CalG

do you recall the Amperage to the control solenoid at this slip value?

Or could you obtain fresh data for comparison. Excessive slip is not required ;-)

CalG

skiwi

i have run a trace and , as expected, the n18 current is pretty predictable.

0.048 with tcc "open", 0.416 with tcc "regulating", and 0.744 with the tcc "closed". there is never any change to the current in tcc "open" or "closed" states.

in the "regulating" state, there is a little variability with 0.408 as the floor, and a few blips up to 0.45 or 0.46. tcc slip during this time is <200rpm, the vast majority less than 70rpm.

to put it another way, of the time when the tcc is "regulating" (280 data points), the average current is 0.419amp, with a standard dev of 0.018amp

CalG

Periods of multiple events were recorded. But I tend to let off the throttle when hunting is innitiated. Still, three or four events in a 7-10 second time window is evidence enough of the pattern.
In a comparison with a properly performing transmission system, I am most curious to know if the TCC is commanded into TCR mode with the same apparent capriciousness.

The fact that the locked TCC does not slip under load suggests no absolute mechanical failures. But perhaps, a lot of little things.

Wouldn't a pressure transducer on the TCC apply tap on the transmission housing be a nice thing!

When I think from the point of view of the rebuilder, It is easy to point at wear,blockage and leakage, fluids and materials

When the TCM command responses are viewed I question the relationship of the many inputs. From my personal experience with electronic systems and components, I think there must be some power transister on the blink somewhere.

Taken all together, I can see why it makes sense to just put in a quality replacement transmission and start over. But then I read of the problems starting again at 60K miles and think that just is not OK Just what is the failure, Find it and fix it!

Satisfaction comes dearly at times


CalG

CalG

Why do those values seem so fmiliar ? ;-)

CalG

Please tell

What is the TCC status, Amperage and slip value at the recorded event just after the last (previous) TCC lock, zero slip event?

That seems to be the trigger point.

CalG

CalG

I log TCC open status at .144 amps, 3 times the .044 value you see.

Not significant from a functional standpoint perhaps. But......???
hmmmmm.

CalG

skiwi

instances:
1) 0.440
2) 0.408
3) 0.416
4) 0.424
5) 0.408
6) 0.408
7) 0.432
8) 0.408
9) 0.408
10)0.416

skiwi

the rs6 has a 280mm tcc, up from 260mm, also increased clutch pressure..

ttuling

Logs from nonhunting transmissions will confirm that. My 2001 works that way (though 2000+ TCMs and transmissions don't hunt), and as far as I know so do other automatics -- they either unlock partially or completely if you close the throttle.

But when it works right, it's subtle, with just one small smooth rpm change and no hunting around for the right amount of slip.

You're entirely right that the TCM is initiating the unlock and slip. It's not happening because of an uncommanded hydraulic pressure drop. It's happening when nonhunting A8s would do it. But why isn't it as smooth and subtle as designed, and how can the slip rpm get into endless up/down cycles?

I maintain that nothing at all need be wrong with the ECM, TCM, or their sensors to explain this, in a way that's consistent with the glimpses of your and other data I've seen. The problem could all be between the TCM and the clutch. No TCM change has fixed hunting, as far as I can remember anyone here saying. One valve body change did, one (rebuilt, whatever that means) didn't.

Here's an example of how bad mechanical reactions can foul up the best control intentions:

It's as if you're driving down the road, and want to correct the steering just a little to the left. There's nothing wrong with wanting to do that, just as there's nothing wrong with when the TCM takes the clutch from locked to regulating. It's what happens next that's bad.

Suppose your steering gear tended to stick when you weren't turning the wheel. You might push harder and harder to the left on the wheel (corresponding to N218 current dropping) but not get any response. Then when the steering wheel breaks free, suppose it turns 30 degrees (corresponding to too much slip) and that's too much. Now you're stuck putting increasing rightward pressure on the wheel (increasing N218 current) but the car is still turning left (slipping the converter clutch too much). When the steering breaks free and turns right, you'll probably need to push left thereby restarting the cycle.

Notice how this steering problem would not bother you when you have turned the wheel all the way left (corresponding to an unlocked converter clutch) or right (corresponding to a locked clutch).

If WK-V were binding in some positions, or there were leakage between line pressure in the middle of the valve and feedback at its spring end, it could behave like this.

Other hydraulic causes for unexpected responses, like a stuck D4 accumulator making the responses exceptionally twitchy (like steering your car with Boeing sized hydraulics with the feel disconnected).

I wish we could get a new, not rebuilt, valve body into PaulW's transmission. The results would either bolster or shoot down this hypothesis. I don't think it's the only possible hypothesis, just one possible hypothesis.

I'm done flogging this horse for now, and look forward to seeing what you find out.

Tom

ZRock

to finally figure this out...

but we didn't have much luck chipping in for a Xmas ham, so I don't think we'd ever collect enough for a VB.



(I have nothing constructive to add to this technical discussion, so I'll keep quiet now. I am eagerly awaiting the solution though- keep up the good work everyone!)