blocks the 2-3 shift valve in the valve body to prevent any 2-3 upshift. The governor pressure will never overcome the line pressure on the 2-3 valve until the transmission is shifted into drive. All the same units are operating when the transmission is downshifted from drive into second. The transmission cannot upshift until the lever is moved back into Drive because the 2-3 shift valve is being blocked by line pressure.
While the transmission is in second gear, governor pressure is present on the 2-3 shift valve, the front clutch retainer is stopped by the kickdown band, and the rear clutch is applied turning the front planetary and, therefore, the output shaft. When the governor signal moves the 2-3 shift valve, fluid is applied to the release side of the front servo and the front clutch is applied. With the band released, the front clutch starts spinning. Now torque is applied to the front annulus gear by the rear clutch and torque is also applied to the sun gear driving shell by the front clutch (The driving shell is attached to the sun gear). When the sun gear and the front annulus gear spin at the same speed the planet carrier has to rotate at that speed (Gear train rules dictate that when two members of the same gear rotate at the same speed, the whole gear set rotates at that speed). Remember that this planet carrier is splined to the output shaft so it, too, turns at engine speed. Direct Drive is named for the fact that engine speed is transferred directly in a 1:1 ratio through the transmission.
When the Torqueflite is shifted into reverse a couple of interesting things happen. First the rear clutch, used in all forward gears, is deactivated. Then the front clutch is applied which locks on to the front clutch hub-input shaft assembly. Along with application of the front clutch, fluid is directed to the low-reverse servo which locks the low-reverse band tightly around the low-reverse drum-rear planet carrier assembly. Engine torque can now be transferred through the transmission.
Looking at this in order, it happens like this:
The front clutch is applied transferring engine torque through the sun gear driving shell, driving the sun gear in the same direction as the engine. With the low-reverse band holding the rear planet carrier stationary, torque is transmitted only through the planet pinions (via the sun gear) driving them in a reverse direction. The only thing left to spin is the rear annulus gear which is splined to the output shaft. Using this planetary only gives one turn to the output shaft for every 2.2 turns of the input shaft, again remembering the output rotates the opposite direction of the input shaft.
Hydraulically, there are also a couple of interesting things to note. Governor pressure will not be used in reverse and a quick line pressure check shows reverse to have about 250 + or - 20 psi (where normal line pressure is 75+ or - 19 psi). This is not immediately obvious why reverse should be so high until the rear clutch and front clutch are compared.
The rear clutch is on in all forward gears. It uses a Bellevifle spring washer to multiply the piston apply force the necessary amount to transmit engine torque through the rear clutch pack. However, the front clutch has no multiplication factor to depend on when it is applied. Since direct drive is the only other time the front clutch is used and the vehicle is already in motion, no extra holding power is needed to sufficiently lock the front clutch drum. But going into reverse, the vehicle is stationary, and much greater torque (2.2 times as much) will be transmitted through the front clutch plates. Therefore, through a couple of hydraulic tricks, line pressure is almost tripled to give the front clutch the necessary holding power.
Part two by Tom Hand - modification
This is the second part of a three part series devoted to the Chrysler Torqueflite Automatic Transmission. I'll give the reasons that I modify Torqueflites and why the majority of 904s and 727s can benefit from a few well proven alterations. Advantages and disadvantages to modifications will be explained. There are many types of kits made to improve Torqueflite and I'll give my recommendations on the ones I'm familiar with. Prices of kits and recommended usage will he discussed."
Of part one of this series has been read, it will probably be bringing up a few questions as to why a Torqueflite could be so well designed yet still need modifications. Alterations to any original design do not necessarily make that design bad; it just shows that some individuals like things to be different in one way or another.
Prior to learning the Torqueflite's internal operation and configuration, I was reluctant to tamper with originality. To overcome this reluctance and to learn at the same time, I got a spare valve body from a salvage transmission and followed the Chrysler service manual in disassembly and reassembly procedures. After I determined that the valve body was operational and was a suitable substitute for the one in my car, I performed all my modifications. This was an easy way to eliminate worries in case the valve body functioned incorrectly. The old unit could always be put back into service while the discrepancy was corrected.
I will present information that applies to both the 904 and the 727 (Most front wheel drive vehicles are not used for heavy duty purposes or racing as of yet so not much has been written on them). The information I'll give comes from my past experience and selected other references.
