M40i brakes - design flaw uncovered

[Flyingfifer]

Shocking, not fit for purpose. BMW should be ashamed of it.

It looks buckled, like its been damaged and bent out of shape, I'm actually lost for words at how bad that is

[Jim S]

Shocking, not fit for purpose. BMW should be ashamed of it.

It looks buckled, like its been damaged and bent out of shape, I'm actually lost for words at how bad that is

It hasn’t been damaged or bent out of shape. That’s the way its designed - a real mess.

[TitanTim]

I would be very surprised if the shields were fitted damaged at the factory, the dealer should be able to compare to another car in stock. They probably just need fettling i.e. bending back slightly to minimise chances of any stones lodging behind the disc, not great but probably a simple fix.

What tyres are they fitting now? if Michelin PSS they throw stones up like nothing else, one of the reasons I went back to runflates from the M135i to the M140i it was just constant flying stones with the Michelins stripping the water based piss poor paint away from the sills.

The hubs look to be the same as on my M140i and rust up lovely if not protected, I find parts of BMWs quality pretty shocking at times when supposed to be a premium product

Tim.

[john-e89]

Shocking, not fit for purpose. BMW should be ashamed of it.

It looks buckled, like its been damaged and bent out of shape, I'm actually lost for words at how bad that is

It hasn’t been damaged or bent out of shape. That’s the way its designed - a real mess.

I’m guessing it’s to direct some cool air flow to the disc much like a duct if the cars been used hard, needs a top lip as suggested doesn’t it.

[Jim S]

It looks buckled, like its been damaged and bent out of shape, I'm actually lost for words at how bad that is

It hasn’t been damaged or bent out of shape. That’s the way its designed - a real mess.

I’m guessing it’s to direct some cool air flow to the disc much like a duct if the cars been used hard, needs a top lip as suggested doesn’t it.

You are correct in what you say, the design is that way to allow air to flow straight from the front bumper air vents across the brake discs. No thought put into the design to prevent stones from falling into the brakes.
I got the opportunity at my dealer the other day to inspect the brakes when the car was on the ramp with all the wheels off. That's when I took the photos I posted. I have to say that the quality of all the brake components are top drawer and very substantial. Even the shields are sturdy galvanised steel. Just a pity that the design does not have them bending over at the top to prevent the stones falling straight into the gap. On the front, there is an added problem where the shield folds in at the bottom closing the gap and trapping the stones that fall through to the bottom of the rotor. Not a very smart design at all.

[Toejedi]

I’ve had the same issue happen to me a couple of days ago.

I went a little wide on a corner and ran over a pile of loose gravel that had accumulated by the edge of the kerb, I was only doing 10-15 mph and I was applying the brakes at the time to stop at a roundabout.

Horrible screeching noise, I knew exactly what it was. I simply pulled into a quiet side street and went forwards and back a couple of times (10mph) each time jamming the brakes on. On the 2nd attempt it dislodged the stone.

It’s the first time it’s happened to me (1,600 miles and 2 months of ownership), so I’m unsure if it’s a one-off or this design issue.

I’m happy to help submit something to BMW if it helps.

My previous 3 z’s never had this problem. I suppose a true test would be finding a road that’s been recently relaid with those loose stones they throw on!

Contact me if you want any further info.

[Jim S]

I’ve had the same issue happen to me a couple of days ago.

I went a little wide on a corner and ran over a pile of loose gravel that had accumulated by the edge of the kerb, I was only doing 10-15 mph and I was applying the brakes at the time to stop at a roundabout.

Horrible screeching noise, I knew exactly what it was. I simply pulled into a quiet side street and went forwards and back a couple of times (10mph) each time jamming the brakes on. On the 2nd attempt it dislodged the stone.

It’s the first time it’s happened to me (1,600 miles and 2 months of ownership), so I’m unsure if it’s a one-off or this design issue.

I’m happy to help submit something to BMW if it helps.

My previous 3 z’s never had this problem. I suppose a true test would be finding a road that’s been recently relaid with those loose stones they throw on!

Contact me if you want any further info.

Sorry to hear that Toejedi, but I am not surprised. You only have to read through the contents of this thread to understand the problem and what needs to be done by BMW to properly fix it.

It would be helpful if you could report this to your dealer and ask them to add it to the "BMW HQ Technical Case" that my dealer has opened on my behalf. If every G29 owner that has this problem does that, BMW may be forced to redesign the brake shields and retrofit them. We can but hope.

Thanks for taking the time to provide your comments. Happy motoring. I hope you are enjoying your car in spite of this problem, just like I am.

[Flyingfifer]

Shocking, not fit for purpose. BMW should be ashamed of it.

It looks buckled, like its been damaged and bent out of shape, I'm actually lost for words at how bad that is

To clarify, I know the shield isn't actually buckled, its just how it appears when you first see it lol

I’m guessing it’s to direct some cool air flow to the disc much like a duct if the cars been used hard, needs a top lip as suggested doesn’t it.

To be fair that does make perfect sense its certainly a far more airflow positive design vs a semi enclosed shield

[flybobbie]

I notice the water channels on the Goodyear asymmetric 3 tyres or wider than the 2's.

[Jim S]

Update on the stones in M Sport brakes problem on the Z4 G29.

My dealer tells me that following the report and video that he sent over to BMW AG for review. Their response is that it is unlikely that the design of the shields will be carried out as they have not received sufficient complaints from owners to justify this.

I am very disappointed with this response to the extent that I am extremely unlikely to purchase any more BMW's in the future, having already purchased 8 brand new expensive and fully loaded models, 7 since 2005.

[ronk]

Update on the stones in M Sport brakes problem on the Z4 G29.

My dealer tells me that following the report and video that he sent over to BMW AG for review. Their response is that it is unlikely that the design of the shields will be carried out as they have not received sufficient complaints from owners to justify this.

I am very disappointed with this response to the extent that I am extremely unlikely to purchase any more BMW's in the future, having already purchased 8 brand new expensive and fully loaded models, 7 since 2005.

They need to wake up !

I took an M40i out on test and the stone jam happened to me - it certainly coloured my wife’s opinion of the car!
The dealer wasn’t concerned when I took the car back in - they said that they would check it!

[ronk]

This photo of the front M Sport brake assembly clearly shows what the problem is. The wide open top is a magnet for catching stones and the bottom of the shield bends in towards the disc closing the gap and trapping the stone. The bottom of the shield can't be bent outwards because of the track rod end which is right up against the shield.
image.jpeg

That is silly design - it’s as if they wanted to catch stones.
If the bend towards the disc cannot be moved, could they at least remove the cup with a pair of tin snips?

[john-e89]

I feel for you Jim but I’d think you have absolutely zero chance of changing anything. It’s clearly a design flaw but getting them to even acknowledge a problem will be head against a brick wall. You’ll get fluffed off with any old guff, nothing will change unless it becomes a problem for the vast majority of owners.

[ronk]

Tin Snips!
At least it would take away that bonkers inward curl.

[Jim S]

My dealer also told me that BMW say that they cannot prevent stones getting into the brakes. Fair enough, but I say that the design should let the stones pass through and not trap them due to the inadequate design of the shields. :

The good news is that I have had no further occurrences since the last event, but I have only done about 500 miles since then as I am reluctant to take the car too far in case it happens again. I have now purchased and keep in my boot a scissor jack and extending wheel brace plus a camping mat to lie on if I have to get under the car to get another stone out.

Interestingly, the exact same M Sport brakes design has been incorporated into the new G20 3-Series, so let's wait and see how many owners of these cars have the same problem. Only time will tell.