Читать книгу Chrysler TorqueFlite A-904 and A-727 Transmissions - Tom Hand - Страница 11

CHAPTER 3

TROUBLESHOOTING

Troubleshooting is simply finding and fixing a problem. With the TorqueFlite, identifying the problem and knowing where to look for its solution is sometimes tough. This chapter helps focus attention on the internal assemblies and exterior parts that often create common issues.

Like any device designed and assembled by humans, TorqueFlites are not infallible. Over time and with use, their elastomeric materials change due to fluid exposure and heat. Friction materials wear out. Springs change tension. Wear particles from gears and friction materials end up in the wrong places. Driver abuse and neglect take a toll. Eventually, several things combine to cause operational and shifting issues, noises, leaks, and worst case, catastrophic failures.

In 1970, Superbirds stood out because of their long nose and big wing. This brilliant white one retains its original A-727, which was rebuilt in the early 1980s.

Troubleshooting is a bit more difficult now compared to when the TorqueFlites were new because, over time, owners have made “improvements,” swapped parts, enlarged transfer plate holes, and changed springs in the valve body. Many degrade due to storage. Fixing them when they were newer was relatively straightforward; you made sure their parts met the original specifications and you adjusted everything according to factory specifications and engineering changes. Unfortunately, as time passes, original parts are replaced, and original engines and carburetors and the matching throttle pressure linkage, manifolds, and levers are long separated.

Combine several changes and it becomes apparent why it is much more difficult to predict and explain what could be wrong and why it may be tough to find and fix every problem. Unfortunately, (or fortunately, if you have fun doing it) TorqueFlites may simply need to be removed for repair. It is not uncommon to buy a vehicle that has what seems like a simple transmission issue, but that turns into something much more difficult. Often, you just have to return it to its original condition. Knowing the history of the transmission is very important, but many times, it may just not be possible.

In this chapter, information from factory and aftermarket literature is combined with input from experienced mechanics to highlight TorqueFlite operational issues, what could cause them, and what steps can be taken to correct them. Fortunately, because A-904s and A-727s are closely related, troubleshooting is similar.

There are three “Trouble” charts provided in Appendix B: one that deals with troubles that can be diagnosed and fixed with the transmission in the vehicle, a second that requires removal of the transmission/converter for repair, and a third that is exclusively for lock-up converter-equipped problems. Noises and fluid leaks are discussed.

There is a logical and ordered sequence that should be followed when troubleshooting a transmission. By doing it in this way, simple things can be identified and corrected first. One manufacturer states it most eloquently: “The logical and proper procedure is diagnosis before disassembly.” In other words, identify the problems and use your knowledge of how the TorqueFlite works before automatically jumping in and tearing it down.

Fortunately, there are a few basic things that cause most of the trouble.

• The fluid level is too high or too low.

• The throttle pressure is wrong.

• The engine is not running right.

• The shift linkage is not correct.

• The band(s) is out of adjustment.

And if correcting these easy things doesn’t fix the problem, there are always more complex things to look at.

• Hydraulic pressures are out of specification.

• Internal hydraulic issues are present.

• Mechanical failures have occurred.

• Mismatched parts and technology are combined.

Chapter 2 offered insight as to how the TorqueFlite actually works so one can understand what the transmission is doing in each gear. Diagnosing in the proper sequence helps the problem be identified quicker.

• The basic things should always be checked and corrected early.

• To gather additional operational data, a diagnostic road test can be taken (if drivable).

• After road testing is complete, you may be able to decide what is wrong. If not, hydraulic pressure tests can be made to provide more internal information.

• If after pressure testing, the problem is still not apparent, removal of the valve body lets an air-pressure test be made of the transmission to determine the condition of the hydraulic sections.

• Torque converter issues may be part of or even the whole problem; the “nerve-racking” converter stall test can be performed.