Reasons for Modifications
Stock Torqueflites, since the very beginning, have been very reliable. In a vehicle's lifetime with normal operations, little, if any, maintenance was needed. The trucks and high performance cars were equipped with stronger, harder shifting automatics; the reason being that Chrysler was aware of the intended usage of these vehicles.
The "stronger" transmissions consisted of front and rear planet carriers with more pinions, front and rear clutch assemblies with more discs and plates and sometimes larger, higher friction coefficient kickdown bands. Various hydraulic modifications were made by changing spring rates in the valve body and the kickdown band apply strength was altered by a mechanical leverage change. These changes all worked together to give a higher torque-capacity transmission as well as a stronger, more defined shift.
Even these changes weren't enough in some cases. Muscle car units and fleet service units (taxi, ambulance, police, rental, etc.) needed more torque handling capacity as well as severe service capabilities. These requirements brought the home mechanics and aftermarket manufacturers to some of these same conclusions; design and construction of transmission shift modification kits were needed.
Several manufacturers introduced shift improving kits. These kits, when used as directed, were helping to eliminate a lot of premature failure of severe service transmissions. However, most of these modifications for competition and heavy duty service sometimes made the transmission too severe for everyday use. It became apparent that modifications should meet three important requirements: shift performance, longevity, and driver comfort.
Advantages and Disadvantages
The last sentence of the previous paragraph determines both the pros and cons of Torqueflite modifications. In order to get longevity you must give up a small amount of driver comfort. It is basically a trade off. The Torqueflite is designed in such a way to give relatively slow, soft shifts; and the 2-3 shift is the one I think needs the most improvement. To refresh memories, I'll explain the 2-3 shift function again. When the Torqueflite shifts from 1st to 2nd, the kickdown band locks around the Front Clutch Retainer to stop the sun gear driving shell. To make the 2-3 shift, the kickdown band has to hold until the front clutch is applied and then it has to be quickly released. This timing is very important; too early of a band release causes the engine to "rev up" until the front clutch is applied. Too late of a band release and/or too early of a clutch apply is more common; this gives a "putting on the brakes sensation" which is actually called shift overlap (Since the rear clutch is applied in both 1st and 2nd, and nothing has to be released, kickdown band timing is not as critical in the 1-2 shift). Delay in the kickdown band-release and premature clutch-apply both cause overlap and, therefore, friction material wear.
Advantages to Torqueflite modification
Advantage number one to Torqueflite modification is elimination of the 2-3 shift overlap which gives a crisp, efficient shift from second to third, prolonging the friction material life. Why is this not factory accomplished? Probably due to the fact that 90% of vehicle owners believe a soft, slow shift is better on the transmission than a firm one, so original equipment units (excluding factory high performance units) are programmed for this shift.
The second advantage is firmer 1-2 and 2-3 shifts. The word firmer is relative; the shifts are not severe (in most cases this depends on kit manufacturer as well as intended usage), they are just more noticeable. Again, these firm, properly timed shifts eliminate slippage of friction material during shifts. A couple of other advantages are: more fluid is supplied to various hydraulic units which sometimes compensates for seal leakage or wear; and certain kits give control of the 3-2 and 2-1 downshifts to the driver (this comes in handy during hilly terrain). Some valve body modification kits give complete control of the shifts to the driver. These are normally referred to as "full manual" or "full race" valve bodies. Obviously, these are not intended for Imperials or anything used for normal transportation.
Disadvantages to Torqueflite modification
I've only experienced a couple of things I call disadvantages. The most common complaint after modification is due to improper product selection (I use only modification kits from a company called Transgo in El Monte, California. This will be justified and explained a little later). (Neither Allpar nor the WPC Club endorses any product; the recommendations above are the author's opinion only.) The wrong kits will cause too severe 1-2 and 2-3 shifts, harsh park or neutral-to-reverse shifts, and some light throttle 2-3 overlap. Improper adjustments after the modifications are performed also causes light throttle 2-3 "thunk." I use this term to describe the noise you hear when the 2-3 shift is not correctly timed. This is still 2-3 shift overlap (at slow speeds) and minor adjustment usually eliminates this.
Another disadvantage might be the price. Valve body modification kits generally cost from $25 to $65. On the average, when performing the modifications yourself, expect to pay about $55 for a kit, $10 for new fluid and a couple of dollars for a filter. [Note: 1989 prices]
One way to eliminate disadvantages is to select the proper kit. I'll give my recommendations shortly.
