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R1100RT rear brake issues


Trebor

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Well, the other day, I noticed quite a bit of brake dust on the rear wheel. Had a look at the pads, seemed like they would last a little while longer. But they didn't. Today I met with a little hot "metal on metal" action, resulting in a little damage to the rotor. So here's my list of questions...

 

  • What is the conventional wisdom on turning BMW brake rotors? Are there cheaper alternative sources for this part?
  • I bought this bike used and have found that the rear brake always seemed a little "soft", however I could activate the ABS by stomping on it, so I never gave it a second thought. The bike sat for a while before I bought it and I completely flushed the brake lines, but the front master cylinder needed to be replaced (not by me). Are the soft brakes (and what appears to be a lack of disengagement from the rotor) indicative of a problem with the master cylinder? sticky caliper? old pads?
  • Is a caliper rebuild advisable nevertheless?
  • If I rebuild the caliper, will I need to bleed at the ABS unit? (Remember, this is the "old skool" R1100, not the new-fangled R1150).

 

Thanks

 

Edit: I was going over the "Oilhead maintenance" document as I thought I remembered something about this. Sure enough:

 

Warning: Due to a sticky rear brake retaining pin, the rear pads can wear out in

only a few thousand miles.

 

Well, apparently my pin got sticky because it was only the outside pad that had the issue. Please touch on the above questions if you can, I'm curious on where to go from here.

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When you replace the pads clean the caliper and especially the pins (and double check that the caliper floats properly on the pins after you reassemble) and you will probably be A-OK. If the brakes still seem soft you can bleed them to be sure you have no air in the lines (generally it isn't necessary to bleed the ABS unit but in this case you might want to just to be sure.)

 

There are aftermarket alternatives for the rear rotor from EBC and Braking. I have used the EBC part and it was well made but not a whole lot cheaper than OEM, maybe by 30 bucks or so.

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russell_bynum

Well, apparently my pin got sticky because it was only the outside pad that had the issue. Please touch on the above questions if you can, I'm curious on where to go from here.

 

Same thing happened to my RT a few years ago (except it didn't get to metal-on-metal). Now, as part of my annual service, along with bleeding/flushing the brakes, I remove that pin and clean it. Usually I'll also hit it with the wire brush and maybe even some light sandpaper if it's particularly gritty.

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BMW rear discs are soft and must be fitted with soft pads otherwise the rotor wears unevenly causing poor contact when new pads are fitted.

 

I would not recommend turning the rotor. I recommend that you thoroughly rough up the rotor with 80 grit. Go after it vigorously.

 

Pull the two halves apart and lube the pins. I use a lithium moly grease. Insure that you don't get any grease on the rotor....moly will embed in the metal and cause ongoing loss of friction. Clean your caliper thoroughly....use a spray solvent then be sure the metal anti-squeal clip and tail clip are not bent and are in good condition. Press the pistons back into their bores, expressing the DOT4 from the caliper and reassemble the caliper and reinstall.

 

Bleed thoroughly and break in the new pads with moderate rear brake use for the next 50 miles or so.

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Visited the local BMW experts today, and gave me a quote that I might have expected. BMW does not endorse turning of their rotors and suggested their replacement. I'm tempted to let them do it even though it's an excessive expense. They also suggested that I wouldn't be able to get the loctited nut off the rear tire without a torch. Hrmpf.

 

thanks for the counsel.

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They also suggested that I wouldn't be able to get the loctited nut off the rear tire without a torch.
Well a torch is a bit extreme, but it might take a bit of heat from a heat gun to soften the loctite a bit.

 

ISFA turning the rotors, I suspect the real challenge would be finding someone who could jig up the weird inside shape.

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russell_bynum

Well a torch is a bit extreme, but it might take a bit of heat from a heat gun to soften the loctite a bit.

 

A heat gun works just fine for that.

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I agree with DEF about lubing the caliper pins. They make special stuff for it; mine looks like mint jelly. I just noticed that my outboard pad is wearing quicker than inboard so I'll address this as things get back together.

 

I also concur about roughing up the disk with some sandpaper or gently with emory cloth so long as it meets thickness specs afterward. Crocus cloth is too fine.

 

I can't remember any loctited bolts if you just want to take your wheel off. They don't come up until you need your differential removed. I sure wouldn't use a torch on that alloy; heat gun or blow drier will do.

 

 

Bob

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Well, the thought of being without my ride got the best of me, so I bought a new di$k and removed the bike's hind foot. No problems with loctite until I tried to remove the ABS sensor ring from the old disk. Those things are stuck -- and they're soft 3mm hex screws. Guess I'll try to drill them out before I go back for a new ring. Thanks for the comments.

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Finished the whole operation (replace, no caliper rebuild) and had some time to ride on it. A couple of notes: The disk got hot enough to melt the gaiter on the rear drive a little bit: something to keep an eye on. Also, the rear wheel spins, but with some friction. I'm told this is normal, but the rear disk is getting pretty warm (compared to the front) after highway speeds. Is this something that will work itself out as the pads wear in or symptoms of the same problem?

 

thanks

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Stan Walker

If you ride a few miles then coast to a stop the rear disc should be about the same temperature as the final drive, warm, not hot. If it's hot, something is wrong.

 

Stan

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No problems with loctite until I tried to remove the ABS sensor ring from the old disk. Those things are stuck
Am I going to have this problem with my 1150RT front ABS ring? I have a new rotor to put on but hadn't anticipated this kind of problem, don't want to start the job before I leave this week if it is going to be a pain.
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Stan Walker

Am I going to have this problem with my 1150RT front ABS ring?

 

I don't recall any problem when I replaced my front rim on the '02 RT (bent it on an Xmas tree). But I may have used my hot air gun (don't remember).

 

Stan

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Melting of the rear drive gator is highly abnormal. Check your work carefully before further riding. Something is wrong back there.

 

Start with the DOT4 reservoir...make sure it is not too full.

 

Those of you having trouble loosening the Loctite, use a small hand torch as I suggested previously. You cannot get enough heat into the material to free the Loctite's grip using a hair dryer. A hand torch is fine but, do not dwell on the part for long periods.

 

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Am I going to have this problem with my 1150RT front ABS ring? I have a new rotor to put on but hadn't anticipated this kind of problem, don't want to start the job before I leave this week if it is going to be a pain.
The screws are kind of soft and have some plenty strong Loctite applied (in typical BMW overkill) but use sufficient heat and you shouldn't have a problem, or at least I didn't.
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The replacement screws had red loctite on them. I hit the old ones with a propane torch for a little while and that didn't make much of a difference for me. First time doing that operation, though.

 

cheers

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Melting of the rear drive gator is highly abnormal. Check your work carefully before further riding. Something is wrong back there.

 

It's really just a "cosmetic melt" that happened from when the rotor got heated up from the metal part of the old brake pad abrading away my previous disk. Those two items are a little close for comfort, IMHO. Will keep a careful eye on that area and double check the fluid level.

 

thanks for the heads up.

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