PaulW

Okay, so this is now killing me!

Now I'm going to try a new transmission input speed sensor. It's mounted on top of the valve body.

<img src="http://www.audipages.com/Tech_Articles/auto_transmission/speedsensor1.JPG">

It measures the input speed of the transmission (i.e. how fast the engine is driving it) and there is also an output speed sensor at the back on the tranny that is external.

When Gabor changed from his 97 valve body with one from an 02, it stoppped hunting. However, it had the speed sensor on it from the 02.

When he put the 02 transmission in his car, it didn't hunt.....but then he had some unrelated problems and swapped valve bodies, he kept the speed sensor on each respective valve body and the tranny started hunting with the 97 valve body and speed sensor.

Since he had the 02 output speed sensor still installed, hopefully it can be concluded that it did not add to the problem.

So for $58, I'm getting a new speed sensor and going to swap it out.

It senses input speed, output speed is sensed by the other sensor, and the TCU compares the two and if there is a large mismatch (transmission slipping) it dumps it to Limp Mode. We think that's when a lot of the clutch baskets are ripping, when the thing revs and then it is dumped to limp mode and gets torqued to all hell.

<img src="http://www.audipages.com/Tech_Articles/auto_transmission/tran1012.jpg">

<img src="http://www.audipages.com/Tech_Articles/auto_transmission/tran1013.jpg">

<img src="http://www.audipages.com/Tech_Articles/auto_transmission/tran1014.jpg">

ex-a8drifter

you're still looking for a S8 after fixing up the A8? wow, you should have no prob selling it now.

escapA8

Will the hunt for the holy grail (= uber-solution for the A8's transmission problems) be over soon?

ex-a8drifter

pssst, if you do find it, keep it on the down low....thats a way to pump up market values!

PaulW

'cause I won't say anything and will charge $50 a pop for the answer!!!

That should help pay for the rebuilt valve body......

skiracer1313

Are we learning more about these tranny's than we ever wanted to know?

backdoc

Would this have any corellation with the fact that there is no hunting or thumping when the rpm's are kept to 2000 or better. This is what I have noticed with my car (97 A8). I don't get any thumping or hunting when my rpm's are at least 2000. That's why when I drive around town in fourth, it drives great.
Doug

PaulW

I don't really know.....I think it's a sensor that is causing the problem....but with Gabor's experience, he changed the valve body (which had it's own speed sensor) and it went away.

So it's the next thing to check.

And yes, the speed thing could effect it, was thinking the same thing.

However, I can still get the TC to drop out in fourth gear, just not as easily with higher RPM's, it takes longer.

NODES

Im hoping this is the last piece of the hunting puzzle.

MP4.2+6.0

then if you are going here, buy the $99 wiring harness too from Ericcson or a similar ZF rebuilder. I'm the guy who posts about the output side of the sensors. In my case, I had Ericcson at least test the input side. Honestly, I can't tell if they replaced it on the valve body rebuild or not. I know they replaced at least a fair # of the solenoids. I shipped it to them dismounted. It came back installed in position.

As you know, the harness can only be done when the valve body is dropped because of that connection to the input sensor. For another $99 and because the big connector where it exits the tranny case has been implicated occasionally for poor connections (and since in truth I broke a piece of a connector cover), I changed it out. The replacement seemed to be wired a bit more cleanly, had a bit more redundancy on some of the common jumpering on one side of each solenoid and the like, when comparing it side by side to my 2000 vintage original.

Do test your output sensor too...