Rear Brake is Hot (really hot)

[sgtboring]

Checking the tire pressure my rear brake (disk) burnt my wrist. Is it supposed to get that hot? I keep expecting rim to melt and the Tire and Bags to burst inot flame. (but I worry alot).

:type

[sgborgstrom]

How much riding had you done before checking the tire pressure? Brake pads convert your forward movement into heat as a part of their natural function. Are they dragging on the disk? (My guess is they are) Is the disk discolored or scored?

The piston may be stuck and causing the pads to drag instead of retracting away from the disk after each use. There is a seal to keep grunge from building up and causing this problem but so much crap gets thrown up there it doesn't always work. The condition is exacerbated by the fact that there is really very little movement of the piston when you hit the pedal.

Just out of curiosity, why were you check tire pressures hot?

Steve

[sgtboring]

I ride a lot and I had a nail in my new! Metzler z-4 rear tire. I plugged it and have been obsessed with the tire pressure ever since. How can I tell if the brakes are compressed? When I pull the clutch the bike does not slow down.

Its not discolored that I can tell and I do not see any scoring. There are groves on the surface however . I would guess that i only use my back brake for about 20% of the work and the rest is on the front.

[Screamineagle]

I'm sure the answer is no but I must ask, did you happen to be riding with your foot resting on the brake pedal. If that answer is no, then you may have a puck sticking in the caliper. Even if the bike seems to coast well it could be stuck, that causes great friction and heat. What bike are you riding.

[sgborgstrom]

The easiest thing is pop the bike up on it's center stand and try spinning the rear wheel. You should be able to get a feel for whether or not the brake is dragging.

Leaving ones foot on the brake lever had not occured to me. I like it as the cause, simple and cheap to fix!

Steve

[saab93driver]

I've seen the rear disc get that hot after coming off of a high speed freeway ride on my R1150RS and stopping for gas at an exit. I'm sure that I don't "ride" the pedal. As a test I coasted to a stop on a deserted road from about 80 mph and the rear disc was cool to the touch so I ruled out dragging of the brake.

I rarely use the rear brake pedal and since the front lever actuates the rear too I think the system is overly biased to rear since it wears out the rear pads first. (My old R1100RS was easy on rear pads)

I can't say that it is normal, other than my bike does it too.

[ssls6]

Check your caliper sliders. They are the two rods that allow the caliper to float. I bet they need cleaning and a dab of caliper grease. Also look to see if your pads are wearing evenly. I bet one side is more worn than the other.

[RiverRat280]

Probally fine, after use they get real hot but just to check put it on the center stand and spin the rear. The pad always makes contact with the rotor but it should spin freely. If it sticks then you need to pull the caliper off and clean the pins and pistons. Its a good idea to lube the pins anyway since they'll wear out and if that happens BMW makes you buy a whole new caliper instead of just the pins.

[shoeman]

Get an infrared temp gun like a Raytek. You can get them pretty cheap now ($30-40). Carry it with you and check the disk temperature at various stops, with and without hard braking. Also check that of a friends bike when he or she rides with you. Compare the two. Only if you see abig difference be concerned. Also look at your brake fluid on your rear brake. Is it black from being burnt? If your brakes are running excessively hot it will cook the fluid. Even DOT4, which has a higher max temperature.

[j-budimlya]

Remove your rear caliper.....takes less than 2 minutes....just two bolts...

and look at the rear pads.....if one side is significantly more warn than the other....chances are that the pad on one side is dragging.....

this was happening on mine and a careful cleaning and greasing with new pads has solved the problem....

BTW, if the pads are releasing as designed, the pad wear will be pretty even....from my experience...

[saab93driver]

Checked my pads, they are pretty close in thickness within .75 mm of each other. What pins need to be lubricated? The retaining pin you have to drive out or are there other pins? The BMW manual is pretty sparse on the procedure.

[j-budimlya]

Checked my pads, they are pretty close in thickness within .75 mm of each other. What pins need to be lubricated? The retaining pin you have to drive out or are there other pins? The BMW manual is pretty sparse on the procedure.

http://advwisdom.hogranch.com/Wisdom/BFDRear2.1.1.pdf

jAll your questions should be answered there....and with many pictures....

[saab93driver]

http://advwisdom.hogranch.com/Wisdom/BFDRear2.1.1.pdf

jAll your questions should be answered there....and with many pictures....

Thanks, the carrier assembly looked easy enough to pull apart but having a guide is helpful due to all the little parts which, if damaged on dissassembly, can ruin an entire weekend. As everything is working ok up to now this looks like a project for another weekend with worse weather.

[ssls6]

Checked my pads, they are pretty close in thickness within .75 mm of each other. What pins need to be lubricated? The retaining pin you have to drive out or are there other pins? The BMW manual is pretty sparse on the procedure.

The caliper is a two piece design. The "mount" bolts to your final drive housing and has two "slider pins" that the caliper slides on. Once you have the caliper off, grab the mount and pull it off of the caliper. Wipe the pins clean, add new grease, and push the caliper back on. It's really easy.

[j-budimlya]

BTW, with even wear on the rear pads....my guess is that you are either using the rear more than you think you are...or you are dragging the rear with your "little toe" while you ride....

[saab93driver]

BTW, with even wear on the rear pads....my guess is that you are either using the rear more than you think you are...or you are dragging the rear with your "little toe" while you ride....

Anything is possible but I hardly (almost never) use the rear pedal since the front lever acutates the rear on the 1150RS. Actually, I've hardly used the rear pedal on any of my bikes over the years as that is the way I learned. I never had to put rear pads on any bike until the R1150RS (including my R1100RS).

The only time I have noticed the hot rear disc is when coming off of high speed run, even the fronts are warm which given what the brakes do should be normal to some extent, but I have not checked each an every time either. Short of me inadvertently putting my foot on the pedal, which I will consciously monitor from now on, I think the brake linking is too rear biased on the servo system.

[saab93driver]

Tested this on my bike today, '02 R1150RS, on 20 mile straight stretch, 70-80 mph no brake applications during the stretch, coasted to a complete stop, front and rear discs were at ambient temp as would be expected. Re ran same stretch this time stopped in a normal fashion using the brakes, front lever only, front discs a little warm, rear disc hot - too hot to touch and hold.

The single rear disc is smaller and out of the air stream compared to the fronts. Brakes will get hot if they are working so unless there is a problem with the linking proportion on my bike I would have assume this is normal operation of the system.

[billfiler]

Once when my brother and I were out on our mountain bikes, he fell after coming down a steep but not long hill. As the bike flipped over, the rear disk came to rest on his thigh and burned a "tattoo" of the disk into his thigh. He still has it to this day. He of course thinks it's cool. My point being that the hill wasn't that long so if you were out riding and had been recently applying the brake I don't think it's a problem.

Bill

[saab93driver]

When I bought my Trek bicycle I wanted disc brakes, mostly because I always thought they were cool on a bicycle (going back to my youth and the Schwinn Lemon Peeler I never got to have). The shop owner told me about mountain bike guys who were melting the tires on the rim type caliper brakes before they started to adapt small motorcycle disc brakes to bicycles - now that is hot...