I removed the rear brake assy (MC,fluid reservoir, lines, caliper) a while back when i first got the bike because a bolt had backed out of the rear disc and really effed up the brakes. So now im rebuilding the back end of the bike and ive found that the pistons are locked up real good in the caliper I dont want to grab onto them with plyers or anything.. what can i do to get them un-stuck? Ive got them soaking in WD-40 right now..

Try and blow them out with compressed air.

My dinky little air compressor didnt have the balls to do it.

I ended up reassembling the brakes, putting in new fluid and pumping them out.

keithcar wrote:My dinky little air compressor didnt have the balls to do it.

I ended up reassembling the brakes, putting in new fluid and pumping them out.

thats exactly what i had to do with my 125,there was no way the compressor i was using was going to shift the piston



william

I use an old set of piston ring pliers to grab them from the inside. I think something like a battery terminal spreader would probably work on the rear pistons since they are so small.

mine was the same

use brake cleaner gradually pushing them in and out with a lever behind the pads every time they move a fraction clean all around then more brake cleaner it takes a long time but it works
Worst thing to use is WD 40 it does not clean them
My back brake is fine now

brake cleaner is always the safest cleaner to use with brakes,not worth the risk!!!

i do rate wd40 very high on cleaning items and i can't see how it wouldn't clean your brakes.wd40 shifts the worst build up of grime,caked on chain fling etc.


william

I too had a siezed rear, took it off the bike, pumped it till one piston started moving, then C-clamped that piston and kept pumping till second piston free.

Re-assembled after cleaning out the caliper and pistons, still doesn't brake well at the rears, No longer seized but no pressure when breaking .
I bled the breaks but still no dice.
Any ideas?

Sorry to hijack the thread like this.

I actually have the same problem as well. I think i might have air trapped in the system.. thats the only thing i can think of. When i get a chance im going to vacuum bleed them.

also try bleeding the brakes at the master cylinder,what a difference it makes and quickly.



william