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Seized Rear Brake

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seized
4K views 6 replies 4 participants last post by  shotrock 
#1 ·
Yet again my rear brake seized on today. Foot pedal went as hard as rock and was forced to pull over.When cooled down forced back pistons, which allowed me to continue my journey. But appear to be a little reluctant to move back when I pump the rear pedal. Now little brakeing.

I have cleaned and done all the usual any ideas.


SHOTROCK :wall:
 
#2 ·
seized rear brake

Hmmm.......

Sounds familiar. One of my F650 rear master cyclinders lasted only a year before complete replacement, the internal white (piston?) bit seized in place on the upstroke. You do what you can to keep them clean, nurture them, bring them along and this is how they repay you, eh? Search for similar on this site, someone said they managed to strip and clean theirs. MK
 
#3 ·
The piston can get stuck in the white PTFE liner if the pedal is depressed down further than normal (during bleeding or when tramping hard on the pedal). If the piston is severely corroded at the base where it is exposed to road crap, it will score the liner badly and it will be scrap.

You may be able to extract the piston by either blowing some compressed air into the top of the unit or by tapping the unit down hard on a block of wood to free it from the top of the cylinder. Once the piston comes free, and it drops out of the PTFE liner, you can polish up the surface with metal polish or maybe flush the crap out with plenty of brake fluid.

When doing this, it MAY work, but you MUST check that the pedal holds with the pressure applied and does not creep down and no fluid drips out the cylinder base.

If the piston is stuck fast, you need to release the circlip that holds in the PTFE liner and set about trying to drop the whole lot out the body. This clip is usually corroded to a brown lump and trying to clean out the rusty debris may again damage the PTFE liner. By this time, a new master cylinder starts to look a cost-effective and safer option!

Your life may depend on this so don't take any chances!

Steve
 
#4 ·
seized brake

Thanks Steve, I kept my last dead one and will give that a try. Couldn't understand how someone would have got one open. MK
 
G
#6 ·
The rear brake on my Funduro overheated and seized on after about 10 miles. It was OK when it cooled down again. I figured it was a master cylinder problem, as I had cleaned the caliper recently, and the piston moved ok. I stripped the master cylinder, following GasGas's excellent instructions in the topic "Rear brake stickyness and bleeding problem finally resolved". When I came to bleed the system, no fluid was flowing into the master cylinder. The instructions say there must be some free travel in the brake pedal before the pushrod contacts the master cylinder piston. Mine had none, preventing the piston from moving all the way out, and blocking the inlet hole from the reservoir. Doh! This was why my brake seized on - there was nowhere for the fluid in the caliper to expand to when it heated up. Pushrod adjusted, brake system bled - 20 miles later the rear caliper was working properly and barely warm. Moral: check the easy things first!
 
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