Bill Ball

Greg, I appreciate the comment. I'm re-weighing my options. And re-weighing again.

New information....

I got the shaft out using a bottle jack and some wood blocks as a ram. Man, that shaft was TIGHT in the bushings!

What broke was NOT a bearing carrier - it's the damper. It was at the REAR of the shaft, with one bearing in the middle and the other at the front. The front bearing (and carrier) stayed in the tube. The middle bearing came out with the shaft, while the carrier remained behind. The bearings are still in good shape. This TT has never been worked on or replaced. So, I think In theory I could forego the damper and install a 3rd bearing and carrier at the rear (I've been offered one). Considering how TIGHT the bushings are on the shaft, this could be a bear to get right.

If I install the rebuilt TT from 928 Intl, I'm not sure I have a good core, in which case I'm out an additional $300. The bearing carriers do look good and the shaft is good as well as the tube, but the damper is toast. I will add that I opened up a rebuilt TT recently on another car and there was no damper - just 2 bearings - and that TT worked just fine (no vibration).

I could rebuild my TT with Constantine's Superbearings and sell the 928 International rebuilt TT locally (I know someone who wants one). That will take more time and money.

Thinking....

In the meantime, the rebuilt TT is on its way.

I the first picture below, you see the damper with its rear carrier broken into 3 pieces. The core of the broken front carrier is still on the damper. The outer shell of the damper's front carrier is still wedged in the TT. In the second picture, you see the second bearing still on the shaft. It's remarkable that tbe bearing, which is pressed into the carrier, came out with the bushing instead of staying behind with the carrier. Just shows you how very tight the bushings are on the shaft. It moved a bit down the shaft as I was pushing the shaft out of the tube, but then broke free of the carrier.

Bill Ball

This is very informative... Indicates automatics have the damper behind the two bearings, just as I found it. Indicates it is tuned to dampen vibration at 3300 and 4200 RPM. I should note that after I reinstalled my transmission recently, I started to notice my shifter vibrating at about 3000 RPM. Never did that before. The auto shifter is not mounted to the TT but to the tunnel above it. I tried shimming the shifter pivot shaft. Helped a little, but it still vibrated. Now I know why. Still, I'm going to try rebuilding with 3 bearings instead of the damper, if I don't use the 928Intl rebuilt unit. And I'll be curious to see if that has a damper.

Mrmerlin

Bill IMHO, I would suggest to install the Damper, I am sure that 928INTL has used ones,
the last Auto I did had 3 bearings with the damper placed between the center and rear bearing.
Based on a few threads where others have omitted the damper they then were chasing a vibration that the damper would have eliminated

SeanR

As long as the shaft is good Bill, Mark should take it as a core. it's when the shafts snap that he usually refuses them, understandably so. I've used quite a few of his rebuilds and have been very happy with the results.

Bill Ball

Stan:

Thanks for your advice. The problem I see with the used dampers is that the carriers are worn, so the rubber spring element inside the damper no longer works. So, they don't dampen - they just add weight and are a timebomb that will break up like mine did. The rebuilt TTs I have seen, including one in George's car that did not vibrate, had no damper. George's only had 2 bearings and seems to work fine. I do have a used damper coming in. If it sits firm in the tube, I'll use it, and I'll restrain it from moving and wearing the carrier further.

daveo90s4

For what it is worth. My 90 S4 auto: three bearings, no damper, no vibration. I was advised to make sure my middle bearing was not equidistant between the adjacent bearings. The logic, and it sems very plausible to my lay brain, being that by not being equidistant it will prevent sinosaudal (sp) wave forms.

Bill Ball

Thank you, Dave. The unequal postioning makes sense. I will measure the position of the two bearing carriers. Also, I'm not surprised 3 bearings works well for you.

So, I have a rebuilt TT coming . Also, Rob Edwards has a couple of dampers and one has damper carriers that are the correct size to fit my damper and are in reasonable shape. So, that gives me the option of reinstalling the original damper. There are various dampers with different carriers and the carriers are not interchangeable due to various diameters of the damper center bushings. The same problem occurs with the bearing carriers. Ones from 25mm shaft won't work with 28mm. The bearings and bushings are different outer and inner dimensions. So, you can just swap bearing and bushings if the carrier is not the correct one to begin with. One way or another, I should be back in business by next Wednesday.

Rob Edwards

Yeah, per Bill's post, I pulled out the two dampers I've not reinstalled in TT's when rebuilding with Superbearings. One from a 91GT tube looks like the one from Bill's '89 tube.




The other damper I have, I think it came out of Dan Hebert's TT, which was a replacement that Kai installed before Dan bought it, so who knows what its heritage is. It's shorter and the rubber donuts are spongier:



Here are some random bearing carrier dimensions, just for the hell of it:





These carriers are from the 91GT (5-speed..) TT:

Tom. M

I'm pretty sure Kie's torque tube came from Mark at 928Intl because I returned the core from the turquoise car to Mark when I went down to Sharktoberfest that year..

Rob Edwards

Oops, Kie, not Kai, must have been thinking of Kai Ryssdal. By heritage, I meant to say 'year', as the part # on that shorter damper (928 421 601 01) is 'later' than the one out of the '91 TT (928 421 601 00). So either it's a succession part, or was used in automatics, or ???? I do know that it's lighter (7 lbs 3 oz) than the 91GT damper (7 lbs 15oz), maybe the mass difference is 'tuning' for different shaft diameters? From weighing a set of carriers and damper, a trio of Constantine's superbearings are almost identical in weight, not sure whether that's coincidental or not. But it makes me wonder whether there's a pattern to the use of these different dampers.

Apologies for the rampant speculation in this post...

Bill Ball

So, what Rob is sending me that matches my current damper would be the carriers from the damper ending in ME02 in the 1st pic in post 38. The carriers slip over the damper's central bushing which is shown in the 3rd pic as having an inner diameter of 38.28mm.

Rob Edwards

Yep.

GregBBRD

Porsche, the people that made the front fenders and hoods out of aluminum, the intake manifold and valve covers out of aluminum, and the spare tire out of aluminum....all to reduce weight on the 928, didn't put that damper inside the torque tube because they felt a few more pounds, down low, would make the car handle better.

The logic that the "super bearings" negate the need for this damper makes some sense...although one could certainly argue that the damper weight should be located in a specific spot and not "spread" out throughout the entire tube.

Many years ago, when I was but a youngster and was working in the garage at Alpha Beta, I remember that we had sent out one of the "exec's" Lincoln for a transmission rebuild. When it came back, there was a huge vibration....which was chased for an extended period of time. Turns out that there was a large damper than bolted onto the rear of the transmission that had been left off. The "loose" damper was located and re-installed....and the vibration problem was solved.

dcrasta

Not that I disagree with you, however do you believe the damper was installed to reduce vibration for comfort or some other reason? Porsche has a lot of items on this car that are not directly related to performance. This item is not (as far as I know) on the 5 speed cars. I cannot think of a real engineering benefit to having it.

I removed my damper when I rebuilt my torque tube. I have not noticed any additional vibration during normal driving (however in 'normal' driving you rarely get over 3000 rpm's if you drive conservatively). Even cruising at 80mph I'm under 3k and if I'm over 3k I'm not thinking about that vibration.

I feel the damper is another point of failure and I cannot think of a actual benefit of one. The V8 is very smooth when its running correctly and the CV joint condition (in my experience) can contribute more vibration than the lack of damper seems to (on my car).

Any ideas or do you really feel there is an additional benefit of having it?

My TT puking its damper (excuse the cell photo).

Bill Ball

It is.