Diff bush - Powerflex pollybush or Z3?

Sun Jun 12, 2011 10:04 pm

Need to buy new diff bush tomorrow. Question is should I go for pollybush type or Z3 solid rubber bush?? Which is better?

Mon Jun 13, 2011 12:39 am

I have used both and cannot tell the difference.

Polybush will fit with no hassle,Z3M bush will need the back plate off at least,if not the use of a press.

Mon Jun 13, 2011 6:10 pm

Z3 bush is made for 300bhp and has some give in it. Or you can buy rock hard cheap crap and liken the chance of pulling the whole lot off the boot floor. That bracket is only held on my a few spot welds!

Maybe a concrete one?

Tue Jun 14, 2011 6:23 pm

z3m bush gets my vote every time!! The powerflex one is crap imo.

Tue Jun 14, 2011 7:12 pm

+1 iv a power flex one and its crap, only have a 316i and it doesnt sit right anymore.

Never getting it again

Tue Jun 14, 2011 7:19 pm

penton08 wrote:z3m bush gets my vote every time!! The powerflex one is crap imo.

This

Tue Jun 14, 2011 11:21 pm

I fitted a Powerflex one originally and it shifted out of place twice.

So dumped it and went for a Z3 one. Much better in my opinion.

Wed Jun 15, 2011 1:46 pm

Thanks for advice - will send powerflex bush back.
Just ordered Z3M bush

Wed Jun 15, 2011 1:59 pm

Not only are the polyflex ones hard and transmit noise, they ruin the handling. The Std BMW bushes are edsigned to deform, and have a hysteresis loss angle to aid suspension. The Poly ones don't. The rear beam in E30's is a live suspension component and shouldn't be over-constrained or have the wrong material applied. Don't beleive me? Get a video camera under there and go for a drive.

Passive rear wheel steering and damping are both components of the rubber rear suspension components. BMW (and all other car manufacturers) COULD use polyeurathane if it was a better choice. In volume it would probably be cheaper to make than rubber. They dont.

I personally have a Z3M bush in mine, and E30 rubber beam bushes. I wouldn't be offended as much by poly trailing arm bushes but even they aren't as good as rubber. They introduce friction, where a rubber bush constrained around the perimeter and centre acts as close to zero friction as you can get.

I'm really not an advocate of poly bushes any-more. On certain parts of the suspension they can have their place: ARB droplink mounts and possibly even the TCA rear bushes, but not the rear beam.

Regards,

Jai

Sat Jun 18, 2011 12:29 pm

Took rear diff plate off to have new Z3M bush pressed in... I now have a back plate with a smart Z3M bush in it - including a nice big crack running through back plate... Wishing I had gone the polly bush route now, what a start to a sat morning..., pissed off

Sat Jun 18, 2011 12:32 pm

mattqf77 wrote:Took rear diff plate off to have new Z3M bush pressed in... I now have a back plate with a smart Z3M bush in it - including a nice big crack running through back plate... Wishing I had gone the polly bush route now, what a start to a sat morning..., pissed off

Oh dear!

I presume that this is a medium case diff back plate?

I have a small case back plate in my stash,of course.....

Sat Jun 18, 2011 12:37 pm

Yes, medium case.. Does any one have a spare medium case diff back plate they want to sell me?? in London area. Planned to fit it today and get car back on the road..

Sat Jun 18, 2011 12:39 pm

mattqf77 wrote:Yes, medium case.. Does any one have a spare medium case diff back plate they want to sell me?? in London area. Planned to fit it today and get car back on the road..

Shove this in the 'Parts Wanted',some-one,some-where,will have one!