New polybushes - car now vibrating at speed

J

James Junior

Member
 Manchester
Just had powerflex bushes fitted to the front wishbones on my Z4 Coupe as the old bushes were knackered and sending a lot of feedback through the steering wheel at around 30mph.

This now appears cured, but now getting bad vibration through the whole car at speeds of between 40 and 90 leptons instead.

I had hunter wheel alignment done earlier this year before sorting the bushes. Might I need this doing again do you think?

Any pointers would be gratefully received. :-)

Car wears staggered 19" CSL reps by the way if of any consequence.
 
Get the alignment checked defo.
With the poly's and 19's it will be super sensitive to alignment issues
Assuming that your wheels and tyres are correctly balanced. (may have lost a balance weight?)
Check tyre tread wear across the width and look for unusual tyre wear also. GL. let us know what it was when you find out :thumbsup:
 
I don't want to be the bearer of harsh news (no pun intended headmaster) but the changing of one suspension component from standard is in danger of setting up unwanted vibration. The system including tyres is carefully designed to avoid harmonic vibrations, the bushes you removed were probably a composite with inbuilt damping which is now absent. OEM bushes cost far more than polybushes and if BMW could get away with them they would. I used to fit them to club rally cars years ago because they suited the purpose but wouldn't fit them for road use as they also impose stress on other components.

Cure? as above systematically eliminate every source of vibration, wheels balanced on the car will help eliminate whole unit imbalances including brakes, 4 wheel alignment, rotational alignment on the car (for wobble), a thorough examination of all suspension components/links/bushes may throw up something. Cheap or damaged wheels can do it, but my guess is tyre tread imperfections mentioned by Toe-side such as minor bulges or worn areas may be the cause. I had a problem with brand new tyres which had a fault in the carcase structure which could only be detected by running a hand around the wheel and measuring off the car, so check carefully.

However it can just be down to road surface resonance with your unique combo of wheel/tyre/suspension/wear which cannot be fully eliminated, some forum members have ended up removing poly's. I hope you get it sorted, Good luck
 
Thanks for taking the time to post such a detailed response. Hmmmm, that's a bit worrying.

Had only ever heard good things about Powerflex bushes previously.

Either some balancing and alignment shenanigans will sort it out, or I've gone on a rather costly wild goose chase.

Ah well, easy come easy go, have booked the car in for an inspection with the BM specialist who fitted the bushes so will see what they say.

If we've got to rip them out and stick some OEM bad boys in there it's not the end of the world...

Keep your fingers crossed for me fellas!
 
Just wanted to say thanks again for your input chaps.

BMTec got their hands on the car this week and found the wheel balancing was way out. Half an hours labour to recalibrate and the car is perfect. All vibrations gone and she now handles better than anything I've ever owned.

Good times.
 
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