Preventing Damper Bush Failures

Repository of 'how to do' articles relating to the Z3 and M roadster/coupe
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Preventing Damper Bush Failures

Post by Guest »

From time to time we hear of a Z3 owner who has found that their rear dampers have become disconnected from the trailing arms. To be exact, the circular ‘eye’ at the base of the damper slides off its rubber bush, leaving the rubber bush and securing bolt in position.

In every case, the dampers have been replaced and the original dampers simply discarded. In such cases no-one has noticed that the steel bushes in the base of the original unit have a flat rectangular flange at the end against the bolt head.
Even when this is noticed, few people realise its function, which is to prevent the damper ‘eye’ working its way out of position in the event of the rubber bush separating from the damper.

The result is that in the event of the rubber bush separating, the damper ‘eye’ will work its way over the bush, and disengage, with the result that damping is totally lost.
The answer, of course, is to remove the original steel bush and fit it to the new damper, which is quite an easy task, given a vice and some basic tools.
To remove the original bush, grip the sides of the flange in the edge of your vice jaws, insert an M12 socket screw into the hole, and arrange a two-legged puller so that its legs engage behind the damper ‘eye’ and rubber, with its screw pressing against the head of the socket screw. Turning the forcing screw will therefore draw the rubber bush off the steel bush.

Fitting the original steel bush into the new damper is just as easy – set the new damper in the vice jaws, with the circular end of the original steel bush pressing against one end of the new steel bush. Fit a suitable piece of tube – or a socket – over the other end of the original steel bush. Tighten the vice jaws until the old bush/new bush/socket combination is rigidly held, and check that they are all in line with each other – an assistant is useful here.

When you are happy with the alignment, tighten the vice until the original steel bush has forced the new bush out of its rubber and into the socket/tube, when the job is done.
In the event of a bonding failure, your damper will stay – more or less – in position, at the expense of a few rattles, but it’s not as exciting as suddenly losing damping at one corner.

Such failures are very unusual, but certainly not unknown, particularly on dampers which are both cheap and firm, where the bonding of the rubber leaves something to be desired, and is also under severe stress.
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c_w
Joined: Thu 19 Aug, 2004 16:50
Posts: 4032

  M roadster S50

Post by c_w »

Not sure why anything other but OE dampers don't have these on but I've just used big washers on mine.
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Washers

Post by Guest »

Yes - if you can get washers of the correct size - and thickness - they would work well enough. Ideally, find a friend who has a lathe. Otherwise, this only takes a few minutes work, and the job's done.

I wouldn't be surprised if the bush/plate idea is patented by BMW, making me rather like BMW's idea finding its way onto Bilstiens!
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