Rear brake rotor is smoking hot - BMW Luxury Touring Community
 
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post #1 of 7 Old Aug 19th, 2011, 5:19 pm Thread Starter
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Rear brake rotor is smoking hot

Hi, recently purchased a 99 K1200LT and notice lots of brake dust on the rear rim. After looking in to it I noticed the brake pads were almost gone. So I forked out the extra money to get factory pads and installed them. Didn't think much about it untill the new pads were dusting as well. After riding the bike, If you touch the rear rotor, it is too hot to touch it. So I havent rode it and I'm hopeing someone can help me solve the issue

Thanks
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post #2 of 7 Old Aug 20th, 2011, 6:22 am
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Re: Rear brake rotor is smoking hot

Normal

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post #3 of 7 Old Aug 20th, 2011, 7:57 am
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Re: Rear brake rotor is smoking hot

Before I dismissed the situation as normal, I'd wonder how long the brake pads lasted and how hot the rotor really is. Maybe normal, or maybe the caliper pistons are sticking a little, or there is some other underlying problem.

When you put in your new pads, having replaced the worn out old ones, did you have any trouble pushing the caliper pistons back in order to make room for the new pads? If that went smoothly you probably don't have a problem with the caliper. If you really had to wrestle one or more pistons back into their cylinders to make room for the new pads, there could be corrosion or gunk interfering with piston movement.

Were the old pads worn pretty much evenly or was one worn significantly more than the other? Some unequal wear is normal, but extremely one-sided wear would suggest a problem.

Is the brake dragging at all? Put the bike on the center stand, tranny in neutral, and rotate the rear tire by hand. Does it rotate freely or are you fighting the brake to rotate the tire?

If the above things check out okay, I'd say what you are observing is normal.
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post #4 of 7 Old Aug 20th, 2011, 8:14 am
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Re: Rear brake rotor is smoking hot

i suspect not 'normal' in this case.
depends on just how hot, but you could have really have cooked them and the rotor.
there is a gotcha! built into ABS2.

in an IABS system the wheel circuit is completely open to the air.
that is to say, worse case scenario, you service the brake system and top off the marks with fluid to 'max'. at the same time the brake pads were low but not replaced. soon after the service you replace the pads and now you have a puddle of brake fluid on the floor under the swingarm.
in order to get the new pads on and over the rotor the pucks must be completely retracted into the caliper.
therefore, any excess fluid is ejected from the system out of the vent hoses when the pads are fully separated.

however, on your ABS2, its basically a closed system. what happens when you retract the pucks into the calipers here when the fluid was at 'max' already? you try to mash the brake fluid back up the hose into the reservoir. that fluid that was taking up volume in the caliper is now pushing against the rubber boot and the air on top of it in the reservoir. the cushioning effect of the boot will allow you to get the pads installed, barely, but when the bike starts moving, and everything gets hot and expands, the pads get tighter and tighter on the rotor. the pads dragging, even slightly, can generate allot of heat.

check the fluid level before riding it.
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post #5 of 7 Old Aug 20th, 2011, 9:12 am
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Re: Rear brake rotor is smoking hot

Good and interesting input.
But, I think his bike being a 1999, would have the brake fluid pushed back into the reservoir and it would over flow onto the ground. That's what happens with my 2000.

Later model bikes with separate circuits between the brake pedal and the ABS unit and between the ABS unit and the brake caliper would behave they way you describe with back pressure captured within the system? Someone who knows the later brake systems would know, but your explanation makes sense to me. But I don't think it applies to his bike.



Quote:
Originally Posted by T25
i suspect not 'normal' in this case.
depends on just how hot, but you could have really have cooked them and the rotor.
there is a gotcha! built into ABS2.

in an IABS system the wheel circuit is completely open to the air.
that is to say, worse case scenario, you service the brake system and top off the marks with fluid to 'max'. at the same time the brake pads were low but not replaced. soon after the service you replace the pads and now you have a puddle of brake fluid on the floor under the swingarm.
in order to get the new pads on and over the rotor the pucks must be completely retracted into the caliper.
therefore, any excess fluid is ejected from the system out of the vent hoses when the pads are fully separated.

however, on your ABS2, its basically a closed system. what happens when you retract the pucks into the calipers here when the fluid was at 'max' already? you try to mash the brake fluid back up the hose into the reservoir. that fluid that was taking up volume in the caliper is now pushing against the rubber boot and the air on top of it in the reservoir. the cushioning effect of the boot will allow you to get the pads installed, barely, but when the bike starts moving, and everything gets hot and expands, the pads get tighter and tighter on the rotor. the pads dragging, even slightly, can generate allot of heat.

check the fluid level before riding it.

Last edited by CharlieVT; Aug 20th, 2011 at 1:45 pm.
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post #6 of 7 Old Aug 20th, 2011, 9:33 am
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Re: Rear brake rotor is smoking hot

Your return port in the master cylinder may be clogged with debris or corrosion. Curtis is probably on the right track but occasionally the return port will clog and the line pressure is unable to release. One of my old bikes had this happen and the pads got so hot that the metal particles in the pads welded to the rotor and it turned dark blue. To see what the return port looks like just take the cover off your front brake master cylinder and look inside. That little hole you see in the bottom is the return port and it allows the line pressure to release when the piston seal is at rest. Do NOT grab the lever hard and release it with the reservoir cap off. A stream of brake fluid will shoot out of that port and damage your paint and windshield.


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post #7 of 7 Old Aug 20th, 2011, 12:26 pm
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Re: Rear brake rotor is smoking hot

I would rebuild the caliper and clean the master cylinder thoroughly then give it all a good flush.
Be sure to clean the caliper's sliding surfaces and pins



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