M40i brakes - design flaw uncovered

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Wyldie85
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M40i brakes - design flaw uncovered

Post by Wyldie85 » Mon Nov 25, 2019 11:09 pm

Swiftly wrote:
Mon Nov 25, 2019 8:13 pm
So far I have yet to experience this issue, but am holding my breath as I guess it's just a matter of time before it happens to mine :cry:
Same and same,
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bonzo
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M40i brakes - design flaw uncovered

Post by bonzo » Tue Nov 26, 2019 11:24 am

I've had the discs checked and BMW have reported that all is fine - which is good news. I'm surprised that such a dramatic noise has resulted in no damage but there you go.

When it happens again I'll ring BMW UK (for the third time) explain that I've had my local dealer check the disc and, more importantly, ask why my dealer believes no one else has reported this issue despite that not being the case.

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M40i brakes - design flaw uncovered

Post by Samiad » Sat Jan 11, 2020 7:08 am

Surprised myself today by getting this issue in my front right corner. I don’t have the m brakes though, so I was surprised as I assumed it was an m brake issue only, but I guess the same design flaw is present in the non-m brakes.

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M40i brakes - design flaw uncovered

Post by Jim S » Sat Jan 11, 2020 3:13 pm

Samiad wrote:
Sat Jan 11, 2020 7:08 am
Surprised myself today by getting this issue in my front right corner. I don’t have the m brakes though, so I was surprised as I assumed it was an m brake issue only, but I guess the same design flaw is present in the non-m brakes.
Not sure what the heat shields look like on the non M Sport brakes. If you look at page 3 of this thread you will see photos of my M Sport brakes, which clearly show the reason why stones easily get trapped. :driving:

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M40i brakes - design flaw uncovered

Post by Z4monster » Sat Jan 11, 2020 4:50 pm

Had this once in 5000 miles. It made a hell of a screech and I did wonder what the hell had happened at first. Once I stopped and reversed a few feet, it came loose and fell out. No problem since.
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M40i brakes - design flaw uncovered

Post by john-e89 » Sat Jan 11, 2020 6:30 pm

Jim S wrote:
Sat Jan 11, 2020 3:13 pm
Samiad wrote:
Sat Jan 11, 2020 7:08 am
Surprised myself today by getting this issue in my front right corner. I don’t have the m brakes though, so I was surprised as I assumed it was an m brake issue only, but I guess the same design flaw is present in the non-m brakes.
Not sure what the heat shields look like on the non M Sport brakes. If you look at page 3 of this thread you will see photos of my M Sport brakes, which clearly show the reason why stones easily get trapped. :driving:
How do you reckon they’re getting in there Jim..? Looking at the wheels I’m thinking passing cars flicking them into your wheels which roll them around until they fall out the back at just the right, or wrong, moment..?
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Jim S
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M40i brakes - design flaw uncovered

Post by Jim S » Sat Jan 11, 2020 6:48 pm

john-e89 wrote:
Sat Jan 11, 2020 6:30 pm
Jim S wrote:
Sat Jan 11, 2020 3:13 pm
Samiad wrote:
Sat Jan 11, 2020 7:08 am
Surprised myself today by getting this issue in my front right corner. I don’t have the m brakes though, so I was surprised as I assumed it was an m brake issue only, but I guess the same design flaw is present in the non-m brakes.
Not sure what the heat shields look like on the non M Sport brakes. If you look at page 3 of this thread you will see photos of my M Sport brakes, which clearly show the reason why stones easily get trapped. :driving:
How do you reckon they’re getting in there Jim..? Looking at the wheels I’m thinking passing cars flicking them into your wheels which roll them around until they fall out the back at just the right, or wrong, moment..?
Yes John, I think you are on the right track. From my experiences my theory is that the stones are getting onto the inside rim of the wheel somehow and are being held there by centrifugal force until you slow down and they drop into the gap between the brake heat shield and rotor. In the six times that it has happened to me, on main roads I must add, the problem occurred either when I was coming to a stop or taking away from standstill. This would back up my theory that the stones are entering the brakes when the car is going slow. :headbang:
Last edited by Jim S on Sat Jan 11, 2020 7:33 pm, edited 1 time in total.

