Dean_Fuller

Background is TT was making a rattling sound. Vibration at highway speed so I assumed the TT bearings were gone even though I have records that a rebuilt TT was installed in 2002. One would think you can get more than 10 years out of a rebuilt TT ? ? ?

Anyway...I started the TT removaly a couple days ago and finally today got in out to see.

https://rennlist.com/forums/attachme...1&d=1353449164

I then measured the rod projection are the front of the tube.

https://rennlist.com/forums/attachme...1&d=1353449398

I then removed the rear coupler and TT bolts to seperate the TT from the trans. What happened was the tube slid out leaving the rod attached...not good as the bearings should be tight enough to hold the rod in place. Now i see why the rod was moving all over the place.

https://rennlist.com/forums/attachme...1&d=1353449593

After the tube was loose I turned it on end and the dampener FELL out. I removed the other 2 ( yes...just 2 bearings) with very little effort. This is all that was in the TT ....

https://rennlist.com/forums/attachme...1&d=1353449739

I NEED to know how this happened so it will not happen again...Is this the correct TT and rod for a 1989 s4 auto??? How many bearings should I have?? Here are details of the rod that I have.

https://rennlist.com/forums/attachme...1&d=1353449842

https://rennlist.com/forums/attachme...1&d=1353449888

Any help whould be very appreciated.

Dean_Fuller

I can figure out how it insert pics in text yet...sorry.

Landseer

Then concentrate on the text.

What exactly are you asking?

ROG100

There should be two bearings in an 87 to 95 auto IIRC

Dean_Fuller

I NEED to know how this happened so it will not happen again...Is this the correct TT and rod for a 1989 s4 auto??? I have never seen this happen before. I sure don't want it hapenning again.

Dean_Fuller

I can't even find the 2 carriers for the dampener. It was just loose inside. May have been part of the rattle sound.

Black Sea RD

Hi Dean,

From the pictures you have a rebuilt TT that used old bearing holders, old bearing inserts and the old vibration dampener. The only new pieces are the two incorrect bearings placed into the old bearing housings.

Up to 1987, 928 automatic TTs used a 25mm drive shaft with three bearing units and a vibration dampener from the factory.

Sometime in 1987 and up through the GTS models, 928 automatic TTs used 28mm drive shafts with only two bearing units and a vibration dampener in them from the factory.

This TT was rebuilt with an older 25mm drive shaft instead of the newer 28mm drive shaft which are more prone to shear fractures. This is a good thing. But the re-builder should have placed three bearing units in the TT when using the 25mm drive shaft.

As far as the vibration dampener, anything rubber will fail with age. This vibration dampener has come apart as many are doing due to their age.

Hope this helps,

Hilton

Dean - the shaft in your pictures is from an early car (it has the groove for the circlip).

In '88MY, the shaft diameter changed to a 28mm shaft with a neck-down to the same spline size where it enters the transmission. It is however generally acknowledged that the thicker shaft is inferior as the neck-down creates stress risers and those later shafts are prone to shearing in two.

Also, Auto has 2 bearings, Manual has 3 (both auto and 5-speed have the vibration dampener - except for Clubsport/SE/89GT models AFAIK).

I'd measure the length of your shaft.. if its the correct length for 80-95 (per the diagram below), I'd keep it.

Here's a handy pic by Erkka on measurements:

Landseer

If you were to decide you need an original (needs rebuilding) 89 TT, I do have a spare.

WallyP

If you have not already done so, I would immediately get the driveshaft out of the rear coupling. If that weight that is cantilevered out from the coupling manages to break the coupling, you have just spent some unnecessary money.

Ethre

For reference Dean, from Erkka's thread:

Dean_Fuller

The drive rod at rear changes size...is this normal?

Ethre

Dean,

The spline ends on the left do not appear in a similar comparision picture from Constantine's website.

Mrmerlin

the last picture looks like the drive shaft is too long and has been pushed rearward this grooving the shaft into the input collar of the transmission.
It looks like a mismatch of parts has been used on this installation.
WARNING do not let the driveshaft hang unsupported in the input collar of the transmission EVER...

I have 3 bearings in my 88.
You need a good used damper as well,
and you should consider pinning the ends of it after its installed.
Quite possibly you also need a new correct driveshaft

Black Sea RD

Dean,

The drive shaft end you are showing has been forced into the rear coupler and now has dents from that encounter. These dents can manifest into a failure in the future since the metal has been compromised. Other than that this is a normal 25mm drive shaft that will fit in all year 928 automatics.

We do not advocate using another vibration dampener since they will fail, even if you try pinning it. Pinning might stop it from sliding around, but the heavy metal portion will still slop around and also ride on the drive shaft after it breaks away from its rubber holders, like yours did.

Our website has some more useful information on all of this information. We have invested a lot of time into looking at all the failures of the 928 and 944 drive lines which we have put on our website to help owners such as yourself.

Best regards,