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D2 - Transmission Gearboxes, diffs, drive shafts.

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  #1  
Old 12th June 2016, 05:24 PM
MikkiJayne MikkiJayne is offline
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Default Shudder in 3rd 1800-2200rpm

Hi all,

At long last my S8 is all back together and almost all behaving properly, apart from a weird shudder in 3rd gear when warm / hot. It only happens at light throttle, going up a hill, from 1800-2200rpm. A bit of throttle will clear it, backing off won't, and it doesn't do it in S because it will be in 2nd in the same places where it would be picking 3rd in D. It does do it in tiptronic under the same conditions. It doesn't do it from cold - it needs to be driven for about half an hour, although I haven't spotted the temperature it starts at yet. >45* I think.

Its quite a vigorous shudder - much more harsh than a misfire. No codes whatsoever- ecu, tcu and abs are all clear. It will throw the 11119 missing gear signal code in tiptronic, but that seems quite common. Other than the shudder it drives just fine, shifts smoothly (no thump), kicks down fine, pulls away fine. I've had a co-pilot watching vcds and there's no observable change in rpm, engine load, engine request, torque converter clutch, F125, or gear selection.

The gearbox has had the problem bearing and o-ring changed (although they were fine when I took it to bits), and the clutch packs looked fine. It took the full 9 litres of fluid when I refilled it at 35*. The tcu has been encouraged to re-do its basic settings since it has been disconnected for a while.

Any ideas please? I'm completely stumped and can't even find any reports of similar symptoms on t'interweb
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Old 15th June 2016, 09:52 PM
MikkiJayne MikkiJayne is offline
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So everyone else is at as much of as loss to explain this as I am then I guess!

I'm just going to drive it 'til it explodes in that case, then stick an 0A3 in it
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Old 16th June 2016, 06:21 AM
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Dezzy Dezzy is offline
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Quote:
Originally Posted by MikkiJayne View Post
So everyone else is at as much of as loss to explain this as I am then I guess!

I'm just going to drive it 'til it explodes in that case, then stick an 0A3 in it
Yeah you're right, lost. I think you broke it The 6 gang would impressive though in a rhd
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  #4  
Old 16th June 2016, 09:32 AM
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The problem is, Mikki, that you seem pretty sharp on the mechanical end with a degree of knowledge and hands on experience that exceeds most people on this forum - so, if you dont know what the explanation is, then most others may not be able offer much.
For what it's worth, my only offering is that it appears to happen under load (uphill, light throttle in 3rd) and can be cleared by gear/throttle change and is therefore more likely to be fuel mixture issue rather than mechanical.... maybe?
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Old 17th June 2016, 11:27 AM
Dave McB Dave McB is offline
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My old S8 used to do it until I changed the fluid and filter.

I suspect its the valve bodies not closing or connecting properly causing it to not choose the correct gear.

Do a filter change, check the levels and see how u get on.
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  #6  
Old 17th June 2016, 11:49 AM
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Engine sounds fine, and the gearbox otherwise shifts ok ?

So, how about torque convertor ?

It will try and lock up around 50mph when in drive.

In tiptronic, it locks up much sooner.

Does the problem happen in tiptronic, and drive ?
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  #7  
Old 17th June 2016, 08:07 PM
MikkiJayne MikkiJayne is offline
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The engine is glorious It shifts perfectly in all gears too, both in and out of 3rd. Its already in gear when it does the shudder, rather than shuddering as it goes in.

I *think* happens in both tip and drive in the same conditions but actually on the last test drive I was avoiding tip since it keeps throwing the 11119 gear signal code in the ABS. I couldn't quite follow what VCDS was telling me about the TC - it was open, closed, and re-something, none of which seemed to correspond with what I thought it should be doing. I'll try it again and report back.

DaveMcB - it has just had new fluid and filter

David'S8 - thanks for the compliment! If it was a 4 or 6 I'd be all over it, but this is the first time I've properly worked on an 8 or a 5HP24 so I'll take all the help I can get -fuel filter soon
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  #8  
Old 6th July 2016, 08:22 PM
MikkiJayne MikkiJayne is offline
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Sooo... took it out for a hundred miles or so today. The shudder happens in 1, 2 and 3 in the right circumstances - low rpm, light throttle, mostly up hill but not always and also happens in D, S and Tip. At one point pulling away from a stop up a hill it did it in 1, 2 and 3 in succession until I got annoyed and booted it. Lots of throttle and it doesn't do it at all - Tip or S on the twisty bits and it is perfectly fine (and wow does it move!!!). The shudder really spoils the experience though.

I am a bit surprised how low geared it is though. I knew the S8 had different ratios to the others, but 3K at 80 seems a bit excessive for a V8. That's about the same as the TT 225 whereas my 3.7 was geared the same as a diesel. The gearing is quite an incentive for a manual conversion whether the auto goes bang or not...
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Old 13th July 2016, 10:54 AM
MikkiJayne MikkiJayne is offline
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Having thought about this a bit more I've realised that the problems really started when it was low on fluid before I took it out. The gearbox sump had been fitted with bathroom sealant so it was ****ing oil everywhere. I only checked it when I pulled the drivetrain, but it was whining quite badly just before that. The oil level was down to the join between the sump and the casing so I'd guess about 3 litres short.

I'm wondering if this did some permanent harm to the TC before I even took it to bits, and so whatever I've done afterwards has actually had no effect on the underlying problem.

Given our sponsor's online sale, is it worth sticking in a used TC before I tear it all apart again? At least I can drive it while I collect manual conversion parts then...
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  #10  
Old 13th July 2016, 05:26 PM
MikkiJayne MikkiJayne is offline
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Well I bought another TC in the sale. Barring any bright ideas to do with the valve body I'll make a start pulling it out next week.
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