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Old September 22nd, 2019, 09:20 PM   #1
corksil
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Rear brake dragging.. warped caliper?

Hey, the bike sat for a while, and after a ride -- the rear brake was dragging.

The rear brake got so hot that it literally stuck and I couldn't move the bike. I pulled over, cracked the bleeder screw for brake fluid --- and it was boiling and spurting out vaporized brake fluid.

I dumped a half gallon of water on the rear brake and let it sit for a half hour til it cooled off enough to un-stick and ride home. Pretty sure I warped the rotor, it was blue from heat discoloration.

Took it all apart, cleaned everything, put it back together -- brake still dragged.

Took it apart again. Ordered a caliper rebuild kit, changed both seals on each piston, scrubbed the (small amount) of rust off with a scotch-brite, replaced the slide pins etc, put it back together.

Still dragging.

What is the chance that I got that rear brake so hot that the actual aluminum caliper casting has warped and that the piston bores are out of round?

My next step is to take it all apart again and mic the bores to see if they are round.... or save myself some time and go ahead and order a new/old ebay caliper and then rebuild everything from that point.

Has anyone gotten a rear brake caliper so hot that they warped the aluminum casting?

It was HOT -- way too hot to touch even after sitting for ten minutes.
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Old September 23rd, 2019, 12:36 AM   #2
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Old September 23rd, 2019, 06:23 AM   #3
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Quote:
Originally Posted by corksil View Post
The rear brake got so hot that it literally stuck and I couldn't move the bike. I pulled over, cracked the bleeder screw for brake fluid --- and it was boiling and spurting out vaporized brake fluid.

I dumped a half gallon of water on the rear brake and let it sit for a half hour til it cooled off enough to un-stick and ride home. Pretty sure I warped the rotor, it was blue from heat discoloration.

Took it all apart, cleaned everything, put it back together -- brake still dragged.

Took it apart again. Ordered a caliper rebuild kit, changed both seals on each piston, scrubbed the (small amount) of rust off with a scotch-brite, replaced the slide pins etc, put it back together.

Still dragging.

What is the chance that I got that rear brake so hot that the actual aluminum caliper casting has warped and that the piston bores are out of round?


Has anyone gotten a rear brake caliper so hot that they warped the aluminum casting?

It was HOT -- way too hot to touch even after sitting for ten minutes.
I don't think you could warp the caliper or caliper mount, but water on the hot rotor may not have done it any good.

You should see the caliper move when you apply and release the brake. With it apart did you make sure it was sliding easily back and forth on the pins? Did you lube them with some light high temp grease?

Seems to me that the caliper is not releasing, either do to an issue with the pins or piston - but the master cylinder could also be involved and not allowing the fluid/pressure to be released when you release the lever.

Last futzed with by jkv45; September 23rd, 2019 at 11:31 AM.
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Old September 23rd, 2019, 11:23 AM   #4
sharky nrk
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I have had problems with the rear caliper sticking on the race bike because it doesn't get used very much. Have to push pistons out most of the way, clean and lube them, and cycle everything up.

Had them dragging badly before, enough to blue the rotor up as well.
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