Brake Problems

[EvanMember]

I had my rear calipre off to fix some damage, put it back on brakes were weak, thought maybe it was air (somehow).
Using a syringe i couldnt suck hardly anything, even with the nipple completly out, hardly any fluid would come out while pumping the pedal.
6 hours later ive tried it every way i can, ive Bled, reverse bled ,changed the master cylinder, pushed the piston back and fourth with pliers,cleaned the nipple, still cant get it
if i pump straight fluid up through the nipple the level in the resevoir moves up with no air bubbles but if i suck it straight back out its 90% air that comes out
all i can think is its somehow either getting in through the slave cylinder or the piston wich is well used and the dust seal is crumbling but the fluid seal should still be ok
there is no fluid leaking anywhere i can see
any thoughts? is there a way to test the slave cylinder?

[shaneMember]

I’m not real clever but if you’re getting air one way and not the other as you’ve described I’d say, yep, the seal in the caliper is your culprit. Without one in front of me and bear with me but I’d suggest if you remove the hose, block that hole with a bolt and introduce air into the caliper might be a way to test? If the piston doesn’t come out there’s your answer. Sounds as though you’ve pretty much narrowed it down anyway though.

I hate brakes.

Edit after a bit of sleep. It sounds like you’ve tracked the fault down to the wheel cylinder. If the dust seal is crumbling I’d say there’s a good chance the piston seal is perishing as well. When changing those I tear the system down. Blow it all out with compressed air. Wash and wipe down all parts (not the rubber) with metho and blow out with air again. Re-assembly is done with all parts lubed with the fluid you will use in the system. Put a new kit through the wheel cylinder then test it. You’ve already done the master cylinder, if it doesn’t work then you have a leak in your hose or banjos? But I’d be putting new seals in the caliper first.

[jamieMember]

hmmm must driving you nuts, sounds similar to an issue i had on my old wr250’s brembo’s.

Illl try and remember the order of stuffing around.

was loosing peddle all the time, no leaks at the dust seal,would bleed then be ok but come back to loosing peddle mainly on wet rides,put on 2nd hand master cylinder,couldn’t bleed it no matter what i tried,bike shop bled it in a minute as had a better syringe perfect brake pedal,old master cylinder packed it in a few months later,purchased brand new one and thought it would be a nightmare to bleed but was easy this time and never had an issue again.

What was wierd was there was no leak at all around the dust seal on the first master cylinder but if i went on a wet ride it seemed to pull water in and need to be flushed with the first master cylinder and you could visibly see the fluid contaminated. This made no sense as i thought if it’s taking in water it should leak some fluid.The 2nd had one just lost the seal and spewed out fluid so at least it broke properly.

Didn’t have any leaks around the caliper piston seals and didn’t have to touch them in the end. Don’t know if this is going to too much help but it sounds a little similar to the hassle i was having with the bleeding.

cheers good luck with it.

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