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M40i brakes - design flaw uncovered

Post by Jim S » Sat Jan 11, 2020 7:32 pm

On a positive note. If I could give any owners who experience this horrendous sounding problem some advice. If you hear a loud screeching noise coming from your wheel, stop the car as soon as you can and reverse a few yards as this may throw out the stone before it gets lodged too far into the brakes. Remember that you are likely to be going slow at this point. Once the stone gets right down into the gap between the shield and rotor it is almost impossible to get it out without removing the wheel.

Hope this helps. :thumbsup:

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M40i brakes - design flaw uncovered

Post by Obs-Com » Tue Jan 28, 2020 5:13 pm

Been wondering about this issue having read the posts. No events to report on my G29 - until today!

Had a meeting over in Liverpool this morning. On leaving the car park area I heard small, loose gravel being thrown at very low speed by the wide Michelins. Not unusual and no issue. However, 5 minutes later a screeching noise was heard from the front nearside wheel. Having read the experience of others I knew exactly what this was. As I was in slow traffic I had no option but to keep going. Fortunately the responsible stone dislodged after 50/60 yards and no further issues.

I now understand the experience of others and it's quite a noise when a stone becomes trapped. Don't think a trip to the dealership is required but will be checking it out in more detail over coming days. Given there have now been quite a few reports of this issue it will be worth reporting any similar experiences on Forum cars and keeping an eye for any feedback from BMW.

Aside from the above, I continue to be very impressed by the all round ability of the M40i each time I drive it. A very quiet and smooth motorway cruiser and well balanced and a very capable sports car when wanted.
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2019-??: G29 M40i First Edition (more stunning than the M2)

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M40i brakes - design flaw uncovered

Post by Jim S » Tue Jan 28, 2020 5:36 pm

Obs-Com wrote:
Tue Jan 28, 2020 5:13 pm
Been wondering about this issue having read the posts. No events to report on my G29 - until today!

Had a meeting over in Liverpool this morning. On leaving the car park area I heard small, loose gravel being thrown at very low speed by the wide Michelins. Not unusual and no issue. However, 5 minutes later a screeching noise was heard from the front nearside wheel. Having read the experience of others I knew exactly what this was. As I was in slow traffic I had no option but to keep going. Fortunately the responsible stone dislodged after 50/60 yards and no further issues.

I now understand the experience of others and it's quite a noise when a stone becomes trapped. Don't think a trip to the dealership is required but will be checking it out in more detail over coming days. Given there have now been quite a few reports of this issue it will be worth reporting any similar experiences on Forum cars and keeping an eye for any feedback from BMW.

Aside from the above, I continue to be very impressed by the all round ability of the M40i each time I drive it. A very quiet and smooth motorway cruiser and well balanced and a very capable sports car when wanted.
I am sorry to hear that but not surprised since it has happened to me six times now in 3,000 miles. :thumbsdown:

Lucky for you that the stone came out fairly quickly. If it gets right down into the gap between the rotor and shield it is almost impossible for it to come out and you need to remove the wheel to get at the stone. I now carry a scissor jack and an extending wheel brace in my boot for this purpose. :headbang:

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M40i brakes - design flaw uncovered

Post by Obs-Com » Tue Jan 28, 2020 5:50 pm

Cheers Jim. I was looking for a place to pull over or turn out of the traffic so I could try the reverse dislodge technique. Luckily the stone dislodged itself very quickly. No harm done (this time) but quite a noise!

I do recall a similar problem quite a few years ago in a previous E93. I was on a French country road that had been recently covered in gravel and some of the stones became trapped touching the brake disc. Very similar noise but louder!
2011-14: E89 2.3sDrive
2014-16: E89 35is - Valencia Orange X2 (gone but not forgotten)
2016-17: F33 440i
2017-17: E85 2.5si
2017-19: F87 M2 - Long Beach Blue DCT (Stunning)
2019-??: G29 M40i First Edition (more stunning than the M2)

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