DaveInSaltLake

(1998 A8, 112k miles)

17114 P0730

The car starts and runs pretty well. There's a bit of a delayed engagement of both D and R from N. It drove fine for a couple blocks, then when pulling away from a stop light there was the big bang/clunk in the tranny and it went into limp mode. Turned car off, limp mode disappeared for a few seconds, then was back with the big bang again.

The readouts from the trans Block 1 data windows were

in neutral:
1: 800 2: 800 3: 0 4: 1m

in drive:
1: 800 2: 0 3: 0 4: 1m

Tozo's post here: https://forums.audiworld.com/a8/msgs/127365.phtml seems to indicate no mechanical problem...but it's not exactly the same situation.
"If it goes into limp mode as soon as you put it in D (and the car hasn't moved yet)
hold the car with the brake, then check it with vag what is the engine speed in D(it should be 700-750rpm) and what is the input speed( should be 0rpm).
vag-com-transmission-measuring blocks-group1-display 1 (engine speed)display 2 (input speed) display 3 (output speed) display 4 (gear engaged). If it is 0rpm, then the tranny is fine mechanically."

I tried to run the same test on my 1997 A6 to compare but the data blocks are for different parameters. Should the input speed drop from idle rpm to zero when shifted from N to D?

Is the the classic broken clutch basket?

tozoM8

Broken basket wouldn't move the car at all. We had an 97' A8 with 68K miles in the shop this week with a broken clutch A basket. It was ugly. It broke clutch A-C-D-E. We had to buy a bunch of hard parts.

DaveInSaltLake

logged between D and N? 800ish rpm in N, zero in D.


Is that normal?

tozoM8

Yes, 0 input speed in D if the car isn't moving. The input shaft is locked (A clutch) to the drive train. Take your foot off of the brake and the TC will drag the input shaft and the car start moving. If clutch A is completely broken, it will not lock the input shaft to the drive train and it will spin with the TC. The input speed sensor is monitoring the A basket/input shaft.

DaveInSaltLake

from a ZF document:
<img src="http://i47.photobucket.com/albums/f174/DavesData2/A8%20Trans/5HP24Aparts3.jpg" border="0" alt="Photobucket">

tozoM8

That is the one. We have a collection of them in the shop.

DaveInSaltLake

the transmission into limp/4th without regard to rpm or load, thus breaking the basket under the right/wrong circumstances?

I could imagine that the 300hp the A8 produces would make it a much more common problem than the 175hp the 12V V6 I'm more familiar with puts out.

Or...is it due to one of the seals failing in the A Clutch assembly and ATF pressure forcing the basktet off center?

tozoM8

Slip means incorrect gear ratio and the TCU puts it into limp mode with full pressure regardless of rpm. That's when chit happens

DaveInSaltLake

Any way to recode the TCM or snip a wire between the TCM and trans? I would still like to see the Limp mode on the gear indicator display, but keep the trans itself from that earthquake of a jolt.

Seems that would save a LOT of people a LOT of problems.

tozoM8

It happens all the time, not only Audi. 90% of the cars in the shop has less than 100K miles. Automatic trannys break. Fortunately for us, used Audi buyers it results in a bargain price. I recently bought a 97' A8 with a broken tranny for $2900. After fixing all the problems and title, tax it is a $4100 car runs perfect.