Deep "clunk" noise from rear on my M4

[JCHill]

Interesting day today.

Dropped my M4 in to the dealership to have an intermittent clunk noise at the rear of the car investigated.

It's a strange one that tends to appear on poor road surfaces, from time to time.

This isn't the well documented 'scraping' sound of stones stuck in the brake disc guard. This a deep 'clunk' noise that, from the drivers seat, sounds to be coming from near-side rear.

Long story short: The dealership managed to recreate the noise but not fix it. PuMA raised with BMW and it turns out it's a documented issue but with no solution yet.

Anyone else having this problem?

[molar explorer]

I had this problem on my convertible and also a host of other issues that were referred to bmw who said there was no current fix and would call me when there was. This was 12 months ago and in the end I got so frustrated with the car I sold it. I hope you have more success than I did!

[NORTS]

Could be the LSD?

[Wills2]

No not had that sound, I get the occasional stone in the disk guard but not the clunking. (thank god!)

[JCHill]

NORTS said:

Could be the LSD?

To be honest it doesn't sound diff-related. I'm ok with the soft thud which you sometimes get from the rear diff when engaging gears / disengaging gears / rolling-on power / rolling-off power. That's more of an expected 'smooth' sound from gears bathed in oil. This sounds more like hard metal hitting hard metal...if you get my meaning?

I've done a bit more playing around, trying to isolate the cause and I'm thinking it's movement in the rear brake-pads...possibly? The reason is that when I apply a slight touch of the brake, to take away any movement in the braking system, on a surface I can guarantee will normally create the noise, the noise goes away.

The car's only 6 months old so I'm loathed to strip down the brakes to investigate further. So I'm thinking that the next step is to have another chat with the dealership and see what they come back with.

Edited by JCHill on Wednesday 30th March 15:01

Edited by JCHill on Wednesday 30th March 15:01

[JCHill]

molar explorer said:

I had this problem on my convertible and also a host of other issues that were referred to bmw who said there was no current fix and would call me when there was. This was 12 months ago and in the end I got so frustrated with the car I sold it. I hope you have more success than I did!

I hope so to! So far this is the only issue...fingers crossed.

[MWM3]

Could it be a bad bump stop? Saying that, that should be obvious to the dealer.

[JCHill]

Spoke to dealership, they confirmed it's the rear brakes that they've raised the PuMA for.

I've managed to recreate it...

http://youtu.be/P0igl6z8uyI

[Foretrees]

That's a noise I heard a few times over the first few days, it's seems to have stopped, like a metallic click, so much so I was out under the car rumbling the exhaust around to see if it was loose, I thought it might have been a heat sheild noise but that sounds very similar, have they suggested a fix? Thanks John

[dufflecoat]

Had this on my e92. Definitely brake related, in the end I narrowed it down to the hand brake auto adjustment mechanism. Came and went but never caused a problem.

[JCHill]

Foretrees said:

That's a noise I heard a few times over the first few days, it's seems to have stopped, like a metallic click, so much so I was out under the car rumbling the exhaust around to see if it was loose, I thought it might have been a heat sheild noise but that sounds very similar, have they suggested a fix? Thanks John

No fix yet but, to be fair, it's only been a few days and I doubt that the internal wheels at BMW turn quite as quickly as those on their cars!

I am preparing myself for a "That's expected behaviour" response but my thoughts today are that I'm not going to accept that (the front pads don't do it, my F10 M5 didn't do it either) but let's wait and see what they say.

Glad to read that it's not just me though!

[Foretrees]

Thanks, I am due the 1200mls service soon I will also mention to the service manager, just to see if they have heard of this and have any ideas, like you say they won't have much of an idea, thanks John

[ZP]

Our M3 does it too.
Also get a very intermittent (could be weeks between instances) scraping noise.
All very odd.

[JCHill]

Foretrees said:

Thanks, I am due the 1200mls service soon I will also mention to the service manager, just to see if they have heard of this and have any ideas, like you say they won't have much of an idea, thanks John

No problem, best of luck. It's incredibly easy to demonstrate, if needed, by just pushing the brake pad upwards (see my YouTube clip above) and letting it 'clung' back into position.

[JCHill]

ZP said:

Our M3 does it too.
Also get a very intermittent (could be weeks between instances) scraping noise.
All very odd.

I'm not surprised. I truly don't understand why there's so much travel designed into the rear pad / rear caliper without some kind of retaining clip to stop the two parts knocking together...weird.

Scraping could be the 'stones in the grit guard' problem. I understand that the DIY fix is to push the guard away from the disc a little to allow bigger stones to escape and not get trapped. Fortunately I've not (yet) experienced this problem.

[ZP]

I've had the stone guard issue several times - this other scraping noise is different.
Almost like something's dragging on the Tarmac, but only lasts a second or two at most.

[JCHill]

ZP said:

I've had the stone guard issue several times - this other scraping noise is different.
Almost like something's dragging on the Tarmac, but only lasts a second or two at most.

That is weird. But to last that length of time sounds like some kind of obstruction which eventually clears. Might be worth examining wheel / tyre / disc / pad / caliper / wheel-arch area but other than that I'm struggling to think what it could be...

[helix402]

I reckon they'll be a redesign for the rear brake pads before too long. Just checked, they've been changed once already. No 4 could be a culprit too:

Edited by helix402 on Sunday 3rd April 13:01

[JCHill]

helix402 said:

I reckon they'll be a redesign for the rear brake pads before too long. Just checked, they've been changed once already. No 4 could be a culprit too:

Perfect! Thanks for posting!

Totally agree with you...from what I'm seeing No. 4 needs more tension and/or the pad guide hole diameters need a closer match with their retaining pins (No. 3) to reduce the amount of play.

[helix402]

Glad to help, let us know when it's sorted.