gtreng1

My link to the original post is below. If you would like to participate, visit my site or e-mail me your info.

Name:
Contact Info: (Address, Phone, etc.)
VIN:
Mileage of first occurance or repair:
Description of problem:
Expenses so far trying to fix the problem:

So far we only have 8 people. Im hoping for atleast 30 before I send it off to AoA.<ul><li><a href="https://forums.audiworld.com/a8/msgs/141028.phtml">https://forums.audiworld.com/a8/msgs/141028.phtml</a</li></ul>

gtreng1

From the link below:

"I have worked on a rebuilt many of these A8 quattro units(5HP24A). They are a very heavy duty unit. The size of the gear train is about like a 3/4 ton truck. I have never seen a gear train failure yet. One quirks with this transmission is that audi constantly slips the torque converter intentionally about 20 to 60 RPM for drive ability purposes-in other words it doesn't feel like the engine is getting lugged down. The side effect of this is that the torque converters wear out and when you try to do a light acceleration the engine rpms will constantly bounce about 300 RPM's. The reason for this is that the lining is worn off the torque converter. I've tried to change the transmission computers in several cars and it didn't fix a thing. I also checked the throttle position sensor and it was ok. Many times there will be no trouble codes in the transmission computer. VAG-com software is great but it can't do more than Audi's computers allow it to do. Many times there are problems that drive you crazy but the computer says everything is ok and from what the computer sees everything is ok because it's within tolerance. There is one valve that sometimes also sticks in the valve body from all this clutch material going through it. There are couple things to really be careful when changing the torque converter. It is very difficult to find a high quality converter since they are a very difficult converter to rebuild due to the design. Sometimes you can lose reverse with this trans as well. The most common reason is a piston blowing out in the very back of the trans and you pretty much have the rebuild trans when this happens.

Be very careful who rebuilds this trans.
There are about 4 seal installers which are a absolute must. the trouble is the cost of these installers is so cost prohibitive that you wouldn't even think about buying them. I made them in my machine shop. Most rebuilders leave these seals alone and say that it wasn't leaking when it came in. I hate that kind of attitude. Do it right or don't do it at all. The reason these seals are so important is because there are actually three sumps in this transmission: Front differential; center differential; and transmission fluid. If they intermix it is big trouble and the trans won't last long."<ul><li><a href="http://townhall-talk.edmunds.com/direct/view/.ee9e503">http://townhall-talk.edmunds.com/direct/view/.ee9e503</a</li></ul>

CalG

There have been two instances of immediate "fixes" for the uncontrolled torque converter clutch symptom (hunting) by way of replacing the transmission valve body with a late model unit. No TC rebuild, No Transmission Control Unit exchange.

We must be careful of cause and effect.

It could be that the significant change is to rid the VB of accumulated debris.

How to tell?

I really should do a careful dissasembly and examination of the retired VB on now on the work bench.

Regards

Calg

gtreng1

..doesn't the dealer know these things. Being an Engineer, it ticks me off that this has gone ignored and unrecognized by the manufacturer, I'm sure they've known about it though. I was willing to accept these things when I bought the car b/c I feel its a near masterpiece in automotive engineering. Not all of us have endless pots of money to play around with. I just hate sinking $$ down the toilet on a diagnosis from an Audi tech that can't figure it out. Luckily most every D2 owner on the board is mechanically savy and likes working on the car themselves.

CalG

My feelings and your remarks are in line.

I Appreciate the rest of the car enough to accept the weakness. I am so grateful for information sources such as this list, Audipages Vag Com, Bentley's etc. My sympathy to owners less inclined. I feel that Audi has dropped the ball on the the application of the 5HP24 transmissions for A8 owners. But with a company philosophy of a 7 year "lifetime" what more can one expect?

Not allowing thier own service organization to gain useful diagnostic and repair information by directing all authorized repairs as "replace transmission" has been a benefit to no one. Why a hush on the information? The independent repair facilities don't see enough of these units to build a reasonable level of confidence at making repairs either.

We all know stories of the expense and difficulty of obtaining a "good rebuilt transmission replacement" Even the authorized ZF repair facilities only offer a limited warrantee.

Much good information regarding the mechanicals of the transmission has come to me through the BMW enthusiasts. Same hardware!, and I have never heard the word "Hunting" on those lists.
A softness in the Audi control systems then? But electronic upgrades may be out of the scope of a garage DIY owner/mechanic. And a software rewrite is expensive! I can understand Audi not wanting to undertake such an upgrade.

I am fortunate to have been on the receiving end
of a good effort envolving the Valve Body exchange. To date, all is well. I would like to drive a late model A8 to experience contemporary transmission drivability before I say my expectations are fully met. There is some shift harshness that I feel is out of character in the A8 class.

People like Tozo have done a lot of digging. If we could uncover additional practical knowledge and comparitives, perhaps we could make definitive statements of cause and effect. A well versed ZF transmission repair (not only exchange ;0) person would be a wonderful rescource.

I will continue to investigate these transmission units. Both in parts upgrade feasability and in evaluation of the VB on my work bench. With the car now working just fine, and the presses of job and family, progress may be slow.

We can all ask one another to keep the topic fresh until the options are known and available to any who care. No more money spent on diagnosis and "try this" fixes.

Sophistication has it's price.

regards

CalG