The Torque Tube Restoration Thread (4200/GS/Spyder)

[FIFTY]

Here are some photos of my Torque Tube being rebuilt by the guys at Augment Automotive.

The rebuild has been broadly a success, I have only had the car back for 2 days and covered 250 miles - I have to keep the revs down and avoid hard accelerations for 500 miles so half way there. So far it feels much smoother between gears with less random vibrations being thrown into the car while shifting or cruising at motorway speeds.

On cold start ups the tube used to make quite unpleasant scraping sounds which have now ceased. There is still a noise coming from the tube which is most audible when in an enclosed space parked stationary in natural... It's basically the sound of the bearings turning, not sure if this can be totally eradicated but it has massively improved from how it sounded before

Pics of the rebuild supplied by Tom at Augment:

 

[FIFTY]

Photos continued

 

[Ebenezer]

For the mechanically ignorant, exactly what did rebuilding entail? There was me thinking the torque tube is a drive a shaft with a jointy thing like you see slung under lorries driving the back wheels...
Eb

 

[FIFTY]

For the mechanically ignorant, exactly what did rebuilding entail? There was me thinking the torque tube is a drive a shaft with a jointy thing like you see slung under lorries driving the back wheels...
Eb

All 4200/GS/Spyder and some GT/QP are a transaxle design with the gearbox at the rear. The bell housing and gearbox are linked with a torque tube - which is a tube with a drive shaft and in this case 4x bearings to hold it in place.

The bearings wear out over time causing loud noises and the shaft to move around inside the tube which causes vibrations and will potentially wear out the bearing on the gearbox.

Augment specialise in Porsche 928s which have a similar transaxle design. They have a special press which can dismantle and then press the tube back together once the rebuild is done. They had to laser cut a special adaptor for their press to work with the 4200 tube and the bearings are a custom design special ordered from SFK, specified to the highest tolerances.

Photos of the tube on the press with the new bearings being installed:

 

[safrane]

Any idea what caused the issue in the first place?

 

[FIFTY]

Any idea what caused the issue in the first place?

The bearings wear out over time/mileage

I noticed that it got noisy at 60k and the tube was restored at 72k miles

Here is the wobble on the old tube, the shaft spun freely, you could hear the noise but I cut the audio as you can hear AV speaking. It was also possibly to physically move the shaft up/down/etc which showed the play in the bearings

New tube... There is maybe a 0.5mm run out on the bearing which I am told is within the tolerance of the bearings - much better than before. The shaft doesn't spin so freely and is held in place.

 

[safrane]

Hmm.... no sign of noise in my old CC at 72k, It seams rather premature at those miles or am I nieve?

 

[FIFTY]

Hmm.... no sign of noise in my old CC at 72k, It seams rather premature at those miles or am I nieve?

They all make a noise. More obvious on manual cars as on CC/F1 cars the actuator holds the clutch off the flywheel for a few minutes in neutral so the TT doesn't spin straight away in N like it does on manual cars

 

[CatmanV2]

For the mechanically ignorant, exactly what did rebuilding entail? There was me thinking the torque tube is a drive a shaft with a jointy thing like you see slung under lorries driving the back wheels...
Eb

Not quite. Thats just a drive shaft with a universal joint in it. A torque tube has a drive shaft inside it (no universal joint) but locks the engine and the gearbox together into a more rigid structure that would be gained by having them bolted to opposite ends of the body shell.
So when you boot it there's power lost in twisting the body and more available for spinning the wheels.
At least that's my understanding.

C

 

[hladun]

Fifty, are those tubular spacers that go between the bearing assemblies shown on the table? Was the problem that a bearing(s) seized or was it that the rubber outer rings dried and failed?

 

[FIFTY]

Fifty, are those tubular spacers that go between the bearing assemblies shown on the table? Was the problem that a bearing(s) seized or was it that the rubber outer rings dried and failed?

Correct. The bearing has a plastic sleeve on both inside and outside of the bearing... These were in surprisingly good condition.

The problem was the 4x bearings developed play and created an oscillating effect. This is a prevailing problem with transaxle designs.

I don't have a video of it but Ed and Aldous at AV Engineering said you could move the shaft by a few mm up/down/etc but with the refreshed bearings it has zero play in it

 

[Oneball]

Blimey the prop/driveshaft itself is dinky-woo isn’t it!?

 

[TimR]

Blimey the prop/driveshaft itself is dinky-woo isn’t it!?

Just a rubber band....!

 

[philw696]

Good work indeed and Great pictures too.

 

[Ebenezer]

So the only difference in practical terms between a drive shaft and a torque tube is where the gear box is. You place the gearbox at the rear for better weight distribution?
Eb

 

[CatmanV2]

So the only difference in practical terms between a drive shaft and a torque tube is where the gear box is. You place the gearbox at the rear for better weight distribution?
Eb

No, sorry. You can have the gearbox at either end. I wasn't clear (although you certainly can place the gearbox at the back for weight distribution purposes.

The practical difference is the torque tube makes a mechanical fixing between the engine / gearbox at the front and the transaxle at the back (in a front engine and gearbox car) or the engine at the front and the gearbox / transaxle at the rear (in a rear gearbox car)

The old transaxle Alfas (116 Giulietta, 75 etc) had a rear gearbox, front engine. No torque tube.

When you boot it the engine spins, the driveshaft spins and tries to turn the gears in the transaxle (or input shaft of the gearbox). That transaxle or box will resist due to inertia, friction all that good stuff.

That twisting motion (torque) has to go somewhere and one of the places it can go is into twisting the engine against its mounts at one end, and the transaxle / gearbox at the other. That takes everything out of alignment and imparts a twist on body.

With a torque tube, that's there to absorb the twisting motion by locking the two units, front and back, to try and keep them in alignment.

Does that help at all?

C

 

[Ebenezer]

Yup - Now I undersatnd what the torque tube is for! Ta
Eb

 

[CatmanV2]

Yup - Now I undersatnd what the torque tube is for! Ta
Eb

I'm gratified on two counts

1. That I have not been corrected (yet)
2. That I seem to have helped

C

 

[oaros]

Many thanks for being the pioneer on this.

 

[FIFTY]

I have done over 500 miles on the new torque tube and seemingly it is working as expected

I noted a noise from the gearbox end of the tube in my first post. The weird noise got louder by the second day of regular use. It went away with the clutch pedal pressed down and then came back with the clutch pedal back up again so clearly a problem toward the rear of the car where the noise was the loudest.

I took the car to my specialist this morning and had it up on the lift, did the same thing with the clutch and the noise is very clearly coming from inside the gearbox (yikes). So I had very little option but to leave it with Voicey and Ed for a gearbox rebuild.

The theory is that the bearing on the input shaft of the gearbox has got excessively worn due to the run out on the drive shaft caused by the play in the bearings. With the new TT fitted which is turning true compared to how it was before it has exposed the worn gearbox input shaft bearing. The car drives fine but it has this worn bearing sound, the risk is that the bearing fails and lunches the gearbox with the potential to take the diff and TT with it.

To others I would suggest that at the very minimum to check the wear in the Torque Tube bearings and check for run out at the gearbox end of the shaft at every clutch change... if you have play in it then take it to these guys for a rebuild or it will eventually lunch the gearbox.

I have attached a photo of what the input shaft and bearing looks like on a F360 gearbox that was being rebuilt there. It's the same box in the 4200.