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by Tom Hand, 1983Courtesy of the Walter P. Chrysler Club. Also see our TorqueFlite main page.
Part 1: History/how it works • Part 3: Troubleshooting and Repairs
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; why the majority of 904s and 727s can benefit from a few well proven alterations; and advantages and disadvantages to modifications. There are many types of kits made to improve Torqueflite and I'll give my recommendations on the ones I'm familiar with.
Some may question 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, I got a spare valve body from a salvage transmission and followed the Chrysler service manual in disassembly and reassembly. After I determined that the valve body was operational and 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.
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; Chrysler was aware of the intended usage of these vehicles.
The “stronger” transmissions had front and rear planet carriers with more pinions, front and rear clutch assemblies with more discs and plates and sometimes larger, and higher friction coefficient kickdown bands. 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 and 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 sold shift improving kits. These kits, when used as directed, eliminated a lot of premature failure of severe service transmissions. However, most of these modifications for competition and heavy duty service made the transmission too severe for everyday use. It became apparent that modifications should meet three important requirements: shift performance, longevity, and driver comfort.
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. The Torqueflite is designed to give relatively slow, soft shifts; the 2-3 shift is the one I think needs the most improvement.
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 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 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.
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.
These firm, properly timed shifts eliminate slippage of friction material during shifts. More fluid is supplied to 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.
The most common complaint after modification is due to improper product selection. 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.
One way to eliminate disadvantages is to select the proper kit. I'll give my recommendations shortly.
Neither Allpar nor the WPC Club endorses any product; the recommendations above are the author's opinion only.
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. 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.
For people that stick to Chrysler-engineered products, Direct Connection had 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 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 straightforward. 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.
TorqueFlite overview / main page • Main transmissions page • Identifying and exchanging Torqueflites
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