winy68

I'm also having some trouble with my 05 4.2 A8L's iddle or transmission. (I have a post on air suspension trouble) The problems are currently minor but I fear could turn into a major problem.

My mechanic has checked out my transmission and found no problems, and recently did the fluid change at around 110,000 or whatever the interval was as part of that service.

>>I should mention that I had the "hooting" noise in my transmission at around 60,000 miles which the dealer corrected (while still under warranty) by using a different transmission fluid, I think it was the blue type. I'm sure he used the same type of fluid.
<<

The problems:
When the car is in gear (D or R) and my foot is on the brake I get some vibration as if the idle is to low and the car is going to stall.
I also occasionally get a rough shift even when i'm driving gently.

Again my mechanic has put it on a computer and found no codes said the pressure and everything looks good.

any ideas what could be going on?
also worst case has anyone had to rebuild their transmission?

Thanks

mishar

Did your mechanic scan the engine too?

winy68

yes he did, didn't show anything.
I actually also just had the major service with new plugs etc, I was hoping I may have had a fouled plug but nothing...

He said she's clean

MP4.2+6.0

If I were to guess, like others I would think motor first (plugs, coil packs, maybe a vacuum leak, etc.). Next on the vibration issue and maybe even the shift sensation, I would think about the motor mounts. Many ignore the codes for mount solenoids, and a lot seem to have them now in their scans. Also, if you also lose the torque mount (up on the front passenger (U.S.) side of the motor), from my W12 experience anyway you can get some more perceptible vibration. That one does not have a sensor from my W12 experience, so you won't get a code like you might for the primary two mounts.

Last, I would say maybe deep inside the tranny. Having dove way, way in on that recently, could be in the solenoids in the valve body (Mechatronic) and/or its seal to the main tranny case. A ZF specialized shop can deal with that as piece parts with the tranny in car, rather than a full rebuild, but they need to know what they are doing. Those generally won't show as codes and I'm not aware of any definitive test to prove the issue is there or not ahead of time, but you will get increasing shift issues as a clue--maybe the hoot, maybe a flared gear miss, maybe a hard shift clunk, etc. As it worsens it may kick out to "SAFE" mode if you don't adapt your driving to try to avoid the issue--not the way one wants to drive a nice car anyway though! A fluid drain that does NOT show any obvious bits of clutch, metal, etc. is an indirect pointer it is not a classic worn out or broken physical tranny, but something more subtle like in these parts.

FWIW, even though the 6 speed was also used in related flavors in tons of Audis, I could find very little about it. It is a very reliable tranny as they go, nothing like the comparative long term lemon five speed from the D2 that seemed to (un) reliably and pretty seriously fail at right around 100K. I get the sense there is almost no DIY serious wrenching and deep diagnostics going on for the D3 or Audi's more generally like there was back for the D2. If you tediously search, you can find some overlapping relevant info (including forum posts) for the very similar ZF six speed (RWD) fitted in the V8 BMW's, and some manufacturer type info from Jag and even Ford (Europe) and Hyundai IIRC. Often the earlier info is about the same "hoot" as Audi found (and Audi's TSB is as good or better than the others), but some of the BMW threads in recent years get deeper into the Mechatronic area.

Last, on the tranny, you can also try an adaptation to have it relearn its shifting. It is documented for how to do it toward the end of the hoot TSB; you need a VAG COM/VCDS to trigger it, then to run through a fairly precise driving cycle that takes about 30 minutes on a quiet mid speed road. I suspect in the real world a lot of dealers probably just trigger it and then drive it around some with a gentle foot; to do it "by the book" requires very long and gentle acceleration and then coast downs from 1 to 6 to 1 several times. It may help with shift quality issues, or it may result in very little difference unless you get deeper inside.

dvs_dave

Interesting post here from a Lincoln Navigator forum. It uses the same ZF 6HP26 transmission as our A8. Basically he did a full DIY fluid change for 70 bucks (Mercon SP is the same as LifeGuard 6 but a fraction of the price) and then went on to put new seals in the valve body.

