Originally Posted by
rollerton
Except that VAG had originally said that the fluid in the trans is "LIFETIME" fucking fluid. They TOLD customers that the fluid need NEVER be changed. Sounds ridiculous but true. I have no idea if they ever corrected that policy..but I can even find it in print somewhere.
Lack of fluid change can have an effect on some failures, typically the torque converter issue on the 5HP19, but not the most common ones associated with the 5HP24A used on the V8's. The 2 most common failures are the lost of reverse gear (caused by a loss of ATF pressure) that will get progressively worse as the seals in the F clutch continue to leak and the dreaded clunk on shift. The latter is caused by a failure of the snap rings on clutch basket A that hold the clutch packs for forward gears 1 through 4. That failure was due to the design of the basket itself as the original part was a pressed metal that eventually would fail. That clutch pack routinely sees pressure spikes of 300 - 350psi and as the clutches are about 10" in diameter the snapring sees forces of 4000lbs on a regular basis. As you can see in the right side of the pic below, the basket fails where the snaprings clip in. To address this issue ZF moved to a CNC'ed part in later production runs and the replacement market which is part of the reason why you see comparatively fewer issues with this transmission on the facelift V8's in the C5 line. No amount of ATF fluid changes can every protect against these kinds of mechanical failures.
This pic was the failure on my old 2000 4.2L A6, however I had the same issue on my S6 just before Christmas this year.
Originally Posted by
rollerton
And #2 . When they build a 'high performance' version of one of their cars I think they should design the parts to withstand whatever daily abuse they might see.
These transmissions FAIL...and in a variety of ways. It's not a common single part. (except the TC seal on the 5hp19).
I flat out tell people who are potential buyers of these that the transmission WILL fail and to prepare for it; worst case is they're prepared for something that never happens (but it ALWAYS happens).
Agreed, however the design of the transmission was not an Audi problem as it was not spec build for them by ZF. ZF designed the 5HP24 for use in a wide variety of European sport luxury vehicles w/ a V8. It was found in various Land Rovers, the Jaguar XJ8, BMW 540/740/X5 as well as the C5 A6/S6/RS6 and D2 A8/S8. Audi only used it on the C5 and D2 platforms then moved to the 6speed version for later models. As you mention, the 5HP24 experienced a reasonably high rate of failure in all those applications.
The positive is that ZF has addressed the design flaws that contributed to the failures so a modern rebuild done by a reputable shop using ZF replacement parts will result in a transmission will out live the car. The negative is that the rebuilds are bloody EXPENSIVE, and most of it is in labour. The 5HP24a is a BEAST of a transmission, it's huge and heavy (160kg or 360lbs) so it's very difficult to get it in and out of the vehicle. For illustration for the others who've never seen this transmission (I know you have), this pic gives a good idea of the size of it.
It's from this is a really good thread that details the rebuild process in a 2001 S8:
http://www.motorgeek.com/viewtopic.php?f=15&t=46685
The cost of parts for an auto-rebuild is more or less the same as the cost of parts for the 6MT swap, $2347.59 in my case including all fluids. The labour is the killer; the labour bill on my recent rebuild was 12.7hrs for re&re and 13.8hrs for the rebuild itself. If you have the space and time to do the swap yourself it's a no brainer, if you're paying someone to do the wrenching for you it's a bit less clear cut. If you bought a swap-on-a-pallet from Scott @ AdvancedAutomotion you wouldn't be paying bench labour for the rebuild, however I'm sure the re&re labour would be more as the shop would have to be deciphering the swap instructions and swapping out drive shafts, trans mounts, half-shafts, etc.
I still wish it would have made sense to do the 6MT swap in my S6, especially after the rebuild came in $1K over what I expected and the shop confirmed they would have done the swap for me. However with the state of the CDN dollar vs the USD at the moment I would have been looking at $3800 + shipping to Canada + import duties and charges just in parts for that swap. Add it all in plus labor and the swap would have come in north of $6K so even going $1K over estimate the rebuild was the better option for me :(
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