What's happening to my brake discs?
Discussion
Hi, looking for some advice please.
Last year (<5k miles ago) I changed the discs and pads all round on the 550i, using parts from ECP. I now regret not using genuine parts as I'm having a problem with them. First of all there is a very light squeal at low speed (walking pace). Secondly, the rear discs aren't wearing well in my opinion:
Note that they look pitted and there is a band at the outer edge that isn't being swept properly. Both rear discs are in pretty much identical condition.
Meanwhile, the fronts look gorgeous:
As far as I remember, all the discs cam in ATE branded boxes (I chose these as I understand them to be the OEM supplier to BMW). I had less choice on the pads and believe the fronts to be Pagid, the rears Jurid. (Initially I ordered ATE pads all round but they were completely the wrong fitment.)
At this stage I'm inclined to buy some genuine rear pads from BMW and see if the discs clear up. Any advice welcome.
Last year (<5k miles ago) I changed the discs and pads all round on the 550i, using parts from ECP. I now regret not using genuine parts as I'm having a problem with them. First of all there is a very light squeal at low speed (walking pace). Secondly, the rear discs aren't wearing well in my opinion:
Note that they look pitted and there is a band at the outer edge that isn't being swept properly. Both rear discs are in pretty much identical condition.
Meanwhile, the fronts look gorgeous:
As far as I remember, all the discs cam in ATE branded boxes (I chose these as I understand them to be the OEM supplier to BMW). I had less choice on the pads and believe the fronts to be Pagid, the rears Jurid. (Initially I ordered ATE pads all round but they were completely the wrong fitment.)
At this stage I'm inclined to buy some genuine rear pads from BMW and see if the discs clear up. Any advice welcome.
TheEnd said:
I don't think it's a major problem, just that the rear brakes might be overspecced a little, and never really work hard enough to fully wear and polish like the fronts.
They do seem big for rear brakes. They're the same OD as the fronts, although the front calipers are twin piston vs the rears' singles. 
Pappagallo said:
Hi, looking for some advice please.
Last year (<5k miles ago) I changed the discs and pads all round on the 550i, using parts from ECP. I now regret not using genuine parts as I'm having a problem with them. First of all there is a very light squeal at low speed (walking pace). Secondly, the rear discs aren't wearing well in my opinion:
Note that they look pitted and there is a band at the outer edge that isn't being swept properly. Both rear discs are in pretty much identical condition.
Meanwhile, the fronts look gorgeous:
As far as I remember, all the discs cam in ATE branded boxes (I chose these as I understand them to be the OEM supplier to BMW). I had less choice on the pads and believe the fronts to be Pagid, the rears Jurid. (Initially I ordered ATE pads all round but they were completely the wrong fitment.)
At this stage I'm inclined to buy some genuine rear pads from BMW and see if the discs clear up. Any advice welcome.
Discs often ending up looking like that on the back axle. A bit of dLast year (<5k miles ago) I changed the discs and pads all round on the 550i, using parts from ECP. I now regret not using genuine parts as I'm having a problem with them. First of all there is a very light squeal at low speed (walking pace). Secondly, the rear discs aren't wearing well in my opinion:
Note that they look pitted and there is a band at the outer edge that isn't being swept properly. Both rear discs are in pretty much identical condition.
Meanwhile, the fronts look gorgeous:
As far as I remember, all the discs cam in ATE branded boxes (I chose these as I understand them to be the OEM supplier to BMW). I had less choice on the pads and believe the fronts to be Pagid, the rears Jurid. (Initially I ordered ATE pads all round but they were completely the wrong fitment.)
At this stage I'm inclined to buy some genuine rear pads from BMW and see if the discs clear up. Any advice welcome.
head driving with some very heavy braking should clean them off.dme123 said:
Discs often ending up looking like that on the back axle. A bit of dhead driving with some very heavy braking should clean them off.
head driving with some very heavy braking should clean them off.Accelebrate said:
I had a similar issue with genuine pads and discs. I'd greased the caliper where it contacts the pads, but I forgot the guides where the pads move back and forwards. Resulted in a bigger unswept area than you've got.
Come to think of it, the previous (original I think) rear discs were pretty corroded when I changed them so maybe I'm always going to have this problem. The squeal has been there since the new set of 4 discs and pads went on, and I've had everything apart since to apply some expensive red rubber Grease to the guide pins and back faces of the pads (which are rubber coated anyway) and every other conceivable surface. Didn't make any difference compared to the copper grease I'd been using.The only way I could clear the squeal was to do some serious bedding-in braking (approximately ten 60 mph down to 20 mph hard braking events in quick succession) to the point where I could smell the pads. But the squeal soon came back!
I've checked with BMW and the rear pads are only about £66 for a set which is only a bit more than I paid for the ECP set so this will definitely be the next port of call. A set of genuine front pads is £180 though!
Pappagallo said:
The only way I could clear the squeal was to do some serious bedding-in braking (approximately ten 60 mph down to 20 mph hard braking events in quick succession) to the point where I could smell the pads. But the squeal soon came back!
Squeals are caused by small amounts of movement of the pad in the caliper - effectively a high frequency rattle. Can happen because the guides are worn and the new pads don't have the build up of crud around where they contact the guides like the old ones did (the crud effectively acting as a dampener) or because the new pad is coming away slightly from the caliper pressure point. Better quality pads will have a soft material either painted or stuck on the back to act as a dampener. You can buy the pad backing as a self-adhesive sheet if they don't come with it already.Rubber grease is useless as it is water based and will evaporate with heat. High temperature (white) silicone grease is what should be used on the guide pins. Also, check to see if you have replaceable stainless steel sliders that the pads rest in - if so take these out and soak them in alloy wheel cleaner for a while and then smear them in copper grease before refitting them.
