heinrich

Thanks Brendan

Vilhuer

This is waiting to get out from rear end of '90 MY S4 tube.

heinrich

damn

Vilhuer

For some reason factory put vibration damper behind last (2nd or 3rd) support bearing on automatics and so close to torque converter input.

BC

Erkka - How would we make that 30mm front increase with a 78 box and the choice of 86 or 78 TT?

Vilhuer

Not sure if I understand your question. If you want to use '78 box you need to use '78-79 TT as rear clamp bolt is in different position. Also rear subframe is different.

BC

Will that make the entire position further back then if I used some other combination?

Vilhuer

Front end of G28.03 is about 30mm further back than in later manual gearboxes. As it is difficult to mix '80-95 TT and G28.03 you are stuck at using '78-79 TT also unless you want to make new bolt groove into TT center shaft. If you don't want to do that and use later TT tube this in turn means you have to use same period rear subframe and arm from selector lever to coupler at gearbox to take up 30mm difference. Also you need to add mounting point into TT tube for front lever support unless you want to bolt it into body like it was in '78-79 MY. Only G28.03 compatible tube which has mounting point for front lever support is early '80 MY 4.5L tubes. And early '78 MY TT has shorter clamp between clutch shaft and TT center shaft. This only affect first 54 US '78 cars though. Its a minefield...

BC

But a fun minefield.

I have the shaft right now almost out of the 78 TT. Sunny and 80 in San Diego, great day for working with the garage door open, breezes pass by.

I have the 78 transmission (though it is the one with the different 5th gear sycnhro size, so maybe a late 78 - its past the *IIRC* 1119 trans number or something similar. nearly rebuilt with all new synchros, and 2 selector rings, and 5th selector now on r/1. I had fogotten about th 30 mm thing, or actually had thought without checking that it was 78 that was 30mm FORWARD.

I wonder what 30mm does to the olar moment at turn in.

I wonder if simply taking out other heavy things from the back of the car would offset that.

Its going into an 86 (with 86 half shafts attached to the 78 trans) behind an S4-like motor that will see an SC in its future, so I hope it all works out (fits).

Erkka - do you think I need continue using that thicker trans mount or can I substitute it for the regular one for that side?

Vilhuer

Reason Porsche changed to shorter TT was to move gearbox forward and gain better handling. So there must be some effect on moving it backwards.

Think mount on drivers side was just to counter heavy battery mounted into end of gearbox at '78 MY. Its overkill in any other MY.

'79 yearly changes document has interesting comment about TT bearings which I have missed previously.
The long drive shaft has been shortened and runs in three bearings (previosly two bearings).

Vilhuer

Update to old thread as have late automatic shaft and vibration damper under work.

Side by side comparison of '88 S4 manual and '90 S4 automatic TT internals and how they are positioned. Gearbox at left and engine at right, from top to bottom row:
- '80½-95 5sp outer tube
- '83/84-95 automatic outer tube
- '78-95 three 5sp center shaft bearing supports and '82-95 vibration damper
- '91('90)-95 automatic vibration damper and two '89-95 center shaft bearing supports
- '80½-95 25mm 5sp center shaft
- '89-95 28mm automatic center shaft

'89-95 automatic bearing support look the same as '78 5sp, '88 S4 5sp and '92 GTS 5sp supports but all critical dimensions except width is different. Bearing type is 6007 and it has 62mm outside and 35mm inside diameter. Plastic inner piece is similar to 25mm support version that it has metal tube against bearing inner race and plastic against center shaft.



Does anyone have pictures of other style bearing support which is found on some automatic shafts at least? The one which is made out of two pieces and that need to be separated to change bearing.

'88 S4 5sp and '90 S4 Aut. dampers.

Factory documentation mention damper change for '91 MY S4 automatics but same year GT still used old style part. It seems at least some late '90 MY S4 got new style already as I believe this tube to be original for car it came from.

In another thread BrendanC says his damper has sticker with 72Hz and 20.5 degrees. I have also heard damper with 64Hz in it but do not know it it had any degrees number on too. What are these exactly and what should be done with the info while puting things back together?



'88 S4 5sp at top, '90 S4 at center and '92 GTS 5sp at bottom.

Manual GTS seem to use different damper than earlier 5sp cars. Maybe factory didn't see the point in doing two separate style parts when 5sp production numbers were so small.

Interestingly neither of the two late style dampers haven't got sticker on. What ever factory used those Hz and degrees numbers they must have changed something as stickers were nowhere to be found, in these two cases at least.

Late early damper is little over 15cm long where as new style is little under 14cm. Interesting '90 S4 and '92 GTS cast parts are slightly different while they have same part number in casting. Both weigh either same or very close to same and also have same dimensions. All three in fact have same critical measurements except lenght.



If I calculated right, both style damper castings do have enough large inside hole so that if rubber supports fail center shaft will not have to carry dampers weight. Outside is 84mm and inside 38mm. With 28mm center shaft its very close though as there isn't any spare room at all. 25mm shaft leaves 1.5mm empty space.

Vilhuer

Explanation why damper was added from '82 MY yearly changes document. Will this make any more sense to Hz and degree numbers?

heinrich

This has got to be the most informative thread I have ever read. Thank you so much for sharing Erkka.