Kit Variations and Proper Selection for Required Results
This is the point where I'll plug for what I know works. For the same reason we stick with Chrysler products, I stick with Transgo; performance and dependable results. I've experimented with different types of products and they won't be named here. I've had no severe catastrophes; it's just that the shifts were too firm all the time or they weren't firm enough at the correct time, and sometimes the instructions weren't easy to follow. (Transgo has the exclusive rights to the "Shift Kit" and "Reprogramming Kit" names I'll mention from now on.)
The "Shift kit" or "SK-TF" is a small version of a "Reprogramming Kit." The SK-TF can be used in fleet service and everyday vehicles. It eliminates the 2-3 shift overlap, firms up the 1-2 and 2-3 shifts (not severely), provides more fluid to the front clutch circuit, and gives a bypass to prevent excessively high fluid pressure during cold weather starts and higher RPM service.
Transgo manufactures three "Reprogramming Kits" for Torqueflites. These actually reprogram the valve body; various springs are changed and fluid passages enlarged or restricted to give the correct shifts at the correct time.
A."Tow or Go or TF-1" is for the fleet service and everyday vehicles. Additional driver downshift control and all the features of the "SK-TF" are provided. This is a good kit for motor homes, taxis, and police vehicles; good shifts, firm, yet comfortable
B."Competition or TF-2" is good for full race and extremely heavy campers or motor homes. Shifts are definitely firmer and some driver comfort will be sacrificed. Additional full throttle and down shift control is provided in addition to all the standard Shift Kit features. However, this is still very streetable and reliable (95% of my Torqueflites get these).
C."Stick shift or TF-3" is a full-race, full-manual controlled "Reprogramming Kit." It is very similar to the TF-2 except that the driver controls all up and down shifts (It is convertible back to automatic shifting if required). This is good for full-race vehicles or ones where the driver likes to do a lot of shifting.
Chrysler "Shift-Improver" Kits
For people that stick to Chrysler-engineered products, Direct Connection offers two "shift-improver" kits; one for the 904 and one for the 727. These are inexpensive and easy to install. They work well and they, too, are a good choice for everyday as well as some fleet use. You don't get as much driver control and the 2-3 shift is not as good as the Transgo kits provide but they are still a good value for the dollar.
Everything in the previous section on kit variation deals with external modifications, or things that can be done with the transmission still installed. However, if the transmission is removed, a few more key items can be changed to give bullet proof operation.
Along with a "Shift Kit" or "Reprogramming Kit," revised clutch clearances and band adjustments can be made. I also add a higher friction coefficient kickdown band to every high-performance unit I build. This makes an incredible 1-2 shift and it only costs an additional $30-$35 (The 1-2 shifts are firm enough that I don't recommend this for luxury vehicles). I use Raybestos-Manhatten waffle-cut front clutch discs and Raybestos-Manhatten smooth rear clutch discs and Perfect Circle steel sealing rings. Good overhaul gasket and seal kits are available from many different sources so check around. To finish it off, normally I install the "Direct Connection deep pan and pick-up" package from Chrysler.
By following simple recommendations available from Transgo, a home mechanic can really assemble a neat package. Using these suggestions and products has allowed me to build many street and race Torqueflites with zero failures. I attribute 75% of this to product selection and 25% to very careful attention to assembly details.
To write an article on modifications is rather difficult without mentioning manufacturers' names. I don't intend to down-grade ones I don't use or aren't familiar with; that's why I mentioned only the few vendors I did. I know what has worked best for me and I'm sure the same results are possible for anybody.
Should you modify your Torqueflite? If you want it strictly original, no. But if you want added reliability and performance and you have some mechanical skill or a friend that does, set aside a couple of hours and start on your transmission. If it's already out of the car, read Transgo's additional recommendations, and decide what you really want your transmission to do for you.
The Torqueflite is relatively straight forward. You'll get a lot of enjoyment with a minimum of problems out of your modified Torqueflite if you are careful. Remember to keep your Chrysler service manual handy and follow whatever kit instructions you finally decide upon. Write in a letter, through the club office, if you have any questions on where to get kits and literature, etc.
Part three: problems and repairs (by Tom Hand)
This is the final section of a three part series devoted to the Chrysler Torqueflite transmission. As in the two previous sections, I'll deal with the 904 and the 727 together. I'll touch on the lock-up units but not go into any great detail on them. The front wheel drive transaxles will not be discussed. I've broken the "Problem Recognition" section into separate groups; one on "Long Term" problems such as leaks or gradually increasing noises and the other on "Immediate" problems caused by accident or misuse. In the "Test Sequence" section, I've discussed the different methods and an order in which to perform them for proper Torqueflite repair. The final part will be on "Repairs in and out of the vehicle." A "what's on when" chart will also be given to aid in clearing up any questions as to what actually operates in each gear.
