Squealing Brakes

[dwire]

Hello Manfred. Boy, the VIN's have gone a long way since my 2980123 bike! I don't seem to have it in the classic fische here, but Max BMW does, albeit not too good a description, as I can not directly tell yes no of the presence of a few things, so I guess the best I can provide would be general for any disc and caliper.

Also keep in mind, I am not sure but would not be the least bit shocked if in 1987, BMW motorcycles were still equipped with asbestos - that in of itself (changing from a soft compound like asbestos to something harder) will cause brakes to squeal. I cannot see in the fiche if there is supposed to be a shim-plate between the piston and the pads - looks like not as normally that would be built in.

Someone in the thread mentioned turning the wheel and getting a squeak or "chatter" at the same point each time around. This is most likely from the bike sitting for a short period and allowing the reaction to take place between a steel disc and semi-metallic pads. With the absence of having a good look at these calipers and the associated parts, I'd hate go into detail of all the possibilities, as that's juts a waste of space. I can say, you're unlikely to permanently cure a chattering (squeaky) brake with Perma-Goo; it comes back. When replacing pads, ask for the softest compound available - ESPECIALLY if it came with asbestos originally, some of the best substitute friction materials for asbestos have been the new organics, but there's new technology every year to try and solve problems or outperform older products. It also can be from a warped disc, but the aforementioned is actually likely more common.

Obvious mention to the run-out being excessive on the disc; BMW will have a spec for this surely it is likely very close tolerance considering the size of the disc and caliper. I also again, leading back to compound changes; especially from original asbestos to a hard semi-metallic would check the aftermarket scene and see if anyone that is producing replacements with a softer asbestos-like compound (or not for that matter) has resized the thickness of the backing portion of the pad (called the "shoe"; friction material on a pad is called the "lining") has a version with a built in shim-plate to make up for some of the chatter issues; this is what was done in the automotive industry and helped a great deal.

Beyond that, I'm not well equipped to say much. I'm disappointed the fiche is sort of lacking on that model, but judging by the pictures of the replacement pads, it seems maybe the parts are a bit lagging too - unless I missed something, they seem predisposed to chatter. One person said take them out and use them - yeah; so far that is great advice without seeing what else is available in the aftermarket for them...

Hope this helps any at all. Perhaps one of these days I'll get a good look at a pair of the modern discs and have them to inspect. This part of the World does not see a whole lot of BMW riders really (I know they're here somewhere, but I NEVER see them...)

[ME 109]

After much surmising about squealing brakes, I wonder why it is that I can produce a loud squeal from the front disc/s without touching the brake lever, and a wheel speed of about 2 rpm?

Bear in mind that I have to 'play' the wheel. The squeal will start at 'a' point of rotation and will continue as long as the same rotation speed is maintained.

It shows that the squeal can be produced under vastly different dynamics.

My RS brake squealing has stopped of late on the front, and reduced on the rear. The pads are more than two years old.
The discs won't have altered/worn in a few months to have stopped the squeal.

[richard t]

Did anyone suggest chamfering the leading edge of the pads?

I've done that for years on cars, some car brake pads come that way.

[dwire]

Hard compound -lot's-o-stuff. Your description just sounds like a hard compound combined with the notion that there are a number of forces that "retract" the pads away from the disc once they have been applied - the vast majority of brakes around will drag until you've used them, discs for slightly different reasons than drums, but I'm unsure what you are saying. You are shocked that disc brakes that ordinarily will drag due to being sandwiched right up against a disc that need vary only say 0.0001" either way could make a squeal or chatter while turning them over on an stand?

This should be totally normal... It becomes almost absurd the complexities of how such simple devices work, but as an example, what do you think when one is speaking about high performance brakes such as a race car, one does on the parade lap other than put heat in the tires and wave to fans? Ride the sh1t out of the brakes - there's good reason for this too...

After much surmising about squealing brakes, I wonder why it is that I can produce a loud squeal from the front disc/s without touching the brake lever, and a wheel speed of about 2 rpm?

Bear in mind that I have to 'play' the wheel. The squeal will start at 'a' point of rotation and will continue as long as the same rotation speed is maintained.

It shows that the squeal can be produced under vastly different dynamics.

My RS brake squealing has stopped of late on the front, and reduced on the rear. The pads are more than two years old.
The discs won't have altered/worn in a few months to have stopped the squeal.

Yes, likely not a lot, but the thing you've neglected to consider is how the pistons retract (big one) and as well heating and cooling soaks. Many cars (I'd gander say all I've EVER encountered) jacked up after sitting overnight will at minimum drag partially around and most the entire length of the rotation. Whether they squeak or not, well that is a matter of their design and such. Also keep in mind, with vehicle brakes of any kind they ALL "squeak" we used to use special digital recorders to "listen" to this squeak that was above the human hearing range on brakes operating normally. But yes, otherwise we could get them to squeak and chatter anyway a number of ways... I'm totally guessing as well, but the size and such with lower density parts (aluminum calipers rather than cast iron, or HUGE aluminum or more exotic metal) calipers could be a factor in having your brake squeal instead of rub on the stand.

I still do not know for sure which it is you are having an issue with, or truly asking; them squeaking all day on a trip, or sitting on a stand side loaded... That would make your query easier. Frankly sounds like your bearings are lose.. (kidding really; don't know how much variance they should have at proper load - ask Duane, I'm not blaming him today...)

