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2019+ BMW 3 AND 4-SERIES FORUMS (G2x Generation) General G20 Sedan / G22 Coupe / G26 Gran Coupe Discussions Stones trapped in M Sport brakes

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      07-15-2019, 06:03 AM   #1
Jim S
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Stones trapped in M Sport brakes

Have any new g20 owners experienced a problem with stones getting trapped in the front M Sport brakes?

I have a new g29 Z4 which has the exact same M Sport brakes design as the g20 and stones are regularly getting trapped in my front brakes. This has happened to me five times in the first 12 weeks of ownership. Some other g29 owners have experienced the same problem. The stone gets trapped between the shield and brake disc and it sounds absolutely horrendous.

I would be interested to hear whether or not any g20 owners with M Sport brakes have experienced the same problem.
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      07-15-2019, 09:48 AM   #2
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I have an F30 with Sport Brakes, it happened once.
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      07-15-2019, 10:11 AM   #3
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Originally Posted by Jbrock22 View Post
I have an F30 with Sport Brakes, it happened once.
Thanks for your feedback jbrock22. I am trying to get BMW to fix the very poor design of the front shields as they are a magnet for trapping stones. The more owners that the report the problem the better.
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      07-15-2019, 10:32 AM   #4
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The photograph below highlights the problem.

This is the front M Sport brake assembly on the G29 Z4, which is identical to the new G20 3 series with M Sport brakes. The wide open top is like an open mouth and a magnet to attract stones and the bottom of the shield bends inwards towards the brake disc closing the gap and traps the stone. You will also see that the bottom of the shield is positioned hard up against the track rod end and therefore can’t be bent outwards to increase the size of the gap to let the stone escape.
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      07-15-2019, 11:01 AM   #5
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All M brakes have that issue. If you drive on stones with sticky tires it will happen. I used to cut those back plates off. You really don't need them.
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      07-15-2019, 11:08 AM   #6
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Originally Posted by Ilyam5 View Post
All M brakes have that issue. If you drive on stones with sticky tires it will happen. I used to cut those back plates off. You really don't need them.
Thanks for your input Ilyam5. I may end up doing that but at the moment the car is under warranty for 3 years.
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      07-15-2019, 11:42 AM   #7
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It looks like BMW designed these new shields to be able to come out without removing the wheel bearing. You just need to remove the rotor and caliper. Maybe you can just ask the dealer to do that if you can't do that yourself. I doubt it would void any warranty. Obviously during testing, they probably don't expect most people who need to drive on gravel/stony roads to get the M Performance version of the car. In your particular situation, they might be fine with you removing them.
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      07-15-2019, 11:48 AM   #8
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Originally Posted by upsidedownfunnel View Post
It looks like BMW designed these new shields to be able to come out without removing the wheel bearing. You just need to remove the rotor and caliper. Maybe you can just ask the dealer to do that if you can't do that yourself. I doubt it would void any warranty. Obviously during testing, they probably don't expect most people who need to drive on gravel/stony roads to get the M Performance version of the car. In your particular situation, they might be fine with you removing them.
The problem is happening on main roads with some pot holes and a few stones, not gravel tracks or back roads. I have an ongoing issue with BMW to try to get the problem resolved on my car. Removing the shields may be the outcome, without voiding the warranty.

Thanks for your input.
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      07-15-2019, 06:55 PM   #9
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Quote:
Originally Posted by Jim S View Post
The problem is happening on main roads with some pot holes and a few stones, not gravel tracks or back roads. I have an ongoing issue with BMW to try to get the problem resolved on my car. Removing the shields may be the outcome, without voiding the warranty.

Thanks for your input.
Can you bend the bottom of the shields away slightly from the rotor to allow the stone(s) to fall out?
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      07-16-2019, 05:46 AM   #10
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Quote:
Originally Posted by Jbrock22 View Post
Can you bend the bottom of the shields away slightly from the rotor to allow the stone(s) to fall out?
No, because the bottom of the shield is very close to the track rod end.
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