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Rear brake drag even after caliper rebuild


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I've got a recurring issue that I cannot seem to figure out in regards to the rear brake seizing. Rather it is not releasing at random times. It first happened probably around a year ago. From my driveway to about 2 residential blocks away, the rear brake would not release from a stop. I tapped it with my boot several times, but I am unsure how long of a time period I waited before riding back to my house. After letting it cool down, I polished the slide pin and greased it and put it back together. Everything seemed fine.

 

Later in the summer, pretty much the identical thing happened when I was preparing to go for a spirited ride with a friend. After that last time, I haven't had an issue until about 3 weeks ago. I've probably put 3000-ish miles on it since the last time I noticed any brake drag. Three weeks ago it seized up and took me twenty minutes at least before it would release. I was tapping it with my boot; I don't know if it does anything, it just makes me feel better. This last time it had seized so hard that it ground off a good amount of brake pad. The disc is a pretty hue of blue now too.

 

So this past weekend my dad & I took the caliper off and rebuilt it and put in new pads. Put everything back together and bled the brakes. Pedal feels good and I am 100% sure that there are no air bubbles in the line. Well tonight I finally had a moment to take the bike out for a shakedown. Made it as far as the main road out of my subdivision and the brake was dragging. I thought perhaps I was just imagining it, but by the time I got a few stop lights further it was apparent that the brake was seized again. I pulled into a parking lot and just was tapping the rear brake pedal. I never got off the bike, but it seemed to release. 

 

After typing this all out, it appears that this happens on hot days and right when the bike first starts up. Each time this has happened I have cleaned the rear brake. I promise you, the rear caliper has not been this clean since it was new on the bike. 

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I forgot to mention, I found this thread and it was similar but there was no resolution:

I don't know if it is relevant, but my bike only has about 16K miles on it.

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both of my 1200's had dragging rear brakes....they never seized or felt odd through the pedal, but do leave a lot of brake dust on the wheels....i disassemble them and grease the slide pins often and it helps

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My rear started to drag.  I cleaned it up and just stopped using the rear brake... I only use it now to hold my bike at a stop at a light... or scrub speed when I see a cop...

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lshark - my pedal never felt unusual either. I thought perhaps a dirty slide pin might have been the cause originally too. However I literally poilished the darn thing then applied rgease to it. It was slicker than snot When that did not fix the issue, I bought the rebuild kit thinking perhaps the dust seals were not allowing the piston to return. But they were fine and the pistons were smooth as well. 

 

cracker - yeah, I use my rear brake a lot when I am riding a very curvy area as a trail brake. Prevents a lot of nose dive in sharp curves. I really like using the rear brake as it is intended. 

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Perhaps the internal lining of the brake hose has deteriorated allowing the fluid to apply the brake, but obstructs the "backflow."  Happens often in older cars where the outward appearance doesn't belie the delaminated inner liner.

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All the previous posts refer to working at the caliper; what about the master cylinder? If you get a little bit of dirt in the relief port in the master, this stops fluid flowing back from the line and allowing the pistons to retract. Next time your brake drags, try cracking the bleed nipple to release some pressure; if the caliper frees up, then you can be fairly sure your problem lies at the master cylinder. 

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7 hours ago, andy said:

Perhaps the internal lining of the brake hose has deteriorated allowing the fluid to apply the brake, but obstructs the "backflow."  Happens often in older cars where the outward appearance doesn't belie the delaminated inner liner.

:idea3: This would be the perfect excuse to give the boss lady to buy braided lines...

 

5 hours ago, Terry said:

All the previous posts refer to working at the caliper; what about the master cylinder? If you get a little bit of dirt in the relief port in the master, this stops fluid flowing back from the line and allowing the pistons to retract. Next time your brake drags, try cracking the bleed nipple to release some pressure; if the caliper frees up, then you can be fairly sure your problem lies at the master cylinder. 

That is an excellent idea. If it frees the caliper I have my solution and I can get the bike home without burning up the rotor.  I should probably go ahead and buy the rebuild kit. I've never done it before and it might be a good learning experience.

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Well I just returned from a brief 20 mile ride and everything seems to be OK. I removed 10ml of fluid from the rear reservoir. That took it from level with the top line to level with the bottom line. I can only assume that it was too much fluid and that was not allowing the pistons to go back into the caliper. That being said, I have no idea why it was sporadic over the past year though. 

 

On 7/15/2017 at 8:28 AM, Darrenk said:

May be time for a brake fluid flush and change...

That's pretty much what we did. All new fluid after we rebuilt the caliper. But still, it's always a good idea.

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