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C5 S6 reverse gear problem


Ive searched and googled, but there are couple of different things that can cause this problem. Just took one car to make it driveable again (stayed 5 years on one place), and changed the engine oil to fire it up. Now it haves the issue with the gearbox, it wont drive on reverse. On D there seems no issues, cant test it on the highway as it needs new brakes first, but it drives inside the garage fine on D. We pushed it outside, and as the gearbox oil gets little warmer its moving a little in reverse, but its likes slipping, RPMs are going high and just a little moving.
Didnt change out gearbox oil yet and there are no CEL (didnt checked the codes yet). I thought im going to search a little and make a thread, maybe theres no point to waste money on new oil + filter if the box is busted.
What to you guys think of that, is it a waste of money to try with the new oil or maybe its the reason (old oil or low level?)?.
From here ive found one problem:

Reverse Piston Failure

The molded piston that applies reverse gear has a tendency to fail on the ZF5HP24 automatic transmission, losing a portion of the rubber that forms the seal. This causes reverse gear to partially or wholly fail to apply, usually resulting in a loss of reverse gear. As with the above A clutch failure, if caught early enough it may be sufficient to just replace the faulty piston, however leaving the problem can (and usually will) cause other problems within the transmission.

Can it be the issue and if it is, is there some easy fix or point to fix at all?
Am i on the right way to change out the gearbox oil + filter?
Can i diagnose and look the gearbox work with the vag-com?

It does sound like the F piston.

No easy fix as it is buried right at the bottom of the box.
I doubt an oil change will help.
It is possibly a blocked/worn tube in the valve body or one of the small oil pipes which transport the ATF around, but my money is on the F Piston.

Check out my gearbox teardown thread in this forum. If you can do the work yourself it would be worth doing.

Okay, thats what i was afraid, that its a huge job. Im thinking of manual convesion then, used parts are cheap and it can be same amount of money than fixing auto box.

Added 2 litres of oil what was missing. From cold it was still slipping and didnt reverse, but as we drove around a little and the gearbox oil was warmer, it started to reverse normally. Like some klick there was and after that it was much better. Didnt cool it down and tested from the cold again but i bet its still the same, slipping from the cold. Forum Index -> Audi S6 & RS 6 (C5) quattro
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