Cracks do occur on disks that are not skimmed also. what is your point? if the disks are worn they are worn and cracks will occur eventually if you do not change them. if you still have enough thickness on your disk, they will not crack and I stand to be corrected if I'm wrong. Show me one case where a skimmed disk with thickness still over the safety limit and manufacture spec, that has cracked after skimming after the heat cycles. No jokes, just facts
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Read the WELCOME ALL BMWFANATICS post.
technical F90 Brake shudder @ hi speeds
- Thread starter Ash_Jhb
- Start date
Even BMW dealerships skim disks and no one has ever come here crying. Again, if you still have enough thickness on the disk, why throw them away? skimming has nothing to do with cheaping out on breaks. I hear some people say it compromises safety, how? when your disks are still over the safety limit in terms of thickness? then you might as well replace your disks every time you do oil change because they get thinner and thinner as you drive the car in any case. we have a perfect example here on the forum where on an LCI F30 330d, disks were skimmed at a dealership. The car was for sale not long ago. Just because people have opinions about things doesn't make them gospel hey!Go ahead and skim disks. Then come crying here when after a month they shuddering again
In the grand scheme of things, disks are not expensive. Why cheap out on a premium car? These are components that are there to keep you save when you need it the most. Cheaping out on stuff like brakes and tyres frankly blows my mind.
r0ckf1re
Well-known member
Try JSNHi V, I tried. They are refusing....they say it’s within specs.
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Ash_Jhb
Active member
Thanks Peter.
It does seem like some logic applied here.
I agree on the agents ignorance...in most places....perhaps these things are getting more complicated for them coupled with other parameters.
Anyway when you suggest to get a proper disc set-up ...is it a setup as you say....or involves getting new discs from these guys as well?
Happy to look into a set up process later without getting new components...But I need BMW to have a go at this first for obvious reasons. At least now I know what to tell them to do. Hopefully they can fix the issue.
Thanks.
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TurboLlew
Honorary ///Member
The problem is not skimming ANY discs. The problem is skimming discs that are slotted, dimple drilled, perforated or a combination. There are other factors that come into play. having 4 or 6 pads per rotor, the clamping force, the weight and heat dissipation it is expected to endure. The way these are used is different to what you would find in maybe some diesel repmobile that sits in traffic or does a few km/h over the speed limit once in a while. You won't have a problem but when you are like OP in a 460kw+ 2 tonne AWD car that accelerates RAPIDLY and decelerates from 200km/h regularly then you can see how it might make sense to take as few risks as possible when it comes to this scenario.
Ash_Jhb
Active member
Hi TurbowLlew.
I agree that I won’t be skimming my discs anytime soon.
Also agreed that the road force balancing is not the way to go. In my logic (like BMW says it takes many factors into consideration including the tyres...so if I then put in new tyres does it mean I have to redo the BF balancing again at another 3k...does not make sense to me. ?
I will definitely take it to another dealer, perhaps JSN ( I did hear some good things from me...and they are not far from
Midrand)
Thanks.
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@TurboLlew, your explanation makes sense, other guys here are very opinionated about things without any explanation to back up their story.
Ash_Jhb
Active member
This was bought over by Auto Alpina if I’m not mistaken. I’m not sure who is there any longer.
Would have trusted them if Sanjay was still there. Not sure any longer.
Thanks. Will keep them in mind though.
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@Ash_Jhb
I wont get tangled into the discussion of skimming or not, in my "non qualified diagnosis" based on your explanation of the symptoms its is clear that one or more of the discs are warped slightly causing them to run out of true. This is called run out and is check for with a pin type dial gauge. So while your discs may be within manufacturers thickness and not requiring a change this can still be an issue.
The "tech" meaning appie needs to do a run out test on your car and check for warping on the rotating parts and replace accordingly. i am posting two links below to share more information. The second link is from a bike site but they have a graphic that clearly indicates how a disc out of true wobbles.
www.parktool.com
Some side information on why this happens, braking from high speeds or long sustained braking causes exceptional heat build up, typically if you kept moving the air would move that heat away and all will be good, however if you came to a rapid stop and remained stationery while keeping pressure on the brake pedal then all that heat has nowhere to go and essentially creates a hot spot on the area that is clamped on the disc. Stopping a big luxobarge creates a large amount of heat energy that has to go somewhere.
good luck!
