Rear suspension knock - UPDATE

Z

Zummerset

Member
Hi guys,

After refurbing all the rear suspension on my E86, including dropping the subframe and replacing all suspension and subframe bushes, I was annoyed to find a knocking noise.

The dampers are new Bilstein B4's and I'm running new SE springs.

General consensus pointed towards the damper top mounts. Originally new Febi bilstein, I swapped to the recommended Lemforder. Still knocking.

I bought some polyurethane mounts (Bevinsee) and tried them. Still knocking and louder due to the firmer mounts.

It's definitely to do with the damper unit as a short, bouncy drive round the block with the dampers removed, there was silence.

So after 3 different top mounts and still knocking, could the dampers have an internal fault causing the noise?

Can anyone help please?
 
Are the shocks fitted the correct way? There's a bit washer built into one side of the lower bolt hole, but not the other
 
We did similar work on a friends car

A knock developed

After lots of searching we had installed the rear ARB slightly off centre and that was impacting on the arb mount

Worth a check
 
Thanks for your thoughts.
Yes, large washer on lower mount present.m and under the head of the bolt.

I'm fairly confident the arb is in the correct position. Also, thinking aloud, if there is silence when driving with the dampers removed, I don't think it can be an issue with the arb.
Cheers.
 
Thanks for your thoughts. The dust covers are new and I did try running it without them (only as a test) but the knock was still there.

It does all seem to point to faulty dampers, but both of them??

I guess to prove it I need another pair of dampers, just to try.
Anyone have some standard dampers, that still work, they would let me buy or borrow to prove the theory?
 
I have a pair off my car that I haven't yet scrapped. The dampers are shot, but they didn't knock before removal. You're welcome to collect them if you're in my neck of the woods (SL2 postcode).
 
If it's the shocks knocking, wouldn't it have been apparent when they were apart? The shaft would have to have play and there wouldn't be any pressure left (play = knackered/missing seal.)

If it's the top mounts then, particularly with the tail in the air, I'd imagine being able to give the shock a shake and replicate it
 
Watching as I seem to have this too, again with everything just replaced.
 
Appreciate the offer Triggerfish, but it looks like you are over a 4 hour round trip away. Never mind.

The dampers seem fine physically. However if there is an internal valve problem, that might not show up until under load.

Pushing the back end up and down manually doesn't replicate the noise. It's actually very difficult to get much movement of the back end by just pushing it. (And I'm over 15stone!)

Without the dampers it's easy to manually bounce the car up and down. The dampers really do add a lot of stiffness!

Appreciate all your thoughts though.
 
Also check the front differential to subframe bolt it is hard to get to once on the car but can work a little loose and knock

I know you said you drove with no damper but with a check
 
Just done a spanner check on the diff and mounting bolts, all good.

I've managed to find some supposedly ok standard dampers to try.
I should get to fit them next week.
I bet you all can't wait!
 
Zummerset said:
Just done a spanner check on the diff and mounting bolts, all good.

I've managed to find some supposedly ok standard dampers to try.
I should get to fit them next week.
I bet you all can't wait!
Click to expand...
Wouldn't describe it as riveting, but interested as I'll be fitting new parts later this year. Not enthusiastic about dealing with problems after solutions.

I've got me fingers crossed for you
 
It's also not that you got sport shocks, and they are over extended on your se spring s? (Clutching at straws there tbh, )
 
I checked the overall stroke of the damper and it more than accommodates the increased travel.
I do struggle to believe that the damper can be the correct rating for both sport and SE springs though. Bilstein says it's ok so I guess they are experts. The back end is still very firm though even with SE springs. I guess that's why the z4 doesn't 'flow' down a road like a Lotus?
 
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