servo squeal

[ts2]

I can't think of a quick way of writing this, but I'll try and keep it short.

My brakes would occasionally squeal when I wasn't pressing/pulling them. The brake light would also stay on (as attested by a following rider). I took it to BMW and they said the hand guards were loose. This surprised me, as I had checked the position and it was OK, and I could also push the lever forwards and it sprung back fine.

Anyhow the problem went away for a bit. Thing is after a nice long ride the problem came back. Lever still moves fine, and hand-guards appear as tight as ever (ie moveable, but it takes some force). Forcing the handguards out of position, then back into position seems to have got rid of the problem, but it got me thinking about what the underlying problem is.

So it doesn't appear to be a crude: handguard pressing on brake lever; or I wouldn't have been able to push the lever forwards.

The lever also sprung back, so it didn't appear that the guard was gripping the lever.

My thoughts now fall to stiction. Could it be that the guard was just far enough out of place that it added friction to the lever's movement? If so, how would this cause the electronics to sense that I'm applying the brakes when I'm not? I was wondering two things, either: a) the brakes stay slightly pressed in after I brake, and so the bike doesn't realised that I'm not holding them; or b) the bike resets the "zero" position each time you put the key in the ignition, and this reset moves the brake on position to a point that is close to no brakes applied?

How does the bike sense when to start the servos? Is it a simple switch, or a pressure sensor?

So in the end I'm wondering if this has happened to anyone else and any tips on how to spot it when you're riding along?

Also I've seen Nemezis's thread on how my servo brakes will kill me if I don't change the guards [sarcasm doesn't work well in text form, but I refuse to use smilies], and I suspect these are related, but can anyone shed some light on the cause of the problem (without saying "BMW are shit, you're all going to die!"). It doesn't seem to be as simple as the guard rotates and presses the lever?


Anyhow I've written to much. Hello to anyone who made it this far in my text.

Thanks


TobyS

 

[Allan Davies]

I expect the pads could be binding and not releasing properly, our local BMW man told me this can happen to ABS/servo brakes. The solution is clean brake pads and caliper(remove all deposits from the sides and around the edges of pad with a screwdriver) , put copperslip on back of pad as per usual. Also put some on the top and bottom edges of pad (narrow ends if you follow) makng sure you don't contaminate the pads. You don't even have to take the caliper off, 5mins max I reckon. I do mine as part of my monthly once over. You'll be surprised at the amount of brake dust etc on the edges of yer pads.
HTH's
ps. I am no expert but this works for me and cured my squeal.

 

[st247]

By squealing I assume you mean you can hear the servos running without touching the brake lever or pedal? I'd check the adjustment of the front micro switch first. It may be out of adjustment enough so that a bump in the road sets the servos off. You might want to have a quick look at the rear switch aswell as they've been known to cause problems.

 

[Magwych]

Don't forget to check the rear brake pedal too. That also activates the brake light switch and hence the servo..

To asnwer one of your questions, yes, it is a simple micro switch on the front brake and back brake...

 

[ts2]

Thanks

Thanks for the replies. I've adjusted the rear brake to move the lever up a bit. I meant to do this when I first got the bike, but forgot till now. I'm not too sure how to adjust the handle bar. There is a span adjuster, but that just moves the lever. I can also see a small allen key behind the span adjuster. Is this the thing to adjust the switch position?

I'll have a play.

Also I take back any idea of the handguard squeezing the lever, as looking at it in more detail I can see no way that it'd get close. The only thing it could possibly do (before being obviously out of alignment) is press on the brake hose. As they're braided I doubt if this'd do anything.

Anyhow good to know that it is a simple switch. At least I can clean these areas if I hear it again.

Toby