M40i brakes - design flaw uncovered
- Thread starter Jim S
- Start date
Blue29 said:
Thats HORRENDOUS :thumbsdown:
Id be going mental if id shelled out all that cash for the motor and it was doing that, wonder if the Supra has the same issue? If not might be worth buying the Toyota guard, surely a straight swap!
ronk said:
Tbh spongy brakes were something I found on a recent 6 day test on an M40i, they’re certainly not as hard as an M for example but just imo a trait of the brake caliper design. I’d wager you’ll get nowhere mentioning it as the car is so new and you’re not losing fluid. Accept it for what it is perhaps, they do work very well no...?
I suppose it was only a matter of time before I fell victim too. After 14 months of ownership and 6K miles, I managed to get a stone lodged in the front near side wheel just as I arrived home last night. What a horrendous noise it made, and despite reversing and braking, I wasn't able to dislodge the stone. This morning I placed a call with BMW Assist, and when the chap arrived he took the wheel off and removed a small wedge shaped stone which had managed to jam itself good and proper. The chap also mentioned that it is now becoming a common issue The brake disc was checked, and luckily no damage was done, so all good thankfully.
The offending stone with a 5 pence coin for size comparison.
The offending stone with a 5 pence coin for size comparison.
Swiftly said:
Just curious, would BMW cover the cost if the disc/pad had been damaged?
Swiftly said:
That’s the thing that would really burst me, it’s an obvious design fault, their Assist guys are seeing this as a more regular call out cause so clearly indicating there’s an issue.
I’m interested in this topic because I can see a M40i on the horizon at some point and having this hanging there knowing BMW will likely class it as wear and tear isn’t filling me with joy.
I wonder how many cases they’ll need to retrofit a better stone guard FOC
Here’s a photo of the front M Sport brake disc assembly on my M40i, which clearly shows why there is a problem. This is the photo that I took when the car was on the ramp at my local dealer for inspection. :thumbsdown:
It has happened to me five times now and it sounds absolutely horrendous. As you drive forward the stone gets pushed further and further down into the gap between the brake disc and shield and there is no way you can get it out without removing the wheel. Even with the wheel off it is very difficult to remove the stone. :thumbsdown:
I have reported the problem to my local BMW dealer, who took photos and video and passed them on to the BMW UK Technical Department who in turn passed it on to BMW AG in Germany, so they are all very aware of the problem but so far have chosen to do nothing about it. I also wrote a strong letter to the BMW UK MD, but all I got in response was “we are very sorry to hear that you are having a problem with your car”.
By the way, I understand that the G20 3-Series has the same M Sport brakes assembly.
It has happened to me five times now and it sounds absolutely horrendous. As you drive forward the stone gets pushed further and further down into the gap between the brake disc and shield and there is no way you can get it out without removing the wheel. Even with the wheel off it is very difficult to remove the stone. :thumbsdown:
I have reported the problem to my local BMW dealer, who took photos and video and passed them on to the BMW UK Technical Department who in turn passed it on to BMW AG in Germany, so they are all very aware of the problem but so far have chosen to do nothing about it. I also wrote a strong letter to the BMW UK MD, but all I got in response was “we are very sorry to hear that you are having a problem with your car”.
By the way, I understand that the G20 3-Series has the same M Sport brakes assembly.
Jim S said: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.
Has your local dealer or BMW not offered a resolution for this yet,Jim?
Annoying that these things spoil enjoyment a bit,of a new and otherwise enjoyable car.
They must be able to make another shield that covers the top of the disc,as it should be?
Why they chose to design it that way is anybody's guess?
Jim S said: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.
Has your local dealer or BMW not offered a resolution for this yet,Jim?
Annoying that these things spoil enjoyment a bit,of a new and otherwise enjoyable car.
They must be able to make another shield that covers the top of the disc,as it should be?
Why they chose to design it that way is anybody's guess?
Unfortunately the dealer cannot offer a solution without the approval of BMW and it appears that they are not willing to do anything about it due to the high cost of retrofitting the redesigned parts to all of the affected cars. It is not only the G29 that is affected, the G20 and possibly some other models have the same set up. :thumbsdown:
I tried my very best and escalated the issue with both BMW UK and BMW AG, without success.
Shame on BMW :thumbsdown:
I tried my very best and escalated the issue with both BMW UK and BMW AG, without success.
Shame on BMW :thumbsdown:
