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Rear Vibrations.

S

SECTOR

PCGB Member
Member
Hi all, any ideas about the following:

993 C4 MO30 suspension with H/D bilstiens.
New rear discs fitted.
Suspension / bushes / wheel allignment checked by Centre Gravity - all ok.
Wheel balancing checked etc etc.
The car always seems to have a slight vibration at speed from the rear at speeds of 80mph +. There is a strange vibration that occurs from time to time. Suddenly whilst, say pulling away from an traffic island or similar, the rear of the car starts to vibrate ( when it first did it I thought I had a flat tyre).As you accelerate it stays with you, through the gear changes etc. If you coast or dump the clutch it is still present . It will not go away until you bring the car to a holt, engine running still, pull away and then its fine again for a few days or anything up to 200miles ish.
It is almost like something has been thrown out of balance and once it starts it wont stop until the rotation is stopped. Then it is fine again.
Has anyone experianced this.
I am having the drive shafts checked and the engine mounts checked as I believe these are oil filled and can loose there pressure.
Regards
Stephen

 
Thank you for you reply. When the harsh vibration occurs this comes in from low speed and does not vanish until the car is brought to a halt. You then you set off again, and the vibration has gone. I also somtimes feel a slight vibration at 80mph +. They are both speed sensitive.
I think this is to hard to describe on here. I was hoping somebody might have experianced the same problem, to save me replacing bits such as engine mounts / drive shafts etc for no reason. The person who is dealing with the problem is unsure himself. He is a porsche specialist.
Thanks once again.
 
This won't be much help, but I'd be careful you don't get thrown off the sent by thinking both symptoms are the same fault. The 80+ problem might be a completely different issue from the slow speed one.

Did either of them start when you had the rear disks done? (or is you list of recent fixes all to try to fix the problem?)
 
Thanks for the reply. I needed new discs anyway, but the problem was there before.
I was out in the car last night and it drove perfectly. Wish it would just vibrate and not stop, then we would find it.
Cheers
Stephen
 
Stephen,

Have you very carefully checked the rear tyres for bulges or distortions? I know you have had them balanced, however, they tyre is not under load on the balancing machine and can behave quite differently on the car. Also, when the tyre has warmed up the rubber softens and flexes differently.

Taj
 
Had a similar problem last year. Had new discs&pads some time prior, so pads were fairly fresh at that point. Motorway cruising, conditions damp. Vibration would start after 1 hour, felt like a puncture. Checked on the hard shoulder, tyres fine, felt around each tyre to check for nails, etc. nothing. Started off, and the problem had gone.

Happened three times on different occasions (same route), the independent though it could be the pads rubbing, so they filed them down a bit Problem solved....... (never happened since anyway)

 
Does sound like the rear discs/calipers because, unless it's a coincidence, those bits that have been changed could be the most suspect and you presumably didn't experience it before. I reckon you should get the people who did them to have an extensive check of them and anything in the area[;)]. For instance, are the rear wheel bearings OK? These can have a strange "˜now you hear it, now you don't' effect too.
 
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