The 4T65-E: ‘Slip-Sliding Away’ - Transmission Digest

The 4T65-E: ‘Slip-Sliding Away’

Three to six months after you overhaul a 4T65-E transaxle, the vehicle may come back with a code, either P0730 (incorrect/undefined gear ratio) or P1811 (maximum adapt and long shift). Generally, code P0730 occurs immediately after installation of a transaxle with an incorrect ratio. This could mean that either an exchange unit with an incorrect ratio was installed or incorrect sprockets and/or final drive was used during rebuild in the shop.

The 4T65-E: ‘Slip-Sliding Away’

Technically Speaking

Author: Wayne Colonna, Technical Editor

Technically Speaking

  • Author: Wayne Colonna, Technical Editor

Three to six months after you overhaul a 4T65-E transaxle, the vehicle may come back with a code, either P0730 (incorrect/undefined gear ratio) or P1811 (maximum adapt and long shift).

Generally, code P0730 occurs immediately after installation of a transaxle with an incorrect ratio. This could mean that either an exchange unit with an incorrect ratio was installed or incorrect sprockets and/or final drive was used during rebuild in the shop.

Code 1811 is a very common code, and in most instances replacing the pressure-control solenoid with a slight tweak (clockwise 1⁄8 turn) to its adjusting screw cures this ailment. But when the vehicle returns weeks or months later with one of these codes, you may begin to second-guess that new pressure-control solenoid.

Perhaps you erase the code, give the vehicle a road test and find that it shifts well and the code didn’t come back. You think, “Well, maybe the trans just had a slight hiccup – you know, a stuck valve. Ah, yes, that wishful thinking, sort of like crossing your fingers, you know. So you give the vehicle back to the owner with that uneasy feeling in the deepest part of your belly that it will return, and it does – maybe the next day or a week later, but it does come back. Now what? Change the pressure-control solenoid?

How many times while rebuilding a 4T60-E or 4T65-E have you said to yourself that the clearances in the 2nd- and 3rd-clutch packs always seem to be excessive (see figures 1 and 2)? You may have even tried to find clearance specifications and learned that GM does not publish them. The company’s reasoning is that if you are putting in the proper OE-sized parts, you will automatically be within acceptable tolerances. Yet even with the right parts, the clearance still seems to be excessive.

Of course, if you are re-using good, experienced frictions, the clearance may be even more excessive. But many times the unit is built with those loose clutch packs and it road-tests well, so it seems to become a moot point. And it also becomes an overlooked area weeks or months later when the vehicle is finally back having a problem with the 4T65-E transaxle. You see, unlike the 4T65-E, the 4T60-E does not have a computer strategy that will snitch on the transmission if it slips. The 4T65-E has a turbine-speed sensor, allowing the computer to monitor gear ratio against the vehicle-speed sensor, so what may have been happening all along with 4T60-E transaxles is now being discovered in the 4T65-E.

The clearance of the clutch pack combined with the driving style of the owner will determine whether this problem ever presents itself. So if the second clutches are too loose and the driver gets heavily into the throttle, the clutch could slip and produce the P0730 code. If the clutch-pack clearance is not too excessive and the driver has a light foot, it may never be a problem. This, in part, is what makes the problem so elusive.

Other reasons for this problem being so spotty include that the computer will first try to compensate for the slip by increasing line pressure before setting the code. If this works, a code is not set, but if the higher line pressure can’t hold it together, a code is set. This computer strategy actually could be helpful in diagnosing the problem. Let me explain how by first clarifying what it takes for the PCM to set codes P0730 and P1811.

The computer has a strategy called an adaptive modifier that controls the execution of the shift. If a shift takes longer than 0.65 second and the adaptive modifier cannot shorten this time by increasing line pressure, a counter inside the computer increases by one. If this happens twice in one drive cycle, the computer will set code P1811.

If the shift takes place in less than 0.65 second, the PCM then begins to watch the current gear ratio. Whether the transaxle is in first, second, third or fourth gear, if the PCM notices excessive slippage in that gear lasting more than six seconds, it will set code P0730. The computer will try to compensate for this slip by first raising line pressure.

Here is where the computer strategy may be helpful in the diagnostics: Sometimes by viewing parameters for shift error, shift time and transmission adaptive pressure (TAP) cell, you can get clues as to where the problem may be. The parameters for 1-2, 2-3 and 3-4 shift error will display the difference between the desired and actual shifts in seconds. A negative number equals a longer shift time, and a positive number equals a shorter shift time. The 1-2, 2-3 and 3-4 shift-time parameters display the previous shift time in seconds. The 1-2, 2-3 and 3-4 TAP cells display adaptive pressure needed to make a shift in the proper time. A large number indicates that an increase in pressure was required to correct a long shift. The steady-state TAPs display in kilopascals (kPa) the pressures it took to keep the unit in that gear. A large number indicates that the PCM had to increase pressure to correct slippage in that gear.

Now let’s think back to the 4T60s (the 440-T4). Some of you may recall that burned second clutches would produce 2-3 flare rather than a slip on the 1-2. Similarly, second-clutch slippage under heavy throttle in a 4T65-E transaxle could be revealed throughout second, third and fourth gears, whereas third-clutch slippage would be observed only in third. Look at the parameters for shift error, shift time and TAP cell and see whether you could spot line-pressure compensation that would point you to the problem area.

A rule of thumb that most seasoned vets know and has proved itself worthy through the years is that you should have 0.008-0.012 inch of clearance per friction plate. This allows you to do some modifications of your own. Here are some things you can do with the 2nd and 3rd clutches to tighten them up.

The second-clutch drum contains six frictions, which means we can have a total clutch clearance of 0.048-0.072 inch. For the second clutch, Alto produces steel plates that are 0.090 inch thick, about 0.020 inch thicker than OE (see Figure 3). By using one, two or three of these steel plates, you easily can bring this clutch drum down to a tighter tolerance (see Figure 4). Alto’s part number for this steel plate is 062733-228.

For the third clutch, you could use the thicker earlier (’85-88) single-sided friction plates to take up the play, or you could take an existing external-tooth plate and remove the friction material with a wire wheel (see Figure 5). This will leave you with a 0.050-inch steel plate that gets placed on top of the wavy plate, followed by another single-sided external-tooth friction plate (see Figure 6). Stack it up as usual from here, and many times you bring the pack down to about 0.060 inch total clearance (see Figure 7) – pretty good for a five-friction pack.

Even with these adjustments, you still may encounter code P1811 after a 2-3 upshift during acceleration of two-thirds to full throttle. If this should happen, you usually can resolve it by enlarging the 3rd-clutch feed hole in the spacer plate by 0.010 inch (see Figure 8).

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