brake problems

[Scudder]

I've been working on a 1980 gs850L that I picked up for next to nothin'. But, it needed extensive carb cleaning, caliper rebuilding/cleaning, etc, etc, etc. Just finished up the front brakes and put new pads on the rear. Things went together nicely, and I had no real problems with the brakes. The temperature got above 40 degrees here in Chicagoland, so I took her out for a 20 mile run. The bike ran well and had no apparent issues. When I got in my garage, I touched the front discs to make sure the caliper pistons where retracting. The discs where cool. Then I touch the back disc and it was quite hot. So, I'm thinking the pistons are not retracting, thus heating up the disc. However, I've taken the bike out on shorter runs and not had any heat on the rear disc. Could the heat be from new pads rubbing on the disc? Will things cool down when the pads wear down a bit? Or... do I need to go back in to the caliper and see what's going on? Thanks.

Scudder

[Big T]

Did you completely disassemble the rear caliper when you rebuilt it? New rubber parts?

Caliper pins good? Greased?

New brake hose?

Rebuilt MC?

If you put the bike on the centerstand, does the wheel turn freely?

[tkent02]

The return port in the MC could be clogged, preventing the brakes from releasing.
This can break your ass if neglected.

It could also be a partially blocked or internally collapsed hose blocking the fluid's return path.

[bwringer]

Other things to check would include making sure the brake pedal can pivot freely in the frame -- you may need to partially disassemble and grease this.

Your riding habits may need attention as well -- if you have the habit of resting your foot on the brake lever, you may need to change this or reposition the brake lever or peg.

[Nessism]

It's always best to tear down the brake system to clean it out. Brake fluid coagulates as it absorbs water and the only way to properly clean out a 30 year old system is to tear it down first. Also, the brake lines should be replaced. Please check the newbie mistake thread linked in my signature for more tidbits of useful advice.

[sparki]

what work did you do on the rear caliper besides changing the pads?

[Scudder]

The brakes on this bike were useless when I got it. All pistons where stuck and wouldn't move. Eventually I got the front calipers in good shape, but the rear still have a ways to go. I replaced the rear master cylinder (ceased up), brake line (totally clogged), took the calipers apart, removed the pistons and cleaned everything well. I didn't replace the rubber parts inside the caliper. Back wheel turns freely, however, being a shaft drive, it doesn't turn as freely as my chain drive GS's. I'm going to grease the pins holding the pads. They were rough, and I didn't think that that would impact the brakes too much, but thinking about it now it makes good sense. The weather today is going to be in the high 50's so I'll have a good opportunity to sort things out. Thanks.

Scudder

[Big T]

New rubber seals around the pistons

[Octain]

Yup, I recommend rebuilding the entire system. You say you "replaced" the MC but any 30 year old rubbers need to be replaced. It's easy and cheap.

[chuck hahn]

I agree with all the above and was gonna guess resting your foot on the brake lever as well. One thing that you said you DIDNT do was remove the rubber parts inside the caliper. The piston seals need to be removed and the groove they fit into needs to be claened very well and be free of that gray built up scale. The scale actually squeezes the seal excessively tight against the piston and doesnt let it float correctly. Clean that groove and replace the seals. And as suggested before..if you havent taken the brake lever out of the frame and derusted the hole and the lever then do that as well. Slop on a good coat of grease when you put the lever back thru the frame.

[Scudder]

Alright. New rubber seals it is. Once again... I guess there are not short cuts. Thanks again.

Scudder

[chuck hahn]

On 30+ year old bikes, a shortcut gets you an extended stay in the hospital...if your a lucky one. And clean the seal groove out like it looks new in there.

[chuck hahn]

And be sure the pistons are SPOTLESS..no rusty pit marks...these will lead to fluid leaks and air and moisture possibly being pulled back into the system.

[Scudder]

Thanks Chuck. I ordered the rebuild kit last night.

Scudder

[1948man]

The pins on my rear brake were pitted and a little rusted. I replaced them and greased them well and it helps a little. If your wheel spins much at all when on the centerstand, that seems about normal. Any chance you were just using your rear brake a lot right before you stopped and checked the disc temperature? You might try riding a while and making sure to not use your rear brake at all, then stop and check temp.