Note: Allpar does not take responsibility for the veracity of any information or opinions here, does not claim expertise, and is not responsible for any consequences. Please proceed at your own risk.
by Tom Hand
Courtesy of the Walter P. Chrysler Club with our most sincere thanks. First published in 1983. See our TorqueFlite overview / main page.
See Part 1: History/how it works, and Part 2: Modifications
This is the final section of a three part series devoted to the aluminum-cased 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 [as they were fairly new when the article was written].
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. Troubleshooting methods are described in the "Test Sequence" section. 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, ignored problems get worse, so solution number one is eliminated. Answer two could cost you dearly in both time and money if you don't have an honest person to aid you in your time of need. 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 thorough and easy to comprehend. It is available from the Chrysler Training Center, number TM-508A. 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 titled this “Long Term” because of the extended time it takes for some of the problems to appear.
The reverse lever shaft O-ring leak fools most everyone into thinking the oil pan is leaking when it is not. This only happens with the 727 transmission, because on the 904, the extension housing does the sealing.The “butt” end of the lever shaft can be seen above the oil pan from the rear. There is a cast-in “tang” on the extension housing which prevents the shaft from moving out of the transmission case; that’s its only means of retention.With the shaft removed, one can see an O-ring at the rear end of the shaft, only about a 1/4” in from the end. On later transmissions there are two ring grooves, though only one O-ring is installed. A smart person would install two O-rings for added leak prevention.The correct repair is to remove the extension housing and the trans oil pan. On some pins, there is a drilled and tapped hole in the end into which a screw can be installed in order to give you something to pull the shaft out with. On others you need to push the shaft out from the inside of the transmission case after removing the valve body. It is amazing how that one is always overlooked except by Chrysler techs familiar with years of experience rebuilding these transmissions, even then, some flat-raters miss this important O-ring as well.The O-ring hardens over the years and allows oil to seep out of the transmission when the vehicle is parked for extended periods and the torque converter slowly drains half of its fluid into the transmission case. This overfills the oil pan’s capacity and the fluid reaches to the level of the reverse lever shaft and passes out through the hardened O-ring.— Hemi Andersen
This was a long explanation, but one that MUST be mentioned as it is one of the most problematic oil leaks on the 727 other than the ‘Shift Shaft Seal’ which is mentioned in the article.
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.
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.
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 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, probably because the narrow bushing in the drum allowed the drum to "wobble" on the reaction shaft. 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 the level was correct, 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 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 904s and 727s. The torque converter had a piston and friction disc inside it that locked the turbine solid to the impeller front cover. This eliminated slippage in the converter and helped fuel efficiency.
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 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. The throttle pressure rod 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, and the linkage has been disconnected or 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.
An 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” — going to 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.
Hemi Andersen wrote: “Another way for the driver to avoid this is to shift into Drive 1 first, then very quickly shift into Reverse. A permanent solution is to set the idle speed correctly.”
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.
Editor’s note: since this was written, synthetic transmission fluid has become an excellent way to avoid cold weather damage. Chrysler’s own ATF+4 has a synthetic-oil base and should be better in winter and summer alike.
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.
If you drive the car every day, 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 (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 in Hemis 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.
The next thing you should check is 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.
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 (except 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 kit will correct minor shifting problems and prolong the Torqueflite’s 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.
TorqueFlite overview / main page • Main transmissions page • Identifying and exchanging Torqueflites
More Mopar Car and Truck News
Death of the Pentastar V6 • 2017 Heavy Duty Turbo Diesel Dyno Battle:... • Dodge Demon hints...