I wont get tangled into the discussion of skimming or not, in my "non qualified diagnosis" based on your explanation of the symptoms its is clear that one or more of the discs are warped slightly causing them to run out of true. This is called run out and is check for with a pin type dial gauge. So while your discs may be within manufacturers thickness and not requiring a change this can still be an issue.
The "tech" meaning appie needs to do a run out test on your car and check for warping on the rotating parts and replace accordingly. i am posting two links below to share more information. The second link is from a bike site but they have a graphic that clearly indicates how a disc out of true wobbles.
Disc Brake Rotor Truing
This article will outline the diagnosis and repair of a bent or warped rotor, both when using common hand tools and using a rotor truing gauge such as the DT-3.
www.parktool.com
Some side information on why this happens, braking from high speeds or long sustained braking causes exceptional heat build up, typically if you kept moving the air would move that heat away and all will be good, however if you came to a rapid stop and remained stationery while keeping pressure on the brake pedal then all that heat has nowhere to go and essentially creates a hot spot on the area that is clamped on the disc. Stopping a big luxobarge creates a large amount of heat energy that has to go somewhere.
good luck!
ChrisPy
Active member
My 2c. I’m by no means an expert so feel free to argue with me.
If you have done heavy braking and then parked your car you could have “overheated” your brake disk and then allowed it to cool unevenly. Basically this is because the area of the disk exposed to the air will cool down quicker than the area under the Caliper. This will also not necessarily mean that your disk would be warped. What you have actually done is changed the material properties of the disk you will have a area of disk that is now harder (or softer I can’t remember which) that will wear at a different rate to the rest of the disk and will over time start to shudder which people will incorrectly label as warped.
What you might have now is a disk with differing material properties. In cold or warm state it’s the same thickness all round and this doesn’t vibrate under braking. However at higher speeds the heat you are putting into the disk is passing a threshold that the disks expand uniformly (due to a section of it being hardened) and in turn starts to vibrate. (That is why skimming wouldn’t help in this case but that dead horse has already been flogged)
I would go to another dealership and take them for a ride if they would allow it, or alternatively wait until your disk starts vibrating under 140kph which I would say is inevitable although that might take some time, and then get the disks replaced. IF they agreed to it.
When you do get your new disks, keep in mind that you should let some Air get over them before parking the car. Also that it’s not only a single hard braking instance that could do this, but rather repetitive braking. Most of this happens when gunning it from Traffic light to Traffic light. Because your not getting a long stretch of road where air over the brakes can cool them down and are sitting on the brake pedal at the traffic light immediately after a hard brake input.
So looking into your driving behaviour to see how you could prevent the above (if that is what is wrong with your brakes). When pushing between traffic lights I generally get off the throttle early and brake a while before the next light and then free wheel the last bit then brake. Then try get off the brakes as quickly as I can if possible. If I do lots of this then I make sure I do a long stretch with light to minimal braking before I park it to ensure that they are in a “cool” state when parked.
If you have done heavy braking and then parked your car you could have “overheated” your brake disk and then allowed it to cool unevenly. Basically this is because the area of the disk exposed to the air will cool down quicker than the area under the Caliper. This will also not necessarily mean that your disk would be warped. What you have actually done is changed the material properties of the disk you will have a area of disk that is now harder (or softer I can’t remember which) that will wear at a different rate to the rest of the disk and will over time start to shudder which people will incorrectly label as warped.
What you might have now is a disk with differing material properties. In cold or warm state it’s the same thickness all round and this doesn’t vibrate under braking. However at higher speeds the heat you are putting into the disk is passing a threshold that the disks expand uniformly (due to a section of it being hardened) and in turn starts to vibrate. (That is why skimming wouldn’t help in this case but that dead horse has already been flogged)
I would go to another dealership and take them for a ride if they would allow it, or alternatively wait until your disk starts vibrating under 140kph which I would say is inevitable although that might take some time, and then get the disks replaced. IF they agreed to it.
