Powerflex bush -Correct ?

Spriteracer

Spriteracer

Member
 West Wales
Morning all. I was carrying on with the rebuild of the rear end over the weekend, replacing bushes etc. Question I have is re. the top arm outer bush. According to Real oem and as I found on the car, this is a ball type bush with some movement. The Powerflex substitute is a straight fixed bush. Is this correct ? and if so could any one who has already done this say if there is any significant difference in use. Thanks.

Also - When changing the RTABs I found some corrosion in the bracket socket - same both sides. I have cleaned it up and applied copious amounts of rust converter to slow it down but it seems to be an area where serious damage could occur without being noticed. ? worth keeping an eye on ?
 

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Not a problem - all and any help and advice gratefully received !

Re the other part of my original post on the top arm outer bush, I have come to the conclusion that BMW must have specified it as moveable while the bottom arm outer is a fixed bush for a reason - so have decided to replace like for like. I'd be interested if anyone knows why the difference, but maybe to do with the toe adjustability ?
 
The Z4M has balljoints top and bottom.

I speculate, but might be for NVH reasons that the non-M cars have a rubber bottom bush.
 
If you mean the rearm arm outer upper / lower bushes - then no I wouldn't use Powerflex there.

I would - and did - https://www.pistonheads.com/gassing/topic.asp?h=0&f=47&t=1755842&i=63 - upgrade to the ball joint ones.

I like Powerflex's stuff but some of it seems objectively worse than the OE stuff.
 
Thank you both - Liam and Jakg. I have already fitted the Powerflex lower bushes, and so will see how it feels. They are at least the simplest to change back to ball joints if the PF doesn't work. On a quick look at Real OEM the other differences between Si and M seems to be the trailing arms and the rear axle carrier (subframe) which have different numbers. Pictures seem to be the same so no idea what is the difference in practice and if the bottom joints are affected by that. Assuming also that the pick up points on the shell are the same. BMW chassis engineers are very bright people but it does seem odd to have two different types of movement in that location and I suspect Liam is right on NVH / cost reason. I can cope with cart springs and lever arms but Zs have far too many arms for my poor brain to get around.

Just to add I have the greatest respect for all those who do all this on axle stands ! I'm very fortunate to have a pit in the garage which makes life so much easier.
 
A question for Liam if I may ?

Re the "M" rear hub carrier bottom ball joint mentioned above - did you change your standard fixed bush for the M ball joint type and if you did, did you notice any appreciable difference before and after ? If it is worth it I might as well do this while awaiting the drive shafts back from the specialist.

Many thanks.
 
Yes I did.

But I replaced every component of a tired suspension system in one go. So I don't have a valid before/after comparison.
 
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