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View Full Version : knocking noise from rear - bushing replacement suspected


sillycar
09-11-2008, 07:48 AM
So for about 2 years now I've heard a consistent knock when turning left and accelerating in a straight line

I have replaced the control arm, centerpiece, and done a 4 wheel alignment as well as checking the shocks/rsm, etc.

I did a search and found an excellent DIY
http://www.unitedbimmer.com/kb-e36-reartrailingarmbrushing.php

My old bushing probably looks like the one shown.

My question how much longer can I drive if I do so in a gentle manner.

I've noticed that under hard acceleration there is a throbbing/knocking from the back and it's gotten worse if I don't drive my car often

Could it be anything else needing to be fixed ... I doubt it's the bearing as there is no high-pitched noise just a knocking under any sort of acceleration more than 10 mpg

I figure it's a 2 hour job and it's going to cost at least $300

-Matt-
09-11-2008, 12:24 PM
I think your analysis is spot on RTABs are the most likely cause. If you are hearing knocking noises then the bushing has failed and the trailing arm is bashing against the cassette inside the mounting point. This is not good as any movement of the front of the trailing arm changes the camber quite a bit on the rear wheels.

ie (from rear) the wheels will be wobbling all over the place whilst you corner/accelerate:

/--\
/--/
\--\
\--/

This is not good at all and needs to be fixed (I would do it as soon as possible). However, the bolt that goes through the bushing is pretty thick - I doubt the rear of the car will collapse any time soon if you drive carefully. The problem is that the side to side impact might bent the mounting cassette (or worse rip out the thread). You are definitely going to need an alignment after the bushings are replaced.

The very worst case would be that the lack of cushioning could cause damage to the mounting points (on the actual chassis) - and apparently this is quite a common fail point.

RacingGreen
09-12-2008, 06:06 AM
If when you go over a pot hole in the road or a draincover or something similar you hear a loud knocking sound from just in front of the rear axle (in my case). It was the rear trailing arm bush's and sounds as though you've got exactly the same problem. 30 for a pair from BMW, but you need a special equipment (hydraulic press) to change them. You definately need to get it done as if on the rear it will bugger up the tracking and wear your tyres down as well. 2/3 hour job with the right kit.

Its a coincidence. The first and only thing I did to my car which I bought last month was replace those. How many miles has your car done out of interest?

sillycar
09-12-2008, 07:59 AM
Also another effect is shuddering when braking

When I did my alignmnet, luckily the bolts hadn't seized but he did mention something was bent on the rear wheel and he couldn't fix it without me changing several parts

I think it's from me driving like a nascar idiot changing to 2nd gear at 30 mph spinning the tires and fishtailing everywhere

I have about 168 000 miles just thinking of keeping it for one more year before i get a new bmw

I change my tires every year at about $160 for all 4 used - I have definite cupping and shredding problems

Also another problem related to hard cornering is my steering rack. I had a slow leak that developed into a fast leak and if I need to change that i'm in trouble

miked0461
09-12-2008, 08:06 AM
ive had the same problem man, accellerating it sounds like there something banging up and down against the underside of the car, and its also noticable when turning left. cant for the life of me figure out what it is. took it to my buddies shop and he couldnt figure it out either