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Banging noise from the rear

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Rathean
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Posts: 133
Joined: Thu May 19, 2016 10:49 pm

Banging noise from the rear

Post by Rathean » Tue Jul 31, 2018 2:30 pm

So I've recently had the rear springs replaced after one of them snapped going over a small crater that was posing as a pothole. That fixed the metal on metal grating but the car now 'thumps' over uneven road surfaces. The bang sounds are also coming from the rear, any ideas what it could be - please don't say dampers :(
2011 X3 30d MSport black, 8-speed auto, leather everything
2011 Bimmer Z4 35i diamond black, 6-speed manual, full caboodle (hibernating) :driving:

andystone
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Location: Near Carmarthen

Banging noise from the rear

Post by andystone » Tue Jul 31, 2018 4:47 pm

Following. I have a knock which has worsened since changing my rtab’s.
2005 e85 z4, 2.5

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flybobbie
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Joined: Sat May 25, 2013 8:27 pm
Location: Stourbridge

Banging noise from the rear

Post by flybobbie » Tue Jul 31, 2018 7:15 pm

When i first had my Z4 there was a banging noise from the rear right side, sounded like someone hitting the underside with a rubber mallet.
Took me nine months to cure and two unsuccessful visits to BMW dealers (So much for warranties), after i replaced the anti roll bar bushes for poly and replaced worn out standard shocks with Bilsteins.
I finally cured the problem by rotating the spring so that the number and letter printed on the spring went from outboard to the front.
Never had a noise since.

Apparently by chance i came across a BMW technical advisory from some earlier BMW models that had a problem with knocking. It suggested applying talcum powder to the rubbers at each end of spring, which it sits on. Which i was i did.
I removed the spring, washed the rubbers, applied talc then reassembled, but by mistake positioned the spring 90 anticlockwise when refitted. All this cured the noise. The tech bulletin suggested the barrel springs were gripping the rubbers and rebounding.
I think the barrel spring is a poor design. They compress in an arc. Unlike the front springs. It takes too much load on one side over a small area, hence earlier models breaking and as the compress the ends tighten and grip the rubbers causing a rebound.

Rathean
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Posts: 133
Joined: Thu May 19, 2016 10:49 pm

Banging noise from the rear

Post by Rathean » Wed Aug 01, 2018 12:56 pm

So problem solved, the rear springs had been fitted incorrectly causing one of the springs to catch the bodywork on the downward oscillation after going over a bump. Sorry I'm not more mechanically minded than that other to say it took them half an hour to refit to ensure the rubber stoppers where correctly positioned... no more rubber mallet sounds over uneven surfaces.

Hope that helps others 8)
2011 X3 30d MSport black, 8-speed auto, leather everything
2011 Bimmer Z4 35i diamond black, 6-speed manual, full caboodle (hibernating) :driving:

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