When your transmission's performance is erratic, you've got three basic options. Number one is ignore the problem and hope it goes away, number two is: take the vehicle to a repair shop being completely in the dark as to what could be wrong and hope for the best, or number three is learn about the transmission operation to either allow you to logically diagnose your own problem or at least to understand what a professional technician is telling you. Usually, most ignored problems get worse instead of better so solution number one is eliminated. Answer two could cost you dearly in both time and money in case you don't have an honest person to aid you in your time of need; therefore, this isn't the smartest answer either. Number three makes the most sense and is normally not as hard as it seems.
Chrysler prints some of the best troubleshooting information available to the public in every Factory Shop Manual. Everybody that intends to do any Torqueflite work should have some sort of a shop manual to refer to. Not only do they tell how to find the problem, they tell logically how to verify it and repair it. Since not everyone has the tools or area to work on their own transmission, a service manual can at least give you something to refer to when somebody else diagnoses your problem.
I recently acquired the new "Fundamentals of Automatic Transmissions and Transaxles" from Chrysler and it is easy to comprehend and very thorough. It is available from the Chrysler Training Center. The number on it is TM-508A and the cost is about $10-$12. You won't find a better manual covering 904s, 727s or the new transaxles for this kind of money anywhere.
The Chrysler manuals or other training and repair manuals will be a valuable help to any method you choose to get your Torqueflite repaired.
I've separated this problem section into two groups, one being "Long Term" problems and the other "Immediate" problems. Similarities exist between both groups, so I have some overlap in the discussions (I will list everything that can occur; the Chrysler service manuals have very complete charts for this. I'll give problems I see most often).
Long Term Problems
I've titled this "Long Term" because of the extended time it takes for some of the problems to appear.
One of the most common problems to appear is an oil leak. These can be either static or dynamic; static being those leaks that seemingly occur while the vehicle is stationary and dynamic being leaks during vehicle motion. Leaks that occur statically also occur during motion but sometimes they aren't as obvious. Pan leaks, shifter shaft seal leaks, filler tube 0-ring leaks and front pump gasket and 0-ring leakage can all be considered as static leaks, remembering that they also leak worse during vehicle motion.
A bad front oil seal, speedometer gear seal, cooler lines, extension housing seal or torque converter will generally leak most during vehicle operation. The oil pump has to be functioning to get fluid under pressure to the front seal and to the cooler lines, and the torque converter must be spinning to throw oil from any cracks that may be around the weld (this is normally only found on remanufactured converters).
The speedometer gear and extension housing seal generally only leak when the output shaft is turning which is normally while the vehicle is in motion. Most of the leaks can be fixed while the transmission is in the car or truck with the exception of the pump related leaks (i.e. front seal, pump gasket or pump 0-ring).
The leaks I see most often are the pan gasket, shifter shaft seal, and the front seal. If nothing has been touched on an original transmission, leaks start because of normal wear and/or heat effects. Changing the filter and fluid and not correctly tightening the pan bolts will sometimes cause a pan leak. Using some of the harder gaskets such as the one contained in the D.C. Deep Pan package will also cause leaks (I stick to cork in all cases). A special tool is sometimes required during the shifter shaft seal replacement operation but it can be done while the transmission is installed. As mentioned previously, the pump leaks can only be repaired with the transmission out. Once it is out, it would be a good time to pull the pump and inspect the friction material in the front and rear clutch drums. Special slide hammers are needed for this operation but they are relatively inexpensive. Check the bushing that the converter hub rides on for excessive wear and replace the steel sealing rings on the reaction shaft support and the input shaft. The extension housing seal, speedometer gear seal, dipstick 0-ring and pan gasket are all relatively simple and inexpensive to repair even with the transmission still installed.
Another long term problem has to do with noises. Some noise is normal during first, second, and reverse gear because of the planetary gear motion. However, as miles accumulate during normal or competition use, first gear tends to get more noticeable. Since both first and second gear use some of the same planetaries, the noise will sometimes be present in second gear but generally not as loud. All you can do about this is replace the worn planetary gears after removing the transmission from the car or truck. No additive is going to quiet worn planetaries forever.