When you do get your new disks, keep in mind that you should let some Air get over them before parking the car. Also that it’s not only a single hard braking instance that could do this, but rather repetitive braking. Most of this happens when gunning it from Traffic light to Traffic light. Because your not getting a long stretch of road where air over the brakes can cool them down and are sitting on the brake pedal at the traffic light immediately after a hard brake input.
So looking into your driving behaviour to see how you could prevent the above (if that is what is wrong with your brakes). When pushing between traffic lights I generally get off the throttle early and brake a while before the next light and then free wheel the last bit then brake. Then try get off the brakes as quickly as I can if possible. If I do lots of this then I make sure I do a long stretch with light to minimal braking before I park it to ensure that they are in a “cool” state when parked.
Kyle
///Member
A friend experienced a similar issue with his F80 CP. According to the dealership, BMW SA instructed them to remove, clean and refit the brakes (which obviously makes so sense) after which they submitted a report that the issue was obviously not resolved. Seems like this is their equivalent of "have you tried restarting your PC?".
What made the matter worse was that the brakes became incredibly noisy after the second round of "cleaning" and we were told that it's normal 😂...
Long story short, dealership refused to replace the pads and BMW SA didn't care, so he ended up trading the car in.
What made the matter worse was that the brakes became incredibly noisy after the second round of "cleaning" and we were told that it's normal 😂...
Long story short, dealership refused to replace the pads and BMW SA didn't care, so he ended up trading the car in.
rsgordini
Active member
Take it to another dealer until the discs and pads get replaced. It happens on many sports cars that the discs get warped from high speed and bad cooling. Not sure if you bought your car new or demo or used but either way this could have been caused by a bad test drive or even by you slamming on brakes a few times from high speed. I warped the discs on my m140i when it was still new. Luckily it wasn’t bad and I lived with it. But I learnt for my next car what not to do.
Worse case scenario you wait till they need replacing or pay out of pocket for new brakes. Which won’t be cheap.
Good luck let us know what happens
Worse case scenario you wait till they need replacing or pay out of pocket for new brakes. Which won’t be cheap.
Good luck let us know what happens
Ash_Jhb
Active member
Could be....because of the cars acceleration , it gets to hi speeds very quickly and then the brakes come into action even quicker. With that said it’s machine and BMW should be able to address issues like this... these issues will annoy many enthusiasts and may find themselves moving to the like of Porsche etc.
Anyway can’t blame anyone...I have it from brand new (18months now). I will continue to go back to BMW to get it sorted. Now that I have a few ideas (thanks to guys here) I can “educate” them on what they should be looking at.
Cheers.
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Ash_Jhb
Active member
Hey Guys. UPDATE
Finally got ABM to replace the discs and pads. They only did the front ones though.
However not without vigorous persuasion, and despite the little run around….but just kept focus…
I must say it really does help when you have friends in the game.
Anyway Still running them in now…150kms done. 350 to go. Will keep updated. Really keen to see the outcome.
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Finally got ABM to replace the discs and pads. They only did the front ones though.
However not without vigorous persuasion, and despite the little run around….but just kept focus…
I must say it really does help when you have friends in the game.
Anyway Still running them in now…150kms done. 350 to go. Will keep updated. Really keen to see the outcome.
Sent from my iPhone using Tapatalk
Salt
///Member
1. I've had disks skimmed multiple times before and never an issue.
2. The disks that I've had skimmed were on standard disks (not drilled or slotted), not high performance cars.
3. If they are skimmed within spec, factually no issue.
4. A car under plan should get new disks under plan.
5. I would not skim high performance disks.
OP should find a dealership that will assist imo. If ABM doesn't want to, go somewhere else. EDIT: glad ABM assisted, a good dealership in my experience so pleased to hear this! Happy for the OP!
Felt I needed to give my 2c 😜
2. The disks that I've had skimmed were on standard disks (not drilled or slotted), not high performance cars.
3. If they are skimmed within spec, factually no issue.
4. A car under plan should get new disks under plan.
5. I would not skim high performance disks.
OP should find a dealership that will assist imo. If ABM doesn't want to, go somewhere else. EDIT: glad ABM assisted, a good dealership in my experience so pleased to hear this! Happy for the OP!
Felt I needed to give my 2c 😜
///M Individual
Well-known member
Glad you came right bud! Is the shudder gone completely now?
