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Wulliem12 wrote: ↑Tue Feb 22, 2022 4:38 pm This happened to me last month, hadn’t joined here so didn’t know what it was, really loud squealing. I’ve had stones stuck before on other cars, but never as loud as this. Called the garage where I got it from, they said bring it up (40min journey), I said I wasn’t going to drive it, didn’t know what damage was being done. Cut a long story short, picked up on low loader through BMW assist. Taken to closer BMW dealership, big stone taken out and charged £108. Fast forward a few weeks later and another stone, not as loud as the first one (had just joined here), saw this thread and thought, jees, new car with a hidden design fault, great! Was parked up at work, finished work came out, went into reverse (like suggested on here) didn’t have to it must have dropped out when stationary. Anyway, think I will have to annoy the dealership where I got it from, I aint paying over a hundred pounds each time a stone gets stuck, ridiculous!
Seen a few suggestions for do it yourself, anyone have a sure fire way that doesn’t involve taking the wheel off etc. (would do if really necessary).

Wulliem12 wrote: ↑Tue Feb 22, 2022 4:38 pm This happened to me last month, hadn’t joined here so didn’t know what it was, really loud squealing. I’ve had stones stuck before on other cars, but never as loud as this. Called the garage where I got it from, they said bring it up (40min journey), I said I wasn’t going to drive it, didn’t know what damage was being done. Cut a long story short, picked up on low loader through BMW assist. Taken to closer BMW dealership, big stone taken out and charged £108. Fast forward a few weeks later and another stone, not as loud as the first one (had just joined here), saw this thread and thought, jees, new car with a hidden design fault, great! Was parked up at work, finished work came out, went into reverse (like suggested on here) didn’t have to it must have dropped out when stationary. Anyway, think I will have to annoy the dealership where I got it from, I aint paying over a hundred pounds each time a stone gets stuck, ridiculous!
Seen a few suggestions for do it yourself, anyone have a sure fire way that doesn’t involve taking the wheel off etc. (would do if really necessary).

Jim S wrote: ↑Sat Jun 01, 2019 3:55 pm I think I may have uncovered a design flaw in the M Sport brakes fitted to the new Z4 M40i and other Z4 G29 models fitted with the same brakes. Stones are far too easily getting trapped between the brake disc rotor and the metal heat/protector shield behind the rotor.

In the space of only a few weeks and 800 miles of taking delivery of my brand new Z4 M40i this problem has occurred four times. When it happens it sounds absolutely horrendous. The noise is a very loud high pitched squeal and it sounds like the wheel is just about to fall off. I have also noticed that it usually only happens when the car is slowing down close to stopping. I have a theory for this, which I will explain later.

There is no jack in the car to lift up the wheel to see where the stone is trapped and you either need to try to free it by driving, sometimes several miles and causing damage by scoring the disc rotor, or call out the BMW breakdown service.

In many years of motoring in BMW's and several other brands of cars this is the first time I have ever experienced such a problem. I believe that there is a fundamental design flaw in the structure of the M40i brakes as I will explain below.

Most modern cars have disc brakes and they can develop a lot of heat so the manufacturers incorporate a metal shield right behind the brake rotor to prevent unwanted heat transfer to brake pipes, ball joints and other heat sensitive parts of the car. The shield is also there to prevent stones, debris, water and dirt getting into the brake assembly. Normally, this shield is bent over the top of the rotor to close off the gap where debris and stones can fall into the brake assembly. On the M40i both the front and rear metal shields do not bent over the rotors. In fact the front ones actually bend away from the rotor creating an even bigger gap for stones and debris to fall into the brake assembly. The gap is large enough for small stones and debris to pass through but anything larger than about 1cm (1/2”) in size is likely to get trapped, causing the problem that I am describing in this review.

In the UK, many of the roads are covered in stones washed up out of pot holes and decaying road surfaces so it is very difficult to avoid getting stones thrown up into the wheel arches of our cars. I have also noticed that the Z4 M40i is very prone to throwing up stones and this might have something to do with the 19" Michelin Pilot Super Sport Performance tyres. These two things are exacerbating the problem.

On examining the location of the brake rotors on the M40i it is difficult to understand how the stones are getting into the rotors as the wheel rims are extremely wide and the rotor assembly is near the centre of the rim. Also, the rotors are quite large in diameter so the space between the top of the rotor and wheel rim is quite small, making it very difficult for stones or debris to get thrown directly into the brake assembly.

My theory is that some stones are being thrown onto the wheel rims and the centrifugal force of the wheels rotating causes the stones to stay on the wheel rim until the car slows down at which point they fall down into the gap between the brake rotor and metal shield. Any stone or debris larger than about 1cm is likely to get trapped, particularly since the design of the metal shield does not prevent the stones and debris getting into the brake assembly as it should.