A high-mileage torque converter sometimes has a whirring or buzzing noise to it. (Mine exhibits this problem currently.) If it is severe, the converter will need to be changed.
The high pressure relief spring and ball in the valve body will sometimes buzz in reverse but this is normally nothing to be concerned with. (A Transgo Shift or Reprogramming Kit will correct this.)
Clunks and bangs during gear engagements usually are driveshaft noises and not transmission related. A worn output shaft support bearing will be a "groan" in all gears except park and neutral but I haven't seen one wear out yet. Noises almost always require transmission removal to repair them properly. Again, if the planetaries are loud, you've got a lot of use and/or miles accumulated so you might as well go through the whole gear box.
The last long term problems are usually the hardest to diagnose. Shift related problems sometimes take a long time to surface as you can have long, drawn-out shifts, incorrectly timed shifts, slipping shifts or non-occurring shifts. All of these can start out almost non-noticeable and then get continually worse.
A common but easy discrepancy to find might be a slipping second gear which eventually changes to no second gear. Many things could be wrong but if the fluid is the right level and everything else is correct, the kickdown band is probably out of adjustment, worn out, or broken.
On pre-1971 727s and especially hard used units, it wasn't unusual to get engine spin or flare-up during the 2-3 shift. This is more often than not turned into the loss of 3rd gear with reverse quick to follow. Chances are the steel rings sealing the front clutch retaining drum to the reaction shaft have worn themselves or the I.D. of the drum. This was probably caused because the narrow bushing in the drum allowed the drum to "wobble" on the reaction shaft causing the rings and/or drum to be worn prematurely. From 1971 on, the bushing was lengthened and a few other front clutch items were redesigned to eliminate premature ring and drum wear.
Some of the older units had symptoms of low fluid during operation when in actuality, the level was correct. This was probably due to a partially clogged filter. In 1973 the filter was enlarged approximately 50% to prevent early restriction (if nothing is wearing out, the filter will probably never plug anyway).
I've really never seen too many pre-1978 Torqueflites "wear out" or break that haven't been either misused or neglected. Probably the only major trouble I can think of relates to the 1978 and later model year lock-up converter 904's and 727's. The torque converter had a piston and friction disc inside it that locked the turbine solid to the impeller front cover. This in effect eliminated any slippage in the converter and helped fuel efficiency. (The lock-up only happens after the 2-3 shift.) A few of the early complaints with the lock-up units were sluggish vehicle performance, pinging, bad cold weather performance, dying in reverse and most of all, vibration and surging after lock up. Diagnosis showed some units were locking too early and dragging the engine down (restricted cooler lines or worn oil pump drive gears sometimes caused the converter clutch to lock in reverse which killed the engine). The fix for premature lock-up was to install a different spring in the valve body to raise the lock-up speed. The pump clearances were also tightened to make sure ample fluid was available to keep the converter operating properly and prevent lock-up in the wrong gears. The lock-up Torqueflites probably caused more headaches for service technicians than any other previous units.
Immediate problems are almost always caused by abuse or neglect on the driver's part. Some service literature will not accurately describe what really might have happened so I'll list some of the failures I've seen most.
The problem I see most often is early, soft or slipping gears combined with no full-throttle downshift. Remembering back to the section on valve bodies, you'll recall that the throttle pressure rod coming from the carburetor tells the transmission how firm and how late to shift depending upon throttle position. Most often, the original carburetor has been changed on the vehicle in question and the linkage has been disconnected or just left off. This is one sure way to guarantee friction material wear and eventually transmission failure. The throttle rod has to be hooked up and adjusted correctly unless a special racing valve body has been installed.
A very expensive problem caused by abuse is case failure at the over-running clutch attaching point. Both the 904 and 727 case can be totally destroyed by "neutral drops or reverse drops" or, in other words, full throttle in neutral or reverse and then immediately shifting to drive. A few of these "slams or drops" will generally wipe out a good case no matter how the transmission is assembled.
Winter causes many different difficulties for the Torqueflite. In some cases, immediate problems can occur from placing the selector in reverse with the engine racing in the fast idle position. This will sometimes break the low-reverse band or blow out the front clutch piston seals due to the excessive fluid pressure (The high pressure relief circuit in the valve body should prevent this). A solution is to get the fast idle set correctly.
Getting stuck in the snow might cause you to have to rock the car by shifting from reverse to drive rapidly. Think about this and compare the price of a tow truck to a transmission repair because too much rocking might break the low-reverse band, over-running clutch, or the case, so it may be cheaper to get the tow.
