Chrisindominican

i bought this car with 148k kms, and it had no reverse. I had read that this was common on these cars and generallly a seal in the reverse piston so I immediately took it for a rebuild. The shop broke part of the vacuum system on the front of the engine and I showed them when I was checking the car one day. It took ages to get the car back as they advised me if had a bad TCM, when I went to get it they said I could limp it home and search for a TCM and then come back. After a day I noticed that they had not fixed the vacuum part that they broke and obviously this was a problem, so I put a new piece of wire on it to make it work and assumed the TCM was not the problem. It seems the tranny suffered damage in this time and I lost reverse again. I took it back to the shop for them to rebuild again and now they want me to bring the new TCM to install and I am telling them it was the vaccu issue that was the problem. Is there some way to know for sure if it is the TCM and is this a common issue? The car has spent it life in the Caribbean and is in very clean condition except for this nagging problem. Thanks

ocles_inc

Wow, how frustrating. In my experience you can totally remove the TCM and have it sitting on the back seat or in your lap or on the sofa at home, and even so your car still should be able to drive just fine as to reverse (though the shift into reverse will be slightly more jarring). That's true for an A6 with this transmission and I have no reason to suspect the A8 or S8 are any different.

I don't understand the specifics and implications of the vacuum issue.

As to the TCM, on your car it should normally be located on the passenger side of the car under the cowl, easily accessible. I suppose water could have gotten into that area and flooded it out but you can probably inspect it quite easily and see if there are signs of water in that area.

Does this help?

As a more sobering observation, some shops are clueless as to the ZF 5HP-24A transmission and its issues. I love complexity and I know cars and computers yet even so it took me close to two years of messing with these cars and parts to finally have a functional level of understanding, It's an uphill battle for an A8 owner unless there's a good shop around, or unless (s)he is willing to get immersed into the technical issues and to methodically work each one. With an S8 that's probably worth doing.

Let me know how I can help more.

~Tanya