I believe that the problem outlined above is a design flaw in the Z4 M40i brakes and BMW should stand up and take responsibility and offer an immediate remedy for the affected cars. I have already requested my Dealer to take this issue up with BMW.

I would like to hear if any other Z4 G29 owners have had similar problems with their car.

Jim S wrote: ↑Tue Feb 22, 2022 4:54 pm

Wulliem12 wrote: ↑Tue Feb 22, 2022 4:38 pm This happened to me last month, hadn’t joined here so didn’t know what it was, really loud squealing. I’ve had stones stuck before on other cars, but never as loud as this. Called the garage where I got it from, they said bring it up (40min journey), I said I wasn’t going to drive it, didn’t know what damage was being done. Cut a long story short, picked up on low loader through BMW assist. Taken to closer BMW dealership, big stone taken out and charged £108. Fast forward a few weeks later and another stone, not as loud as the first one (had just joined here), saw this thread and thought, jees, new car with a hidden design fault, great! Was parked up at work, finished work came out, went into reverse (like suggested on here) didn’t have to it must have dropped out when stationary. Anyway, think I will have to annoy the dealership where I got it from, I aint paying over a hundred pounds each time a stone gets stuck, ridiculous!
Seen a few suggestions for do it yourself, anyone have a sure fire way that doesn’t involve taking the wheel off etc. (would do if really necessary).

I know your pain. Happened to me six times now. Once that stone gets right down into the gap between the disc and heat shield it is almost impossible to get out without taking the wheel off or getting the car up onto a ramp unless you are lucky enough for it to break up whilst driving the car.

By the way, I was the one who opened this thread very early on to make others aware of this problem. Seems like BMW are not interested in altering the design to resolve the problem. Very poor show BMW.

Jim S wrote: ↑Tue Feb 22, 2022 4:54 pm

Wulliem12 wrote: ↑Tue Feb 22, 2022 4:38 pm This happened to me last month, hadn’t joined here so didn’t know what it was, really loud squealing. I’ve had stones stuck before on other cars, but never as loud as this. Called the garage where I got it from, they said bring it up (40min journey), I said I wasn’t going to drive it, didn’t know what damage was being done. Cut a long story short, picked up on low loader through BMW assist. Taken to closer BMW dealership, big stone taken out and charged £108. Fast forward a few weeks later and another stone, not as loud as the first one (had just joined here), saw this thread and thought, jees, new car with a hidden design fault, great! Was parked up at work, finished work came out, went into reverse (like suggested on here) didn’t have to it must have dropped out when stationary. Anyway, think I will have to annoy the dealership where I got it from, I aint paying over a hundred pounds each time a stone gets stuck, ridiculous!
Seen a few suggestions for do it yourself, anyone have a sure fire way that doesn’t involve taking the wheel off etc. (would do if really necessary).

I know your pain. Happened to me six times now. Once that stone gets right down into the gap between the disc and heat shield it is almost impossible to get out without taking the wheel off or getting the car up onto a ramp unless you are lucky enough for it to break up whilst driving the car.

By the way, I was the one who opened this thread very early on to make others aware of this problem. Seems like BMW are not interested in altering the design to resolve the problem. Very poor show BMW.

Obs-Com wrote: ↑Tue Feb 22, 2022 5:10 pm

Wulliem12 wrote: ↑Tue Feb 22, 2022 4:38 pm This happened to me last month, hadn’t joined here so didn’t know what it was, really loud squealing. I’ve had stones stuck before on other cars, but never as loud as this. Called the garage where I got it from, they said bring it up (40min journey), I said I wasn’t going to drive it, didn’t know what damage was being done. Cut a long story short, picked up on low loader through BMW assist. Taken to closer BMW dealership, big stone taken out and charged £108. Fast forward a few weeks later and another stone, not as loud as the first one (had just joined here), saw this thread and thought, jees, new car with a hidden design fault, great! Was parked up at work, finished work came out, went into reverse (like suggested on here) didn’t have to it must have dropped out when stationary. Anyway, think I will have to annoy the dealership where I got it from, I aint paying over a hundred pounds each time a stone gets stuck, ridiculous!
Seen a few suggestions for do it yourself, anyone have a sure fire way that doesn’t involve taking the wheel off etc. (would do if really necessary).

The car is still under warranty till 3 years old. Don’t think I’d have paid to get the stone out, particularly as BMW Assist recovered the car. I would definitely be contacting BMW customer service as there is lots of supporting information available to confirm this is not a one off incident that’s unique to you.

This has happened 3 times to me. Each time I’ve been lucky the slow reverse then forward method has worked.

Jim S wrote: ↑Tue Mar 08, 2022 2:03 pm The more owners that complain the more the chance that BMW will do something about the awful front MSport brakes design and perhaps even offer a recall to fix it for all owners.
The problem is that the same design is fitted to several other BMW Series cars, ie 1, 2, 3, and 4 Series cars.