Your drastic action worked because the heat expanded the pads and made them a tighter fit in the caliper. Cooled down and they contract again.
I wouldn't go to the expense of replacing the pads again as you could put them in and still have the same problem - try some of the above solutions first.
Edited by r11co on Wednesday 19th March 18:01
When you go to BMW, ask for their "Value Line" parts. They are the same parts and even have the same part numbers as the full price stuff. The "Value Line" front discs + pads + wear sensor for my E63 650 were £320 as opposed to £600 for the same parts individually from the same dealer.
r11co said:
Squeals are caused by small amounts of movement of the pad in the caliper - effectively a high frequency rattle. Can happen because the guides are worn and the new pads don't have the build up of crud around where they contact the guides like the old ones did (the crud effectively acting as a dampener) or because the new pad is coming away slightly from the caliper pressure point. Better quality pads will have a soft material either painted or stuck on the back to act as a dampener. You can buy the pad backing as a self-adhesive sheet if they don't come with it already.
Rubber grease is useless as it is water based and will evaporate with heat. High temperature (white) silicone grease is what should be used on the guide pins. Also, check to see if you have replaceable stainless steel sliders that the pads rest in - if so take these out and soak them in alloy wheel cleaner for a while and then smear them in copper grease before refitting them.
Your drastic action worked because the heat expanded the pads and made them a tighter fit in the caliper. Cooled down and they contract again.
I wouldn't go to the expense of replacing the pads again as you could put them in and still have the same problem - try some of the above solutions first.
Hi, thanks for your input. The current pads have a rubber coating on the back, and this was supplemented with copper grease on the first fitting, then with the RR Grease on the second go. Unfortunately there isn't a replaceable stainless guide. It makes sense what you say about the thermal expansion. I guess the hope would be that the BMW pads would be a better fit in the first place.Rubber grease is useless as it is water based and will evaporate with heat. High temperature (white) silicone grease is what should be used on the guide pins. Also, check to see if you have replaceable stainless steel sliders that the pads rest in - if so take these out and soak them in alloy wheel cleaner for a while and then smear them in copper grease before refitting them.
Your drastic action worked because the heat expanded the pads and made them a tighter fit in the caliper. Cooled down and they contract again.
I wouldn't go to the expense of replacing the pads again as you could put them in and still have the same problem - try some of the above solutions first.
Do you have an opinion on the reason for state of the discs?
gf15 said:
When you go to BMW, ask for their "Value Line" parts. They are the same parts and even have the same part numbers as the full price stuff. The "Value Line" front discs + pads + wear sensor for my E63 650 were £320 as opposed to £600 for the same parts individually from the same dealer.
Cheers of this, I'll look into it.Vladimir said:
Might sound odd but try and stop using the handbrake (assuming it's auto?) - sorted a long term issue with the brakes on my 335d.
It's a manual, but I will try this in case. It's nearly always parked on the level anyway.Thanks all.
I did some work with a major pad friction material manufacturer developing new race pads years ago - not the sciency bit, just the driving. However the sciency but is amazingly complex from what I saw.
The makeup of the friction material is like a multi-faceted knife-edge balancing act. For (a crude) example, where brakes were generating too much heat, disc wear, grabbing or juddering, they would take out the tiniest bit of abrasive material and maybe add a bit of lube material, balancing dozens of other ingredients. Even with fractions of a percent adjustments, the brakes could go from grabbing to hardly working. It is so complex, so maybe your aftermarket material on the pads is having an impact via a different blend.
Does the car stand for periods of a few days or more? Do you use some of the wackier wheel cleaner products on your car, potentially encouraging bare metal rust? Looking at your rear disc pics, I'd suggest that there is a potential for a surface rust build up, and the lighter balance on the rear-end braking does not allow the disks to be gripped in the way the fronts are. Combine this with a less abrasive friction material in the pad, and your discs do not clean up.
Obviously, all of this is working hypothetically, but if you did not have the problem on oem pads, then it is one of many things that I would suspect as a possibility.
The other thing is, did you abrade the surface and drive to bed the pads in gently on fitting? They may be glazed reducing abrasive capabilities and not gripping the discs in the way you would want.
The makeup of the friction material is like a multi-faceted knife-edge balancing act. For (a crude) example, where brakes were generating too much heat, disc wear, grabbing or juddering, they would take out the tiniest bit of abrasive material and maybe add a bit of lube material, balancing dozens of other ingredients. Even with fractions of a percent adjustments, the brakes could go from grabbing to hardly working. It is so complex, so maybe your aftermarket material on the pads is having an impact via a different blend.
Does the car stand for periods of a few days or more? Do you use some of the wackier wheel cleaner products on your car, potentially encouraging bare metal rust? Looking at your rear disc pics, I'd suggest that there is a potential for a surface rust build up, and the lighter balance on the rear-end braking does not allow the disks to be gripped in the way the fronts are. Combine this with a less abrasive friction material in the pad, and your discs do not clean up.
Obviously, all of this is working hypothetically, but if you did not have the problem on oem pads, then it is one of many things that I would suspect as a possibility.
The other thing is, did you abrade the surface and drive to bed the pads in gently on fitting? They may be glazed reducing abrasive capabilities and not gripping the discs in the way you would want.
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