ttuling

I think that's different from what other folks here logged a couple years ago, but might be misremembering. It would certainly put it in a different light than the dominant paradigm which is that the TCM drives every hunting cycle, for some unknown reason (varying signals from ECM, sticky or sloppy responses to N218 changes, something else).

Logs of non-hunting transmissions show that it spends a lot more time in partial lock than one would expect by how it feels, so there's probably nothing wrong about that aspect of what you observed.

Tom

PaulW

I have two, one from a 97, one from a 98, and they both act the same way. The throttle position indicator is not "adapted" as the facelift cars are after installation. That's one reason why I think it is a possibility.

CalG

The transmission temp sensor inhibits the TCC lockup until something like 50 degrees C or three minutes after startup whichever comes first. So a cold tranny will not lock up so can not show sudden slip.

CalG

CalG

The current value always increases after a period of high slip!

(Decreasing values when entering over run conditions)

Example
:
at .44A and zero slip, then .488A at 320rpm slip, followed by .496A returning to zero slip and a closed TCC. These are at 500 ms time intervals.

Again: .416A at zero slip, then .424A at 128 rpm, then .456A at 192 rpm slip then .736 amps zero slip and TCC closed. again, 500ms time intervals.

This observation suggests that the TCM is trying to do something about the slip situation.

CalG

CalG

Two "mechanical" functions are beating around in my head.

First, If the TCC friction material has the wrong combination of stick slip characteristics perhaps due to hage heat and wear. Looking for other forms of control is hopeless. I am investigating this aspect.

Second: If the TCM has a fixed value of applied voltage for a given set of input conditions, with the assumption that applied electrical power yields equal fluid clamping force, then if there is leakage in the VB that either dissipates the hydraulic flow on the apply side, or restricts the out flow , this may lead to a decreased functional pressure. I can see the VB being an issue if the anticipated compensation is always with the system hydraulic pressure.

This goes along with the Sonnax information.


Has anyone had the opportunity to replace the VB with a factory fresh one?


More ideas from the experts ;-)
We know our own problems best!


CalG

CalG

Further down the spread sheet, are several examples of TCC solenoid current decreasing with increasing slip.

Example:

T1 .736A TC closed, 0 slip
T2 .512A TC active, 0 slip
T3 .472A TC active, 288 rpm slip
T4 .504A TC active, 192 rpm slip
T5 .736A TC closed, 0 slip

All at .5 sec interval and
falling Throttle PI 20, 16, 11, 11, 10

2.5 seconds from lock up, to slip, to lock up!

Further down, just moments after the example above there is a 7 second period of random current values in the .45A to .736 lock-up range associated with irratic slip values.

One episode has the current range between .488 and .52A with slip rpm from zero to 512, this with fairly even throttle position ranging between 11.4 and 9.8 Decreasing.

This display is confusing at present.

Back to work

CalG

PaulW

I recently had my transmission rebuilt.

1. With new friction plates, it acts exactly as it did before.

2. After rebuild, I put in a rebuit valve body from a 7 series BMW, and still had the hunting and thumping.

Therefore, I think it's an input signal. I replaced the internal speed sensor with no results also.

rompbogger123

I think it is great that we are investigating this issue rather than just living with it. Hats off to everyone trying to solve these problems. as far as the hunting goes i cant say i have any answers as to what causes it but is it possible it is in the tcm itself? could there be a certainb resistor that gets corroded solder joints over time. paul you said you put in a valve body from a 7 series? i had asked that question on here before because i was aware that the same transmission was used in those cars but it appears that it didnt fix youre problem. i think our next step is to use a bmw tcm and modify it to our cars. it seems as though we have tried everything else. paul did you also replace the torque converter whn you rebuilt yours?

CalG

Reading the inter- web,

The BMW drivers have transmission problems similar to ours. Certainly the THUMP.

CalG

ZRock

Wasn't aware that the Bimmers had similar issues. I was about to ask if anyone had considered dropping a 7er transmission into an A8 and essentially convert to RWD... or do the front driveshafts/halfshafts form a critical part of the front suspension?

TZ