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Discussion Starter #1 (Edited)
Okay, after a full restore my propshaft is vibrating badly at idle. I marked up where the front and rear join so as to connect them back after fitting new donuts and centre support but as you can see from the video there is way too much movement.

any help/suggestions greatly appreciated.


Thanks
Chris
 

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At least some of the vibration you see is from the engine moving around at idle, not a drive shaft misalignment, as you can see from the movement of the down pipes and exhaust flex sections. Try engaging the starter with the sparkplugs out to turn the engine over without ignition vibration to see if there is actual driveline misalignment.
 

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You didn't bend the driveshaft to remove or replace did you?

When you install a driveshaft you are supposed to leave the pinch bolt loose, start the engine, rev it up a few times and let the driveshaft shift itself to find a position with no built in stress involved. Then, (after stopping the engine...!) snug up the pinch bolt.

See: Alfa Romeo Driveshaft Troubleshooting
 

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Discussion Starter #4
You didn't bend the driveshaft to remove or replace did you?

When you install a driveshaft you are supposed to leave the pinch bolt loose, start the engine, rev it up a few times and let the driveshaft shift itself to find a position with no built in stress involved. Then, (after stopping the engine...!) snug up the pinch bolt.

See: Alfa Romeo Driveshaft Troubleshooting
Excellent link thanks, I don't suppose there is any way to shorten the snubber without dropping the gearbox? again!!!



Thanks

Chris
 

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Was the vibration present before the flex discs were replaced? If not, it's quite possible that there was an assembly error that I have seen before.

Where the two halves of the propshaft mate to one another, & again where the rear flex disc attaches to the propshaft, there is a metal bushing that sits on a ball end of sorts in such as way as to allow the bushing to pivot about the ball end. Each of those bushings needs to sit perfectly centered in its corresponding hole; one on the opposite half of the propshaft, the other contained in the rear flex disc.

These two places are where a common assembly error occurs. The fit between each bushing & its corresponding hole is fairly precise. Because of that & because the bushing is free to pivot on its ball end, it is difficult to get the bushing to slide straight into its hole while remaining loose & centered on the ball end.

As the parts are assembled, the tendency is for the bushing to either get ****ed to one side or to be pushed straight back in such a manner that it seizes against its ball end. It is possible to force things together in this manner. If that happens, you will have a propshaft vibration. I learned from someone more experienced that this is a common mistake.

I saw this in another car that had a propshaft vibration that I could not diagnose. Thinking that it was inbalanced or bent, I removed it in order to send it to a shop in CA who claimed that they could repair these propshafts (Unfortunately, the name of the shop escapes me). With the propshaft out of the car, I removed the rear flex disc to find that this bushing at the end of the propshaft was seized against its ball end. Some delicate taps with a brass punch freed it. After proper reassembly, & after checking the bushing at the center of the propshaft, the vibration was gone.

If the basics don't check out, & you're faced with removing the propshaft again, check those little bushings before concluding the worst.
 

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Discussion Starter #6
Was the vibration present before the flex discs were replaced? If not, it's quite possible that there was an assembly error that I have seen before.

Where the two halves of the propshaft mate to one another, & again where the rear flex disc attaches to the propshaft, there is a metal bushing that sits on a ball end of sorts in such as way as to allow the bushing to pivot about the ball end. Each of those bushings needs to sit perfectly centered in its corresponding hole; one on the opposite half of the propshaft, the other contained in the rear flex disc.

These two places are where a common assembly error occurs. The fit between each bushing & its corresponding hole is fairly precise. Because of that & because the bushing is free to pivot on its ball end, it is difficult to get the bushing to slide straight into its hole while remaining loose & centered on the ball end.

As the parts are assembled, the tendency is for the bushing to either get ****ed to one side or to be pushed straight back in such a manner that it seizes against its ball end. It is possible to force things together in this manner. If that happens, you will have a propshaft vibration. I learned from someone more experienced that this is a common mistake.

I saw this in another car that had a propshaft vibration that I could not diagnose. Thinking that it was inbalanced or bent, I removed it in order to send it to a shop in CA who claimed that they could repair these propshafts (Unfortunately, the name of the shop escapes me). With the propshaft out of the car, I removed the rear flex disc to find that this bushing at the end of the propshaft was seized against its ball end. Some delicate taps with a brass punch freed it. After proper reassembly, & after checking the bushing at the center of the propshaft, the vibration was gone.

If the basics don't check out, & you're faced with removing the propshaft again, check those little bushings before concluding the worst.
thanks for the detailed reply.
The engine was running extremely poorly when I got the car, so was unable to drive and so do not know if the problem existed previously.

Yes the propshaft was mated and in one piece.

It looks like the problem is on apparent with at very low revs >1000 it may be linked to the engine itself vibrating at those low rpms.

thanks
Chris
 

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While that's possible, don't rule out a propshaft problem. If you rev the motor slightly while sitting in the car, a propshaft vibration should be felt in the seat of the pants more than an engine vibration. I'm working on a GTV6 right now that was running rough due to low compression in #6 (bent intake valve). When I drove it, there was no propshaft vibration despite the engine vibration.
 

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Are you sure that it is the propshaft and not bad motor mounts?
 
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