Split Torque Tube Rebuild

[Bergerac]

Its generally said the split torque tubes in S2's and 968 aren't rebuildable due to the first bearing not staying in place. Since I've not been able to source a solid torque tube for my car we're attempting to modify ours to solve this issue.

Torque tube out the car ready to remove the driveshaft and old bearings. The split had widened from just under 3mm at the ends to nearly 6mm in the middle. I wont go into detail of stripping the tube here, we used the technique in the following Youtube video

PXL_20241104_033810091 (1).jpg (3.24 MiB) Viewed 5731 times

Bearings and drive shaft removed, we had an issue with the first bearing going out of alignment and binding up on the driveshaft as we hammered it out. We had to clamp the torque tube to capture the bearing in alignment again and allow the driveshaft to move through easily.

PXL_20241104_050002275.jpg (2.33 MiB) Viewed 5731 times

Once stripped we sent the tube off to be sandblasted, we then marked up the bearing locations ( Were using the Blacksea R&D bearings which are approx 80mm long, you would need to use a different strategy to bracing for the stock sized bearings.) We used some heavy duty tillet hose camps to close up the split while keeping the tube in shape. We measured the split and OD of the tube at 100mm intervals to ensure it was consistent along the split and solid sections.

PXL_20241111_052957653.jpg (2.16 MiB) Viewed 5731 times

We had our fabricator weld on some gussets either side of the bearing locations for bearing one (middle of split) and bearing two ( end of split). He turned up a small plug to insert into the tube while he welded it to prevent any distortion.

PXL_20241116_060453389.jpg (2.02 MiB) Viewed 5731 times

We are waiting for a coat of paint on the TT and driveshaft to dry and will be rebuilding the TT later this week, Ill share some more photos once its complete.

[Tom]

Its generally said the split torque tubes in S2's and 968 aren't rebuildable due to the first bearing not staying in place. Since I've not been able to source a solid torque tube for my car we're attempting to modify ours to solve this issue.

Torque tube out the car ready to remove the driveshaft and old bearings. The split had widened from just under 3mm at the ends to nearly 6mm in the middle. I wont go into detail of stripping the tube here, we used the technique in the following Youtube video

PXL_20241104_033810091 (1).jpg

Bearings and drive shaft removed, we had an issue with the first bearing going out of alignment and binding up on the driveshaft as we hammered it out. We had to clamp the torque tube to capture the bearing in alignment again and allow the driveshaft to move through easily.

PXL_20241104_050002275.jpg

Once stripped we sent the tube off to be sandblasted, we then marked up the bearing locations ( Were using the Blacksea R&D bearings which are approx 80mm long, you would need to use a different strategy to bracing for the stock sized bearings.) We used some heavy duty tillet hose camps to close up the split while keeping the tube in shape. We measured the split and OD of the tube at 100mm intervals to ensure it was consistent along the split and solid sections.

PXL_20241111_052957653.jpg

We had our fabricator weld on some gussets either side of the bearing locations for bearing one (middle of split) and bearing two ( end of split). He turned up a small plug to insert into the tube while he welded it to prevent any distortion.
PXL_20241116_060453389.jpg

We are waiting for a coat of paint on the TT and driveshaft to dry and will be rebuilding the TT later this week, Ill share some more photos once its complete.

Very interesting stuff, looking forward to hearing how it turns out, I wasn't aware the S2 and 968 TT's had that slit in it. What's the purpose of it?

[Thom]

Don't quote me on this but I believe the slit was an attempt to cut down vibrations supposedly caused by the larger engines.

[dr bob]

Don't know if this adds any value to the discussion --

For the not-split torque tube in my 928, I added a couple pop-rivets through the tube at each bearing to keep them in place. The front one particularly likes to walk forward toward the bellhousing, a challenge that can't be solved with an ABS sleeve between bearings inside the tube. Pop-rivets are handy in that you can easily drill them out next time the bearings actually need to come out. This may not be a concern or even desirable with the Black Sea bearings in the rubber carriers, but for the original-style bearings it works a treat.

Challenges with the solid tube have included spiral stress cracking from vibration/resonance under high loads. Perhaps the split tube is to eliminate that resonance?

Watching.

[Bergerac]

Yes I believe it was a vibration/resonance mitigation measure for the 3L motors. The dual mass flywheel in the 968 solves this issue.

Constantine from Blacksea attempted to use rivets to pin the first bearing from what I understand but it still lead to the first bearing moving.

I wish I had gotten better photos of how distorted the tube was, I can only imagine how much it was moving under dynamic load and hope the bracing I've added holds up to that stress

[Zirconocene]

I've wondered for a long time why I'd never seen anyone take the approach you did to fixing the split TT. It's hard to know why that wouldn't work.

Following up on @dr bob 's comment, it seems to me that drilling and tapping a hole for a stout, short bolt, would also work well, perhaps something like an M10 x 20 mm. These things don't have to be rebuilt so often, I guess, that that level of ability to disassembly would be required but I like to think long term about my cars, I guess.

Cheers

[Bergerac]

Its been

I've wondered for a long time why I'd never seen anyone take the approach you did to fixing the split TT. It's hard to know why that wouldn't work.

Following up on @dr bob 's comment, it seems to me that drilling and tapping a hole for a stout, short bolt, would also work well, perhaps something like an M10 x 20 mm. These things don't have to be rebuilt so often, I guess, that that level of ability to disassembly would be required but I like to think long term about my cars, I guess.

Cheers

Theres a few people who had done it in the past.I am a little concerned since I will be pushing into the high 400s that the TT will twist and pop those welds, well see I guess.

[MXK944]

From the classic training manual

Transaxle

The central tube is slotted at the front to avoid torsional resonances which are transferred from the engine to the transmission via the central tube. The slot is sealed with adhesive film to protect against the ingress of dirt.

[cda951]

Hi @Bergerac ,

Any updates on your progress? I am now faced with the prospect of attempting to rebuild my 944S2 cabriolet split torque tube or attempting to locate a good solid version and hope the vibrations aren't too bad. This car is a super smooth cruiser with zero pretensions for performance use, I have a modified 951 for that purpose.

Thank you!

[Bergerac]

Its finished but it hasnt gone back into the car yet. The front bearing is definitely more secure though.

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