Torque tube bearing inspection

Somewhere on Rennlist there is a long thread on the use of C4 bearings. I think it was a combination of heat build up in between the bearing carriers with no way to escape, and Porsche over-engineering.

watsondk wrote:Good find on actualy C4 bearings.

Not entirely sure why they used C4's from the factory, I can't imagine temperatures being that extreme in the TT, and while the bearings are in there tight a lot of that is due to the rubber insert's friction. I'm guesing the heat from the catalytic converter and exhaust? Any ideas of typical temperatures of the TT?

So as I pulled out my torque tube bearings a few weeks ago I had an "incident". The outer bearing carriers got scraped. I'm sure I'm not the only one this has happened to (like the first post of this thread).

Would anyone be interested in buying some newly designed and made carriers?

Basically I will be reusing the outer rubber to insure the carriers don't "walk" inside the TT but replacing the metal shell with delrin. I will post pictures of the final product and let everyone know if they work when they are complete.

I will have enough material to make several extra carriers if they are successful. For now I will only make enough for myself, however if others are interested I could have the machine shop use the rest of the material I purchased and sell at cost.

I will also have extra material for the inner inserts, although I believe those are available from other sources unlike the carriers.

Guess you are re-inventing Constantine's wheel.........It's a joke..

Only to the extent needed to do the job properly. His setup is truly above and beyond oem, I am simply trying to replace unavailable parts at a reasonable cost.

watsondk wrote:Only to the extent needed to do the job properly. His setup is truly above and beyond oem, I am simply trying to replace unavailable parts at a reasonable cost.

Seems like a reasonable idea.

I am a cheap SOB, so I am interested dependant upon price.

I pick them up tomorrow after work but already have pictures. I will try to upload them tonight. I plan on installing them Friday (4 day week!!!). Will update with how well they install and again with how they work once the car is back on the street.

I will ask the machinist if he would be willing to make more sets and at what price.

Here are the pieces, picking them up from the machine shop tomorrow:

The inner pieces are the basic design from clarks-garage.
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The outer pieces are the important ones, if you have messed up bearing carriers and don't want to buy a new TT assembly these might be for you (if they actually work, which I will find out soon). The bearings are press fit tightly into the delrin. As things heat up the metal has a higher coefficient of expansion and the press fit will become tighter. This design reuses the rubber ring from the bearing carriers. If your rubber pieces are scrapped as well these could be made to work with o-rings with a design change.

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Very interested in the results.

Those things look effing awesome. I hope they work!

Spent some time with the parts this weekend. The machinist didn't exactly do a steller job and I ended up getting a partial refund from him. Of the 8 bushings he made 2 of them met the specs on the drawings I provided...

The two parts that were correct worked great, the other six...well not so much

The main issue is that I specified an interference press fit and the bearings ended up loose in the bushings. He was up to .015" off specified dimensions on some of the ID and OD's which is horrible for a material as easy to machine as delrin. I have been adding epoxy and sanding to get the correct dimensions for the assembly, new plan is to have them installed this next weekend.

I will update after they are in.

What epoxy did you find that adheres to delrin?

I roughed up the delrin with some 60 grit paper and used some "5-minute" 2 part epoxy. I test fit the assemlblies to the driveshaft outside of the TT. I adjusted them until they installed with about the same effort as the stock metal/rubber insert. Didn't have any issues with the epoxy seperating when inserting driveshaft. Time will tell though.

You might want to look for a tube from a car newer than '86 because the pucks are designed better. The rubber "belt" is bonded to the bearing carrier and the bearings press in rather than the carrier being two piece with the bearing sandwiched in between.

Funny, I just did mine this weekend and my G31 tube (1980) had bonded rubber and pressed in bearings and the 1983 944 tube was the same.

Should be C4 clearance, not C3. All of the TT that I rebuilt and/or gutted had "C4" on the outer bearing surface. YMMV

Both of mine had bearings that just say FAG 6006 with no clearance designation which means that they are C2-C3. (normal clearance) I used C3 which are tighter than C4. The ones I used are rated for 8000 RPM and rated for 250 deg C.

I am guessing the lack of a followup means that these instantly melted and dripped out the back of the torque tube... Please prove me wrong!

The parts were actually succesful, just way too much effort.

This past weekend I completed an 850 mile road trip with some very spirited driving without issues from the TT bearings...I did have the FL tire blowout on me but thats unrelated.

To recap I had custom delrin bearing carriers machined to accept the rubber surrounds from the stock pieces. The bearings were then supposed to press fit into the delrin carriers. The machinist did a pretty dismal job so I ended up using a two-part epoxy to secure the bearings into the carriers.

I then pressed the smaller delrin inserts into the bearings. These were supposed to be a tight fit aroud the driveshaft...again the machinist let me down, they were way out of spec. I initially attempted to use epoxy for that as well. The epoxy proved too brittle, cylinder head RTV worked very well though.

When inserting the carriers into the TT I soaped them up to get them in easier. My first attempt was without soap and the rubber surround attempted to come off the carrier.

The only noise now is some clutch chatter and a slightly undersized/worn driveshaft nub.

If I were to do it again I would probably find a used TT and pull good carriers/inserts from it.

Or go to the expert.....