M40i brakes - design flaw uncovered

Jim S · Post by **Jim S** » Sun Nov 17, 2024 4:35 pm

Just wondering if BMW has finally upgraded the heat shields on the M Sport front brakes? Are any new G29 M40i owners willing to post a recent photo of their brakes and compare it to the one that I posted on Page 3 of this thread. See link below.

viewtopic.php?p=1657203#p1657203

hairyfrogowl · Post by **hairyfrogowl** » Thu Feb 27, 2025 9:50 pm

Well, after 7k (joyous) miles in the M40i, today the dreaded stone in brakes demon struck!

Due to some roadworks I took a detour down some admittedly crappy roads and after a while noticed a weird noise. At first I wasn't sure whether it was just some debris stuck under the wheel arch - it wasn't that loud but after a few miles the dreaded squeal set in.

I learned a few things from this
- when you really need to do some stamping on the brakes in a quiet place every man and his dog turn up to prevent you doing so!
- my ABS work well

So yeah, some heavy braking got rid of it thankfully but not a pleasant experience. It will certainly make me think twice about "off-roading" again any time soon, at least whilst the roads are so muddy/crappy.

Car is due a service soon so will mention it to BMW to see if they have any thoughts about solutions/whether the rumours of a fix are true.

May your miles be stone free

Jim S · Post by **Jim S** » Sat Mar 08, 2025 10:34 am

I know your pain well. Sounds horrific.

Zed Baron · Post by **Zed Baron** » Sat Mar 08, 2025 11:03 am

I got caught out a couple of weeks ago with it, took the other half up to the stables and it sounded like the heat shield being torn off coming out the car park! All the rubbish on the roads, loose stones etc. after a heavy storm.

Nanu · Post by **Nanu** » Sat Mar 08, 2025 9:31 pm

To save me going back over 19 pages, is this issue just on the M40s or all G29s with the sport brakes?

B21 · Post by **B21** » Sat Mar 08, 2025 10:32 pm

Nanu wrote: Sat Mar 08, 2025 9:31 pm To save me going back over 19 pages, is this issue just on the M40s or all G29s with the sport brakes?

I imagine to a lesser or greater extent it affects most modern BMWs ..they’ve changed the design logic on the dust shield….almost all now act as an air scoop rather than just as a dust shield..

Scubaregs · Post by **Scubaregs** » Sun Mar 09, 2025 11:14 am

I had it on my 30i. Picked up a stone in company car park. Tried for days to dislodge it to no avail, evenyually it was wheel off.

Zed Baron · Post by **Zed Baron** » Sun Mar 09, 2025 3:45 pm

Nanu wrote: Sat Mar 08, 2025 9:31 pm To save me going back over 19 pages, is this issue just on the M40s or all G29s with the sport brakes?

My niece had the same problem on her 5 series

Nanu · Post by **Nanu** » Sun Mar 09, 2025 7:37 pm

Scubaregs wrote: Sun Mar 09, 2025 11:14 am I had it on my 30i. Picked up a stone in company car park. Tried for days to dislodge it to no avail, evenyually it was wheel off.

Cheers. So far so good then

bleatoid · Post by **bleatoid** » Thu Apr 24, 2025 11:09 pm

Yep - we had this happen today and I reckon Jim's theory is correct re the centrifugal force - hissing / squealing started just after slowing down at a roundabout and the racket was horrendous though strangely intermittent after that. Fortunately we were 3 miles from home - called BMW roadside assist and the guy knew immediately what the issue was.

I've got the M performance brakes on my 4 series and never had an issue in 3 1/2 years - the M40i we've only had for 3 months.....at least we know what it is and how to fix it next time - or would, if we had a jack...

Jim S · Post by **Jim S** » Fri Apr 25, 2025 10:22 am

bleatoid wrote: Thu Apr 24, 2025 11:09 pm Yep - we had this happen today and I reckon Jim's theory is correct re the centrifugal force - hissing / squealing started just after slowing down at a roundabout and the racket was horrendous though strangely intermittent after that. Fortunately we were 3 miles from home - called BMW roadside assist and the guy knew immediately what the issue was.

I've got the M performance brakes on my 4 series and never had an issue in 3 1/2 years - the M40i we've only had for 3 months.....at least we know what it is and how to fix it next time - or would, if we had a jack...

Yes, the noise is horrendous. Thought BMW might have come up with a fix by now. 6 years since it first happened to me.

I bought a cheap scissor jack and extended wheel nut wrench and socket in the boot of my car so that I could remove the wheel and stone if I needed to. Used it one time, the other times I either managed to “drive” it out or called in BMW.

Jim S · Post by **Jim S** » Fri Apr 25, 2025 10:23 am

Jim S wrote: Fri Apr 25, 2025 10:22 am
bleatoid wrote: Thu Apr 24, 2025 11:09 pm Yep - we had this happen today and I reckon Jim's theory is correct re the centrifugal force - hissing / squealing started just after slowing down at a roundabout and the racket was horrendous though strangely intermittent after that. Fortunately we were 3 miles from home - called BMW roadside assist and the guy knew immediately what the issue was.

I've got the M performance brakes on my 4 series and never had an issue in 3 1/2 years - the M40i we've only had for 3 months.....at least we know what it is and how to fix it next time - or would, if we had a jack...
Yes, the noise is horrendous. Thought BMW might have come up with a fix by now. 6 years since it first happened to me.
I bought a cheap scissor jack and extended wheel nut wrench and socket and kept it in the boot of my car so that I could remove the wheel and stone if I needed to. Used it one time, the other times I either managed to “drive” it out or called in BMW.

Jim S · Post by **Jim S** » Sat Apr 26, 2025 5:06 pm

Jim S wrote: Fri Apr 25, 2025 10:22 am
bleatoid wrote: Thu Apr 24, 2025 11:09 pm Yep - we had this happen today and I reckon Jim's theory is correct re the centrifugal force - hissing / squealing started just after slowing down at a roundabout and the racket was horrendous though strangely intermittent after that. Fortunately we were 3 miles from home - called BMW roadside assist and the guy knew immediately what the issue was.

I've got the M performance brakes on my 4 series and never had an issue in 3 1/2 years - the M40i we've only had for 3 months.....at least we know what it is and how to fix it next time - or would, if we had a jack...
Yes, the noise is horrendous. Thought BMW might have come up with a fix by now. 6 years since it first happened to me.
I bought a cheap scissor jack and extended wheel nut wrench and socket and kept it in the boot of my car so that I could remove the wheel and stone if I needed to. Used it one time, the other times I either managed to “drive” it out or called in BMW.

sars · Post by **sars** » Mon Apr 28, 2025 8:32 pm

So it happened to me today, did not have any issues for the first three years and now twice in the space of six months. Solved by reversing and braking hard and repeat.

It really is the worst sound in the world

hairyfrogowl · Post by **hairyfrogowl** » Tue Apr 29, 2025 9:18 am

I feel your pain. Always seems to happen to me when there's loads of traffic making braking and reversing somewhat challenging

Z4-forum.com

Z4-forum.com