It would seem I am the only one to ever put a cold car on a lift and have to man handle the seemingly frozen up perfectly operational disc while remove the wheel, then with making no changes but removing the wheel and recording said disc thickness drive it around the block to have it spin freely. No? Anyone?

And since this just came in below:

I've done that for years on cars, some car brake pads come that way.

Indeed; by the time I "wrapped" in that area, everything I saw pretty well came that way as well as a cheapening them up by putting only one wear sensor on them - so they could only be installed one way, which was a PITA. Also the backing/anti rattle pads were getting skimpier as well (they all used to cover the entire back.)

[ME 109]

I still do not know for sure which it is you are having an issue with

Um, squealing brakes Doug.

I can't really recall ever having my brakes squeal like they were/are, in 19 years that I've had this bike.

No, the brakes don't squeal when I'm riding along. Just when I brake. (Or playing the front wheel )

The squealing could be the result of using a different brand of pad. Metal King in this case, as opposed to EBC non sintered being the norm.

[dwire]

The squealing could be the result of using a different brand of pad. Metal King in this case, as opposed to EBC non sintered being the norm.

ME, I was not trying to insult your intelligence, nor badger you. So you have made a compound change? That surely would be suspect in my book. As well, I think you said they had been on for some time? (Correct me if I am wrong a couple years please?) it could be that both a harder compound plus their age is making them worse yet? I suppose also is it possible that your seals have swollen some in the calipers and they are not retracting quite as one would like? In that regard, while I'd guess like a vehicle with no leaks in the system, you've never added any fluid to the system, so one should be able to rule that out (not all fluids shape up the same and some can cause the seals to swell...)

With regard to the compound change; I'll leave no narrative other than I bought up a pair or two of good old deadly asbestos shoes for my bike after my near death experience with my 53 Chevy and my semi-metallic stupidity... This would be an interesting thing to see. As I can only speak "generally" ME as I don't have a BMW with front discs and all the (street) bikes I've had short experience with that did, didn't exhibit anything like that (though they very likely had asbestos on them too...)

[dwire]

Too bad you're only where perhaps I might raise you on DX via amateur radio and not take a gander at the anomaly at say Ken's rally over good food, learning and fun . [That I've yet to make it to!]

(This year, come on - this year...) I'm sure I'd ride away an enriched man in a number of ways...

I know the Max BMW fiche that showed an example of what they were selling sure looked like "tough stuff." This is 100% unscientific and not endorsed, but for anything that may have been around the asbestos era, anymore, I don't feel real comfortable if I cannot get my thumbnail into the pad to some degree. This always left me with asbestos or organics - I am sure there are new things that may be far better than the organics now, but that was the best I ever found and my old mechanic friend used to say, "Which do you want, brakes that stop and you replace a few thousand miles earlier (you're going to do it anyhow) or ones that do not?" After a front end collision, that sounded like a good advice.

[Major Softie]

The popularity of metallic and semi-metallic pads was not really related to the asbestos issue. The non-asbestos organic pads are. Metallic pads were introduced to address the complete uselessness of the organic pads when wet. I want pads that stop, but I'd like pads that stop ALL the time.

[George Ryals]

I always thought that semi metallic pads came about to speed up heat tranfer from the braking surface to the backing plate and away. I did prove on my Harley FXE that semi matallic pads were the wrong choice on ductile iron disk. They didn't stop as good as organic on the iron and they ruined the disk in short order. Stainless disks with semi metallic pads are almost as good at brakling as organic on iron and the stainless disks aren't eaten up by the semi metallic pads.

[dwire]

The popularity of metallic and semi-metallic pads was not really related to the asbestos issue. The non-asbestos organic pads are. Metallic pads were introduced to address the complete uselessness of the organic pads when wet. I want pads that stop, but I'd like pads that stop ALL the time.

From the personal side, I can say I've used quality organics in many applications with excellent results. Like most things, one size DOES NOT FIT ALL and your results may vary, but... I always use the softest compounds available and have never seen any degradation due to rain and water when used in place of asbestos materials. (Brakes designed for metallics were - DESIGNED FOR METALLICS; (I still buy the el-cheapos as unless your auto store is just providing a warranty for the same product, the lifetime pads are going to be harder and more likely to squeal, as well as ruin or eat the cr@p out of your rotor and who want to replace rotors each time with pads?) testing is all that could prove one to truly be better than another in that case under any give conditions but...

I have never seen the behavior you speak of and it is not keeping with what little I was taught and observed when spending my time in the dyno labs, as that was not my primary duty. That being said, vaporization of water in the plasma area between the disc and rotor in the case of a disc brake is what makes them become less affective - superheated steam is a new force the pads, piston(s), then transferred to the master-cylinder and in turn your brake handle/hand have to stave off to get braking while wet. This is always what was described to me by those in the know. While watching the insane tests done on these gigantic dynos that would eventually be pushed to melting portions of the disc down, or blowing up other portions of the device under test. I never felt that superheated water really cared much at that point and I don't frequently see brakes designed to run at those temps but at the race track.

I think much like a tire thread one must keep in mind what we are talking about too. Truck drums still use asbestos. F1 Racers use insanely expensive exotic carbon fiber and other materials for their binders. Our motorcycles or cars our neither, I think we could all agree on that.