troverman

Two weeks ago, on the way home from an hour drive south, our '99 A8 4.2L would suddenly barely move away from the light at an intersection. I noticed the gear indicator in the screen showed all gear selections lit. Pulling over and restarting the car cured it for the ride home. However, in subsequent days the car did it again. A restart again cured it until 3 days ago the car experienced this same problem just pulling out of our street. Restarting would only cure the problem for a few seconds before all the gear selections lit again, and the car wouldn't go forward. We got it back home by driving in reverse.

So, reverse works totally fine. If you start the car and put the transmission into Drive, you feel first gear engage but then right off the car will barely move and all the gears light up.

How can the torque convertor be junk if reverse works fine? Fluid was changed around 10k miles ago at a cost of over $600. The only issue the trans has had is hunting between gears during certain speed ranges, but it has always done this. Car has 100k miles on it now.

Nollywood

First thing to do is an OBD scan. Hopefully it'll be something inexpensive to get fixed. I would have said something to do with the trans service - incorrect oil grade, incorrect level etc, but 10,000 miles is a long time for faults to remain dormant. That's almost a year's worth of driving.

tozoM8

It has a broken clutch A basket, you need a rebuild.

troverman

Tozo,

Is that literally the only possibility here? What about the F125 switch? I mean, it did this before and restarting cured the problem temporarily. So I can't see how:
Limp Home Mode = Transmission Rebuild

Maybe I'm just in denial. I know you're pretty experienced with this. Why does the clutch basket break? Versus say another vehicle with an auto transmission that lasts much, much longer. Is it a bad design?

Thanks

silverd2

I personally have never had ANY auto trans make it past 155K miles (VW)...some as early as 90K (VW). My only (of 3) Porsche 928S4 with auto trans went on me at 120K...that trans was built by Mercedes...Porsche never developed their own auto for 928's.

Anyway, once again: Have had the codes read? If it was electrical, the right code(s) would indicate that.
But, from what I've learned, Tozo is stating correctly that you are describing a broken clutch A basket. Even a failing basket can "work" for miles, before limp mode kicks in. Limp mode will kick in, for protection, well before the part completely explodes, just to get you home on what's left...and maybe less parts needed for the rebuild.
VW/Audi used to call it "Limp Home Mode" for a reason.

The pre 2000 ZF trans's (as I understand) had some weaker (thinner) parts in em than later models.

It is what it is and it sucks, but what can you do?

tozoM8

It cracks over time. The more it cracks around the more it slips and eventually it stops moving.

http://audipages.com/tozo/cracked%20clutch%20A2.JPG

troverman

Last night I put the car up on ramps. It took 4 tries just to get the car up on the ramps...1st gear would engage for a second, then limp home would engage. If I moved the car very quickly after starting, I could finally get it up on the ramp.

I checked the F125 connector plug. Pretty dry, some very mild corrosion. After cleaning and reassembling, there was absolutely no change in the transmission's behavior.

I noticed another, slightly larger multi-pin plug that appears to come from the trans pan. In getting this plug apart, it was literally dripping with engine oil (this A8 has plenty of engine oil leaks!) I cleaned as best I could, but it was not a good job. The immediate affect was that the trans operated normally. I drove the car for 3 miles and it drove completely normally. Halfway back home, limp mode engaged at about 40mph. Driving at this speed was fine but at each traffic light, I would have to restart the engine, get the car quickly into drive and it would pull away normally for a few seconds before going back to limp mode.

Can this plug cause this problem with a bad connection? Does this plug control the valve body? When I have a bit more time, I'm going to clean the plug with a degreaser and than apply some electrolytic paste to the contacts and see how the car behaves then.

silverd2

That would be the valve body wiring harness plug. If you're very lucky, you may be onto something(?)....all shifting, TCC control, main pressure control and ATF temp sensor.

Yep, compared to 40V engines, 32V's leak like a hemophiliac in a nail storm

An OBD scan (maybe even a cheap home scanner) should give you codes relating to that harness or sensor/ solenoids attached, if that;s your problem.

troverman

I'll scan it...no vag-com, but I do have a several hundred-dollar OBD-II scanner. I just assumed no MIL, no codes. Keeping fingers crossed...

silverd2

Are you sure your check engine light is working? It should come on as a test with ignition switched on, but engine not running.

In a '99, it's actually a changeable bulb (LED in later models) that can burn out...or be removed by a sneaky seller.

Yep, I have an $80 code reader that will only read and erase codes that trip the CEL. Many trans codes will trip a CEL.