Front calipers lock up when hot.. Thanks

[Anonymous]

I recently purchased a 1980 GS850 (33,000 miles). I think the bike sat for a while before I became the owner. I have already replaced the seals in the master cylinder to correct the spongy brake lever. The brakes do a great job now except when the front brakes get hot (i.e. sitting in the sun for about 40 min). They clamp down on the rotor hard enough that bike will almost not move. The brakes start to release after the bike sits in the shade for awhile. I reviewed some of the other brake related postings, and have found a great site explaining the caliper rebuild task. Is this what I have to do to correct the problem? Thank you for your assistance.

[argonsagas]

Before you do any other work, invest a few dollars in a spray can of brake cleaner. It MUST be brake cleaner, not any other solvent.

Put down newspapers or cloth to soak up the inevitable mess.


Spray the fluid liberally all around the calipers.

Let it dry. It is quite likely your problem will be cured.

These calipers tend to collect debris, much of it in the form of dirt or fibres from worn brake pads.

Once cleaned, repeat this at least once every riding season, and your problem will likely not return.

[Anonymous]

I appreciate the response. I just returned from trying the solvent. Unfortunately with no success.

[Anonymous]

i have had this problem . crack the bleeders one at a time and let a little fluid out that should release them might pay to bleed the system
ozman

[Anonymous]

Fluid return in the bottom of the M/C is blocked. Fluid expands when heated. Can't go back into the M/C, so it pushes the pads out instead.

[Anonymous]

I appreciate you responding to my question, although I was hoping that you might elaborate further. I pulled the M/C apart and changed all of the seals and the piston. I cleaned out the inside of it as well with solvent. However, I did notice that there were two round indentions in the top of the M/C (where the base of the reservoir sits). One was a hole into the M/S and the other did not enter the cylinder. This one appeared to only be a small round recess (it was positioned beneath a plastic tip on the bottom of the resovoir ? if I remember correctly). Would either one of these be the return that you wrote of? Could the round recess that did not extend down into the M/C actually be a hole that was plugged? Thank you for your assistance.

Fluid return in the bottom of the M/C is blocked. Fluid expands when heated. Can't go back into the M/C, so it pushes the pads out instead.

[gremlin]

remove the front caliper and clean it out. flush the brake lines, when you reinstall them make shure you lube the piviot points.

it sounds like you may have gunk in the caliper or line that keeps the fluid from going back into then resovoir.

[focus frenzy]

check the adjustment screw on the brake lever, if it is not allowing the master cylinder piston to return all the way outward to its stop it won't allow the piston to clear the reservoir port, allowing pressure to build up in the line.
with the lever all the way out there should be a small air gap between the lever adjusting screw and the master cylinder plunger.
when you had it apart did you replace the spring? this is a common problem that comes up with older bikes, the spring breaks or gets weak and can't push the piston back all the way to clear the reservoir port.

[Anonymous]

Hi all. The M/C plunger is returning all the way (stopping at the circular clip which holds it in). As far as the spring... yes, it came in the piston/cup set. I guess I am going to have to redo it what I have done and then some. Thanks.

[Anonymous]

Front brake drag

I read the posts quickly and want to say I had the same problem with 81 GS850G.... the master cyl has a very small hole that was stopped up. I ran a small drill bit by hand to clean it out. Now the fluid can flow back and allow the pads to open. NOTE: Replace the caliper piston o-rings, pads and fluid if you think they got too hot.

[Don Lobacz]

Yes, the indentation should have a small orifice going into the plunger bore. Open it up with a small wire, not a drill bit.