K11 Owners Group

RedBrickRider · Posted: Tue Dec 21, 2010 9:33 pm Post subject: Rear Brakes

Hi all, I'm new here and have a question. In August I purchased a 1993 K1100LT with 44,000 miles on it. I bought it from the original owner, and he had let it sit alot. Here's the problem... The rear brakes keep wanting to lock up. I mean on their own. The brakes work fine for one or two times, then start to lock up while I'm riding. I've replaced the brake lines with SS ones. I've removed the master cylinder and inspected it, but couldn't find anything wrong. I'm thinking it still has to be in the master cylinder. What am I missing? Sad

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Jim · Posted: Tue Dec 21, 2010 10:04 pm Post subject: rear brakes

Hi RBR,

welcome to K11OG!

I imagine someone has fiddled with the screw that adjusts the pedal height. We've had a few reports of fires caused by the rear brakes locking up.

There are two screws that have to be turned if you want to adjust the pedal height. Adjusting just the one will cause the brakes to lock up.

Other than that, I can't help. I haven't actually adjusted the rear brake on the K, nor had it adjusted. I did have the same problem with the front brake...
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Jim
1997 K1100LTSE 94,000 - still has gremlins!
1995 R100RT Classic 16,650 crashed - repaired!
1992 K75RTP 46,000

"We shall not all die, but we shall all be changed."

drikko · Posted: Wed Dec 22, 2010 12:16 am Post subject:

Hi RBR, probably a good question for the TECH section Smile

As well as the master cylinder stuff mentioned above it is well worth checking that the brake pads in the caliper are free to move easily and that the pistons can retract freely. One of the jobs for the o-ring around the piston is to pull the pad back off the disc fractionally so it doesn't touch the disc with any pressure when you are not braking.

The o-rings may well need replacing. You will notice they aren't a perfect square in cross section, they only go in one way around.
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Ted · Posted: Wed Dec 22, 2010 1:49 am Post subject:

What Drikko said, that is often the cause. There is also a very small fluid return hole in the MC that can get clogged over time with failure to flush the brake fluid that will cause the system to pressurize and the brakes lock up. There was a thread here some time ago with a similar symptoms and an obstructed return passage turned out to be the culprit - try a search for it.
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KOG#1

Flying Duck · Posted: Wed Dec 22, 2010 3:19 pm Post subject:

While you're mucking around, it's a good idea to clean the master cylinder. Crud can build up in there over time, especially if the bike sits for a while.

Remove it from the peg plate. Take out the small set screw on the side of it. Keep your thumb over the piston so it doesn't fly across the room. DAMHIK. Clean any crud off of the spring, seals and piston. Checks the seals for nicks - you probably won't find any. Clean out the bore of the master cylinder with some 0000 grade steel wool. Reassemble.

As Jim pointed out, have some play in the rear brake. Otherwise the piston gets pushed in too far and sticks on the set screw. Besides, it's nice to be able to activate the brake light without actually braking. Handy for when you're being tailgated or are engine braking.
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Ted · Posted: Wed Dec 22, 2010 3:25 pm Post subject:

I searched for it, turns out it was the MOA forum. From Don Eilenberger:

With the cap off the master-cylinder, and with a towel over your tank/fairing protecting the paint - cylinder level so the fluid doesn't slop out - try this test:

Squeeze lever. Release.

Do you see a spurt of fluid in the reservoir?

It's very obvious when it's there. If not - your master cylinder isn't fully returning to rest position - which blocks off the vent hole (which allows the system to relieve pressure in the lines going to the calipers) and you'll have the behavior you mentioned.
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Ted

KOG#1

SugarHillCTD · Posted: Wed Dec 22, 2010 4:52 pm Post subject:

Hey,

Welcome.

A second recommendation on what Ted stated.

Also, to add to what Ted indicated- BMWMOA is a good resource. There are differing opinions on joining MOA but I think it has its benefits- especially Don E, Paul Glaves and other K bike experts.

Best of luck with your brick.

John
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'92 K100RS4V Pearl White SOLD
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552255 · Posted: Wed Dec 22, 2010 7:57 pm Post subject:

Rear caliper could be sticky...i took mine apart, cleaned thoroughly, etc. Ensure the pistons go in/out easily, carefully inspect rubber rings...they damage easily when pushing piston back in...
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1997 K1100LT-SE
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"Black & Silver Duo"
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RedBrickRider · Posted: Wed Dec 22, 2010 8:07 pm Post subject:

Thanks Ted, and everyone else that replied. I had already checked the caliper, and replaced the brake pads. I also replaced the brake lines with SS ones. I believe the problem is in the Master Cylinder. I'm going to take it apart again and check for blockage. If all else fails, I'll purchase a new Master Cylinder.
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Lifes too short to ride an ugly Motorcycle

RedBrickRider · Posted: Wed Dec 22, 2010 8:09 pm Post subject:

PS I've been a member of the BMWMOA for 4 years...
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Lifes too short to ride an ugly Motorcycle