Rough Steels

One of the things done to increase torque capacity is to increase the quantity of friction discs and steel plates in the front clutch retainer. This requires a larger, deeper retainer, thinner steels, thinner frictions, or a modified piston (along with extra return springs) or any combination thereof. For an A-727 behind a worked-over 340, I thinned some front steel plates by getting them ground and then smoothed them out with a light sand blast, followed by a lot of sanding. I then added thinner rear clutch friction discs and was able to install seven (I believe). It worked pretty well with a nice firm shift at wide-open throttle. After a few days, I needed to make a minor kickdown band adjustment to eliminate the spin-up that started during light throttle 2–3 shifts. I knew everything was right so it must have been just the kickdown band wearing in. A few more days and another band adjustment was needed. A few more days and another minor readjustment did not take care of it.

I knew the pressure was right and the fluid level was correct. The fluid looked a little darker, but that was expected. The throttle pressure was reset, but it was close enough. No way could it be my modifications. I suspected the kickdown band was failing so out the transmission came. The pump and the front clutch retainer, along with the kickdown band and kickdown servo, were removed. The band and servo were perfect. The front friction discs, unfortunately, were devoid of almost all friction material. Those custom steel plates that I just knew would smooth out and be polished by the “sort of rough” friction discs looked the same as when they were installed.

Would any additional tests have identified this issue? In this case, the history of the transmission needed to be understood. Testing the transmission may have provided some answers, but questioning the transmission mechanic’s background in physics would have told the story. (Always remember, steel plates have to be smooth and almost polished to avoid damage to the less durable paper-based material they interleave with. Rough metal almost always wins against paper.)

By combining (1) the information gathered from the tests, (2) data in the three troubleshooting charts, and (3) any known history of the TorqueFlite in question, you should be able to determine the problem and identify the fix needed.

Fortunately, some of the simplest things to check cause the highest percentage of problems. Pulling the dipstick to check the fluid level, verifying that the shift linkage is close, and checking the throttle pressure linkage can all be performed rapidly and without any tools.

Fluid Level

Start by checking the fluid level. With the engine at a general idle speed and the fluid warm to hot, the fluid level in Neutral should be between the “full” and “add one pint” level. If it is too low, the pump, via the filter, can suck in air causing all types of hydraulic issues. It the level is too high, the gears and spinning parts can whip the fluid into a foam or froth, which also causes similar issues.

While checking the level, look at the fluid to be sure it is red or light brown; it should never be black, burnt smelling, or have flakes or tiny metal particulates in it. Newer fluids tend to smell more burnt so you may have to put a few drops on a white cloth to see if it is blackish or dark brown. If there is metal in the fluid or pieces of things floating around in it, it is likely too late.

This filter did its job; the size of metal particles and friction material flakes it caught range from microscopic to 1/16 inch in diameter.

Your first step should be to check the fluid level. This one is down a pint, probably due to a pan gasket leak.

Adding type 7176 Mopar fluid brings the level to the lower part of the range.

Shift Linkage

With the fluid level verified, check the shift linkage, whatever kind yours has. Assuming the neutral starting switch is functional, move the shifter to “Park” or “P,” and if the starter spins over when you turn the key, it is good (so far). Move the selector to “N” and hit the key again. If it spins over in “N,” the linkage is probably pretty close. If it just misses each position by a little bit, look at the linkage to see if the pins are worn out, or the holes are elongated, or the plastic bushings are shot.

If you have an aftermarket shifter, you may have to slowly “feel it” through all the detent positions to be sure it is even close. At one extreme it has to be in “L” or “1” and at the other it has to be in “P.” Often, the levers that may have been put on your transmission may be the wrong length and you may have “P” or “L” (“1”) but not both.

As difficult as it is to drill holes or modify expensive aftermarket parts, levers may need drilling so “P” and “L” are correctly located and that in “N” and “P,” the starter spins over. Many times it is as simple as changing to the correct lever on the transmission manual valve shaft but it may be hard finding the right one. The total distance the shifter lever moves at the cable attaching point has to match the distance the cable attaching point of the manual lever moves.

