[Beeza]

The car has now been reassembled after repairing the broken bolt that secures the forward sliding shaft that engages the clutch. A new clutch plate has also been installed as the old one was shot.

We are now experiencing a new problem. At exactly 2800RPM the car vibrates and a loud metallic clatter can be heard from inside the torque tube. With the clutch depressed the vibration ceases and the engine runs smoothly. At all other RPMs it sounds fine. it only happens at 2800RPM and with the clutch engaged. Could the torque shaft be out of balance? Can they be re-balanced? What about the bearings inside the torque tube? How many are there? Can they be replaced?

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[flash]

i believe there are 2 bearings - they can be replaced - it requires a long ram press to do the job

what flywheel is in the car?

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[Beeza]

It has the original dual mass one.

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[flash]

hmmm - i'm wondering if you have a different problem - the torque tube bearings should make the noise and vibrate pretty much across the board of revs, and not just at one point

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[Monstrous4Banger]

I think some have 3 bearings. There is even an upgrade now. Pain in the butt to do. Sounds like thats most likely it, if its definitely coming from the torque tube.

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[flash]

it's so hard to track down noises in this car - i spent $6500 chasing down a rattle in the transaxle, which included replacing torque tube bearings, and rebuilding the transaxle twice, and it turned out to be caused by the aluminum single mass flywheel and nothing could be done about it

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[PorscheDude]

It's possible the DMF is on it's way out. The rubber inside deteriorates inside affecting harmonics.

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[Monstrous4Banger]

Ya, theyre real tricky to diagnose. Sounds in that area seem to echo all around. Normally it does it in all RPMs. If its definitely coming from the middle of the car, its the bearings. Make sure you pinpoint where its coming from. When mine went out I luckily had a spare.

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[blue968]

I Had the same problem you are describing and I had thought it was the dual mass flywheel and it turned to be the torque tube. It would only vibrate in a certain RPM, cant remember what it was but I want to say around 2500 and would not go away from that point all the way up. Was fine below 2500, and could really feel it the center by the shifter. I remember sliding my hand down the side of the passenger seat and you could really feel it down there. I bought a used torque tube for about 400 give or take a bit.

Good luck

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[RS Barn]

All of the Torque tube bearing failures I've seen happen above 4K and get violent.
If any of the bearings fail, the TT occilates wildy .
Usually the head on the Allen bolt on the intermediate shaft going into the clutch disc have a corner worn off. The TT moves over an inch when a bearing is bad
A 2800 rpm vibration is usually a balance shaft issue-There are several varaiations.
Pete

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[Beeza]

My initial thoughts were balance shafts. When I bought the car it was vibrating quite badly and my suspicions were confirmed once I had remove the belt covers. The timing belt was broken. I have replaced both belts and the engine now runs sweet throughout the whole rev range with the clutch pedal depressed. No vibration at all.

The vibration only comes on when I let out the clutch and rev it. So I think that would eliminate the engine, balance shafts, flywheel or clutch plate. I have yet to take it on the road as it is still on jacks. I'm waiting for the wheels to come back from the paint shop. Although I have taken it throughout the rev range in all gears whilst up on sticks. The vibration is gradually going away, but it is still there and most noticeable at 2800RPM.

This is the only mechanical job left outstanding after the restoration project before it goes to paint. I'm dreading the thought of removing that torque tube again. That gearbox is a damn heavy piece of kit!

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[flash]

how was the pilot bearing when you had the clutch out?

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[Beeza]

That's a good point. And to be honest I didn't check it. Does it sound like a symptom of it? I didn't remove the flywheel when I changed the clutch. Do you have to do so to check the pilot bearing?

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[Monstrous4Banger]

Pilot bearing usually makes whirring sound, almost like the drone from a jet. It only makes the sound when your moving tho, IIRC.

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[Beeza]

Here's another thought.

Does it matter where you align the front and rear sliding shafts? They were both removed when I had to fix the sheared bolt in the front input sliding tube as I had to drop the gearbox. If the bolt at the front didn't align with the either of the four bolts at the gearbox input shaft, could that set up a dynamic imbalance?

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[RS Barn]

Does it matter where you align the front and rear sliding shafts? They were both removed when I had to fix the sheared bolt in the front input sliding tube as I had to drop the gearbox. If the bolt at the front didn't align with the either of the four bolts at the gearbox input shaft, could that set up a dynamic imbalance?
[/quote]

That is a possibility.
We had n S-2 with 968 gearbox that had a severe driveline vibration-but different than TT bearing.
There were only two bolts in gearbox input shaft and they were on same side vs offset. We put in all four with bolt heads on opposite side and vibration was gone

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