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Rear Frame Bushing Removal Sucess.......

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Brucey
6 Series Guru
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Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Rear Frame Bushing Removal Sucess.......

Post by Brucey » Tue Mar 27, 2018 9:40 pm

IIRC the tyres didn't wear terribly oddly on the burgundy car but I always thought the steering felt slightly odd. Having spent half a day making adjustments to the steering box on that car it was clear that you could make a big difference that way but it still felt slightly different to most other 6ers I have driven. It could have been one of a number of things but the prediction is that with the upper control arm bushes offset differently the car will suffer some bump steer.

In corners the car rolls and the suspension extends one side and compresses the other. This ought to produce a different steering response if there is bump steer. However this is complicated by the fact that the UCA bushes see a lateral load too; The outside one soon hits a hard/firm stop (in the stock bushes and the E32 type) and the inner one extends easily (but there is usually less load on it anyway). WIth stiffer bushes this happens less. Presumably the stock geometry is worked out so that the standard bushes move in such a way as this results in little net bump steer.

There are three main possibilities for the UCA bushes

- stock (offset centres)
- Modified (shortened centre boss) E32/E34 type (differently offset centres)
- PU type ( no offset to centre mounting)

The E32 type have a soft rubber construction but also include stiffening wedges. I think that this gives good isolation under small loads but the soft movement is constrained by the wedges and the remaining movement is quite stiff. This is a good compromise in practice and I have often thought a similar approach to the rear subframe bushes might be a good scheme. Having said that the 'soft' movement in standard bushes is small anyway, before the parts of the bush hit one another.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

GazM3
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Posts: 1745
Joined: Wed Oct 26, 2011 12:55 pm
Location: Melbourne, Australia

Re: Rear Frame Bushing Removal Sucess.......

Post by GazM3 » Mon Mar 29, 2021 12:18 pm

Nice old thread revival, but I need to do this task shortly as I noticed some odd handling, went to get it aligned (as i have adjustable Kmac trailing arm bushes), but couldnt get the RHS one to a reasonable spec. Sure enough the original rubber bush has failed as the gap at the bottom of the bush is much smaller on the RHS than the LHS. Wish me luck.
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