Hey guys, I figured I'd run my problem and potential solution by you.
Last year a did a full underside restoration on my Z4M. If you're interested here is the picture album: https://www.facebook.com/media/set/?set=a.637453398797294&type=3 (I think that's the correct link)
Since then I've done 1000 miles and had no problems EXCEPT the rear axle is loud now. I don't remember hearing it prior to the refurb.
As you driving along at 30-50mph, on low throttle, you can hear a grumbling from the rear.
In terms of causation I very much doubt there is a mechanical problem. I've not had a workshop for over a year so I havn't been able to check it over properly yet, but when new workshop is complete I obviously plan to check all of the rotational parts properly, but I'd be amazed if there was a problem.
Instead I strongly suspect the problem is that I changed the main four rubber subframe bushes for hard aftermarket poly bushes. I've done this on lots of cars before and never had this problem.
My suspiscion is that the hard poly has removed any acoustic deadening from the rear axle and is piping vibration directly into the chassis. In the cockpit it sounds just like listening to a rear axle through a mechanic's stethoscope.
Has anyone else had this problem with rear poly bushes?
Anyway, here is my proposal:
- the proper solution would be to remove rear axle fully and re-fit the proper OE rubber bushes. But rear axle removal on these cars is a nightmare and there's no way I can give it that kind of time at the moment with current job and family.
- instead I'm thinking of dropping the rear subframe down by just 10mm or so. I'll then slip rings of about 5mm of soft rubber between the tops of the bushes and the chassis, then re-tighten. This should remove some vibration from transferring. It won't remove all noise as the big four main bolts will still be transferring vibration directly to chassis. But better than nothing.
- in addition I plan to get 2 fairly hefty blocks of hard rubber and essentially bolt them somewhere to the left and right of the subframe. In my mind these will act as vibration dampeners and remove a bit more noise.
Any thoughts on this please?
Last year a did a full underside restoration on my Z4M. If you're interested here is the picture album: https://www.facebook.com/media/set/?set=a.637453398797294&type=3 (I think that's the correct link)
Since then I've done 1000 miles and had no problems EXCEPT the rear axle is loud now. I don't remember hearing it prior to the refurb.
As you driving along at 30-50mph, on low throttle, you can hear a grumbling from the rear.
In terms of causation I very much doubt there is a mechanical problem. I've not had a workshop for over a year so I havn't been able to check it over properly yet, but when new workshop is complete I obviously plan to check all of the rotational parts properly, but I'd be amazed if there was a problem.
Instead I strongly suspect the problem is that I changed the main four rubber subframe bushes for hard aftermarket poly bushes. I've done this on lots of cars before and never had this problem.
My suspiscion is that the hard poly has removed any acoustic deadening from the rear axle and is piping vibration directly into the chassis. In the cockpit it sounds just like listening to a rear axle through a mechanic's stethoscope.
Has anyone else had this problem with rear poly bushes?
Anyway, here is my proposal:
- the proper solution would be to remove rear axle fully and re-fit the proper OE rubber bushes. But rear axle removal on these cars is a nightmare and there's no way I can give it that kind of time at the moment with current job and family.
- instead I'm thinking of dropping the rear subframe down by just 10mm or so. I'll then slip rings of about 5mm of soft rubber between the tops of the bushes and the chassis, then re-tighten. This should remove some vibration from transferring. It won't remove all noise as the big four main bolts will still be transferring vibration directly to chassis. But better than nothing.
- in addition I plan to get 2 fairly hefty blocks of hard rubber and essentially bolt them somewhere to the left and right of the subframe. In my mind these will act as vibration dampeners and remove a bit more noise.
Any thoughts on this please?