Throttle Pressure Linkage

This is by far the most important signal the stock TorqueFlite needs to work properly. The throttle pressure signal tells the valve body where the carburetor or throttle body lever is at any given point in time. Is the engine idling or under load? Is the throttle wide open or did the driver just lift off the gas? The linkage transmits the signal that tells the transmission how hard to shift, when to shift, when to downshift, and when to ease up or increase pressures. If the throttle pressure linkage is wrong, most everything about the shift is wrong. It must be correct.

An intake and carburetor change usually requires a change in the length of the throttle pressure link. As a temporary fix, a 1/4-20 bolt and nut was added to make up the gap.

This longer throttle pressure link corrects the differences caused by a swap.

With the new link on, the rear of the slot is at the throttle linkage pin allowing pressure to be set correctly.

Unfortunately, even though the “top side” of the engine’s linkage can be correct, the lever on the transmission may be wrong. The 2- and 4-barrel engines often had different linkage lengths and shapes, so it may be as easy as switching to a shorter lever or one with the different angle if your linkage is still off. As long as the throttle pressure linkage follows the carburetor or throttle body pin and ends up close to full detent when the carburetor or throttle body is wide open and it goes back when at idle, you can get by without damage. Leaving it off because you do not need “kickdown” is never, ever acceptable unless the lever on the transmission is tied to keep pressure on the internal throttle valve. Even then it is truly only correct at one position unless it is a manual valve body and the pressure is maxed out.

The shift linkage on this 1987 truck uses two plastic bushings to support the horizontal shaft. Always check these for looseness if you experience starting or manual shifting issues.

This bushing is on the transmission side bracket. The lever on the shaft uses another molded bushing into which the linkage snaps. Older TorqueFlites have pins in holes held with clips and cotter pins. The bushings or holes and pins can wear making linkage feel sloppy and cause starting issues.

This truck has a 500-cfm Edelbrock AVS carburetor and an owner-modified throttle pressure link. With the nut and bolt, the rear of the link touched the pin, although it was not the right way to solve the mismatch.

There is another way to take care of mismatched throttle pressure linkage. Bouchillon Performance Engineering and Lokar Performance Products sell cable-operated throttle pressure kits that replace the OEM mechanical rods and linkage. The parts they come with help you adapt to most any combination, and their instructions detail how to set the pressure correctly at idle and wide-open-throttle conditions. If you have changes that render the rod-type linkage too difficult to use, either of these should help.

This bushing is under the driver’s left foot; often overlooked, it is critical to proper gear selection.

At wide-open throttle, the link pushes the throttle valve in the valve body correctly.

“Adapting” to Change

If you have a non-stock carburetor or throttle body, adapters from Edelbrock and Holley help get the linkage adjustments back within stock specifications. The key thing is the throttle valve inside the valve body needs to move in unison with the throttle pin on the carburetor or throttle body. For this to happen, the linkage from the manual shaft on the valve body to the throttle body or carburetor needs to be right and have similar geometry. In other words, the total movement of the carburetor or throttle body pin needs to match the total movement of the lever at the transmission.

Here’s an example. On a 1968 Barracuda with an A-904, the throttle pressure rod’s connection on the transmission to the upper bell crank is adjusted according to factory specs, and it moves roughly 1⅝ inches from baseline (closed) throttle pressure to maximum (wide-open) throttle pressure. Therefore, for the transmission to receive the correct signal, the item that actuates or pushes the bell crank also has to move a total distance of 1⅝ inches. Fortunately, a 4611 Carter AVS (a 1969 340-ci V-8 original carburetor) pin that the throttle cable and throttle pressure link attaches to moves 1⅝ inches from dead closed to wide-open throttle. However, if you toss on a typical Holley carburetor “out of the box” and have to move the pivot pin to the only hole on the Holley that it fits in, which is farther away from the throttle blade’s shaft, the total movement from closed to wide-open throttle is 2¼ inches. If you hook the throttle pressure linkage to it, you find it is out of alignment side-to-side and the length is way off. If you are crafty, you make it fit, but it still may not work. The carburetor can be at idle with the throttle pressure link adjusted so the back of its groove hits the pin on the carburetor lever.