I notice some sluggish performance during sub-zero temperatures with my 904. I normally warm the converter and fluid by putting the transmission in drive and holding the brake on to keep the car stationary. This circulates fluid through the converter and warms it quicker (The best and preferred way is to just drive the vehicle carefully during cold weather the first mile or so)
Other things can be destroyed by drag racing or severe service and it would be hard to list them all here. Just remember to start with good equipment before you abuse it or use it beyond its intended limits. Heavy duty transmissions can handle a lot of horsepower but when they go, get your wallet out because it probably won't be cheap to repair them.
I'm going to give a sequence that a person could follow once he has noticed a problem and wishes to diagnose it (all this is listed in the service manual but I'll give a basic order that can be followed).
You drive the car everyday that is having trouble, you are probably already past this stage. Make note of shift points for proper timing and firmness. A soft early shift or late firm shift should tell you again to check the throttle rod assembly. If the gears are not where they should be on the indicator, or if the starter doesn't spin in neutral or park, check the shift linkage as your problem is probably here.
Next, pull the dipstick while the transmission is warmed up, the engine idling and the selector in neutral. The fluid will be between "add" and "full" if it is correct. Sometimes, even a half of a quart too high to too low will cause problems (Remember the converter does not fill during park so the dipstick will show "overfill" if you check it in park. (Always use neutral). Look to see if the fluid is relatively clean looking and not burnt smelling. Appearance is sometimes deceiving because the new Dexron II fluid looks brown when it is new. Check the oil for a gritty feel. If you've had a lot of slippage or completely lost a gear, the oil will probably smell. You will be getting to pull your transmission soon.
Watch for antifreeze in your oil. If you find it, it's probably already too late because the clutch and band lining are probably gone. Antifreeze in the fluid is pretty hard on friction material. Make sure the transmission cooler in the radiator tank is not leaking. External coolers installed on Hemi's or police cars won't allow antifreeze or water to get in the transmission because there is no direct contact between the transmission cooler and the radiator.
If you do decide to change the fluid, drain the converter also and blow out the cooler lines with them disconnected at the transmission and change the filter. Normally the original fluid is not to be changed except for high performance or severe service situations.
*Using Type F instead of Dexron II fluid will sometimes give firmer shifts so make sure you are adding what you want.
The next thing you should check is the linkage; both the throttle and shift linkage. Improper throttle linkage will give early, soft shifts or late, firm shifts. Check this for correct adjustment often. The shift linkage can be easily checked by insuring that the engine starts only in neutral and park. Generally this will set the other gear positions correctly.
A not so obvious thing to watch for is the state of engine tune. A poorly running engine will usually cause late, firm shifts because the throttle is being held down much further than normal. Be sure the engine is running normal before blaming the transmission for erratic shifts.
If you've studied the "What's On When" chart and the problem is still not clear, get a 300 psi oil pressure gauge and find the attaching points happening during transmission operation. The service manual goes into detail on this (I've never had to do this because usually the problem is so obvious the "What's On When" chart tells me where to look first. A little experience allows most people to be able to do this).
You can also drop the valve body and apply air pressure into the various case passageways to find a blown clutch seal if you should determine this to be a possible problem causing improper operation. Again, refer to the service manual for details.
Repair In and Out of the Vehicle
As previously stated, some things can be repaired with the transmission still installed. A slipping second gear can sometimes be corrected with a kickdown band adjustment. Almost all fluid leaks with the exception of pump related seals, can be repaired without removing the transmission. A sticky governor can be repaired as well as sticking valves in the valve body (I've never run across either of these yet). In fact, most minor problems can be corrected without removing the transmission. A lot of times, a Transgo "Shift Kit" or "Reprogramming Kit" will correct minor shifting problems and prolong the Torqueflites usable life.
Loss of any gears, noises or leaks in the oil pump will require removal of the transmission. Again, this is a good time to go through the whole overhaul procedure if you feel certain you can do it or you have a trustworthy mechanic. The real key to troubleshooting is to follow a prescribed sequence until you are able to locate the problem and correct it.
I've had a good time writing this article on Torqueflites. Part One gave a general understanding as to how the Torqueflite really operates. Part Two was shorter but hopefully still informative on the subject of Torqueflite modification. I've tried to make this final part as helpful as possible when it comes to troubleshooting common problems with the Torqueflites.
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