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possible cause found for the gearbox issues


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In my lurking around TSN and other fine Audi sites i've seen many tales of woe of the gearbox hunting problem, the solution being either replace the gearbox or keep replacing the fluid. I don't recall ever seeing a cause for the problem. frown.gif

Buried in ELSAwin i've just found the stuff below - hope this helps someone and it shows that Audi are aware of a problem...

Technical solution

Problem description

Vehicle jerks at 1200-1600 rpm during the torque converter control phase.


Because of a missing water drain valve in the plenum chamber below the air conditioning unit water runs out onto the gearbox housing below. The water can get through the gearbox ventilation into the ATF caus-ing running problems.

Production solution

Extra clip on the water drain valve from 25.09.2000, Chassis No. 4D 1N 004497

Service solution

Check the ATF. If it is very milky, the gearbox must be replaced. If the water content is below 0.5%, change the ATF twice. Then drive the vehicle for about 3 to 6 miles after every change. The oil pipes and the gear oil cooler must be carefully cleaned. If the water drain valve is missing in the plenum chamber (above the gearbox housing in the body), it must be fitted.

Bond the drain valve to ensure its permanent attachment.

Before fitting the rubber valve in the cut-out of the plenum chamber clean the contact surfaces and then bond the rubber valve with universal bonder D 001 200.

Accounting instructions

Service number/damage code/manufacturer: 5155 018 ...

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Interesting find! 169144-ok.gif

I don't recall seeing any milky fluid in the various pics posted or the cars I have personally worked on, but sorting that drain valve out has to be a worthwhile piece of preventative work, nonetheless.

Excuse me, I've suddenly got something new to fiddle with on my car...

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  • 2 weeks later...

Took my A8 4.2S to Chester Auto Gearboxes (01244 537070) where for £160 inc VAT they drained ALL the oil out,flushed it and refilled with Audi oil and a new filter. Gbox much smoother again. They have a device to pump / suck ALL the oil out of the torque convertor. Previousley I've spent £300 with Audi doing 2 drains of around half the fluid after a filter and strainer change.

Interestingly I pointed out the advice from Audi that the Oil in the box is life long. They simply asked why does Audi's oil come marked up with a dated 12 month shelf life then? They recommended a yearly fluid change to ensure smooth running and spot any problems early before they become expensive by checking for metal and contaminents in the fluid. Makes sense to me with 152K on the clock.

They charge around £450 to remove / refit the box and then its parts and labour dependant on the fault. Thought you should know.

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and then what about this? Is this the shunting that we all talk about:



4.2 97/99 Engine jolts in driving direction at low engine speeds Replacement gearbox control unit (100 927 156...) with higher-set converter clutch regulation and traction shift-up set for higher speeds from 4th to 5th gear. See API 5/98. 90% confused.gif

because if it is the TCU cost £850+ VAT frown.gif

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@Ska: Ah ha! That sounds like a proper fix for the shunt/thump which occurs at 40-50mph on a closed throttle. Changing the revs at which the torque convertor locks and unlocks would make sense.

What I want to know now is (1) where did that come from and (2) can we get the gearbox control unit replaced at reduced/zero cost as it seems to be an inherent (i.e. designed-in) fault?

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It came from the Elsawin data base, in the section as the the other fix. Its as if they have logged the complaints, so they know there is a design fault and just hoped that when and if a customer has this fault they'll charge them for this fix sportifs2.gif

I would love it for them to replace the TCU for free but at £1000 a pop retail price covering 97-99 models do you think they'll do that for cars that are now 9 years old. Looks like they've fixed this for cars on 2000 plates; would be interesting to hear from any 2000+ A8 owners if they had these dreaded symptoms.

Another point 2nd hand TCU's could set you back from anywhere between £50-£200ish if anyone hears of a dead 8 in a scrapy then they should let the folks on TSN know, unfortunately this might be the only recourse frown.gif

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Unfortunately I suspect that you are absolutely right about the fix - why admit to a problem when your dealers can earn £££s to rectify it? ROLLEY~14.GIFopenfire.gif

Despite asking once or twice in the past I've not had any feedback from facelift D2 owners regarding this. The only facelift car I have direct experience of is low mileage and was still behaving perfectly before we changed the fluid as a preventative measure. The fact that it is an S8 also has a bearing because the shorter 4th & 5th gear ratios keep the revs that bit higher at the critical 40-50mph.

Any facelift owners care to comment? In particular I'd love to hear BumpRT's before/after gearbox experiences.

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Wheres this valve that drmnotorsport talks about and what exactly the Plenum chamber? Is that the black box with the ecu and tcu in it and how the phuck do you remove it cos the picis in elsa win may well have been drawn by my 5 year old smashfreakB.gif

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