http://www.ford-trucks.com/forums/1081568-06-navigator-6-speed-zf-automatic-transmission-fluid-change-procedures.html

Panelhead

Are you sure the Mercon SP is the same as LifeGuard 6? This cuts the cost of a fluid change in half.

mishar

Quite a few of us did it on our A8's. It is a bit more difficult since there is no filling plug and it is much lower car. Generally it included dropping the pan and replacing filter and the seal, but it could be just flashed with 5 liters of fresh ATF. Actually I would recommend exactly that and done by oil shop. It is easy and inexpensive so it can be done more often. Changing half of ATF every 30-50K miles is much better than recommended fill for life.

MP4.2+6.0

No one knows, and ZF doesn't confirm it, nor as I recall do shelf brand fluids like Mercon tie explicitly to the ZF spec. Frankly, you can go buy the Hyundai fluid too, and I bet for a Hyundai instead of Audi price. Hyundai's documentation on the 6HP is actually pretty good. But, would you seriously pour (pump) Hyundai fluid in your tranny? Virtually the identical question used to be debated on the preceding generation 5 speed on the D2 forum and w/ the C5 A6 4.2. But since the tranny often blew up at about 100K, who knows if the real or alternate fluid even mattered. Fortunately, the 6HP isn't doing that and the internal design issues on the C5 eventually got understood--weak clutch basket and some other things.

Regardless, only about 5 grand if it comes out wrong on the fluid guess, but probably 90% chance it will all be fine. Kind of Tranny Russian Roulette, with say a ten shooter to improve the odds to make it interesting. Take a spin... Mercon, Hyundai, whatever. For me, unless it has the ZF spec compliance documented, non starter. As I recall Jag and BMW both do.

Having now seen the inside of the tranny myself, the fluid change to start often makes sense. Pick the weapon of choice for that. But, don't be surprised if in the presence of shifting issues it's not a cure all. As I have posted before, there is a weak rubber part inside that has been documented in BMW's and that I personally found in mine at an earlier stage, and a change in internal metals (no more lead compliance) confirmed by a leading ZF distributor that makes longest term wear a further TBD. But against the long term wear issue, some fluid change definitely makes even more sense regardless, and the path I am continuing on as well.

For those interested, my prior post/reply on this, with the confirming picture: Separate and Combined Trans Fluid Systems?! - AudiWorld Forums

dvs_dave

Yep. Some guy on bimmerfest actually got Mercon SP and LF6 samples chemically analyzed by Blackstone Labs and aside from color they were found to be identical. Plenty of examples out there of the less precious A6 boys putting Mercon SP in with zero issues long term. Who'd a thunk, huh?
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"The result is that Mercon SP gave the same results as LifeGuard 6

From Blackstone:
This sample of Mercon SP looks very similar to the Shell Lifeguard 6 sample. Note that both oils
contain calcium, phosphorus, and boron as additives, but this sample of Mercon SP contains just a little bit
more of each element. The viscosity of each sample was near exactly the same. No moisture, insolubles, or
wear metals were found in either sample. Both the Mercon SP and the Shell Lifeguard 6 should work well for
you as automatic transmission fluid. The Mercon SP is red in color and the Shell Lifeguard 6 is gold, but the color should not affect how these oils perform.

This sample of Lifeguard 6 uses calcium, phosphorus, and boron as it's main additives. The
viscosity read within the normal range for ATF oil and no wear metals, moisture, or insolubles were found.
The comparison between this and the Mercon SP ATF's additive package is about as close as can be
expected, though not exact. The additive packages are similar enough that they could possibly be from
different runs of the same fluid type. The only real difference was that this oil was gold in color whereas the color should not affect how these oils perform."
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See here for more:
http://www.bimmerfest.com/forums/archive/index.php/t-441992.html

winy68

Thanks to MP4 and all other input on this topic.

I'm disappointed no-one could give me an exact, precise diagnosis with the amount of information I provided over the internet


Good info to know on the fluid
As I recall that fluid cost me about $40 per quart and I needed about 7 quarts. (As I remember I got that at a discount as well)