Bleeding the back brake!!!!

[Long John]

Well it's been a few weeks and regular dates with you tube and any forum that offers a glimpse into the impossible world of bleeding brakes. Replaced the lines on my ZX6R and serviced the rear calliper. So far so good, the fronts all fine and withstood a good workout at the Odiham ARD in Sept. However, the rear will not play along or hold any pressure, any advice would be gratefully received. Here' a list of my efforts to date.

Reverse bled the line, 3 times so far
Stripped and replaced seals in calliper and rear brake master cylinder
Removed calliper and elevated whilst bleeding
Applied pressure to pedal overnight before bleeding the next day also with calliper elevated overnight
Cracked banjos in desperation to try and find any air when bleeding
Pushed the piston back into the calliper and bled, at last, signs of correct pressure

Then just when I thought I'd cracked it, pumped brakes and no real pressure ???? I'm sure there are a few other things but I let you know if anyone mentions them. By the way, no sign of any fluid leaking. Typing from the garage to distract myself from attacking bike with more abuseAny suggestions????? Cheers John

[Snowy]

Did you prime the master cylinder with fluid? If not, that might well be full of air.

[Long John]

Just checked and master cylinder appears full, didn't consider this as I reverse filled the system through the calliper. Thanks for the idea.

[mikeapm]

bike shop! top marks for persistence though.

[Red Zed 1]

the age old method of tube from nipple in jar of fluid,operate lever several times then open bleed nipple as the lever is pressed then close nipple with lever fully pressed,repeat process until fluid runs clear(no air bubbles)might take a few attempts but always works for me..
if you need a hand then i could come over to help..
where are you at??

[Long John]

Thanks for the offer Al, should have mentioned I've been trying this method. All OK, no bubbles and fluid is moving through the system. The mystery to me is, how am I managing to get the pressure once the piston is pushed back into the calliper, but the pressure drops once the piston moves back to the operating position? To keep the piston back in the calliper I inserted a strip of 3mm aluminium between the piston and disc to get the piston right back into the calliper. Must be something up with the calliper/piston assembly, possibly?

[wheelers]

it sounds like the seals are gone in the master cylinder, as you operate it is supposed to stop pressurised fluid passing back only when pressure left off. if every other thing you have tried has failed sounds like the seals. should be able to get a rebuild kit.
when piston is back there is no pressure so piston goes out. when it hits the disc the seals keep the pressure on.

[Long John]

Thanks for the thought, I've rebuilt the master cylinder using a kit and everything seems to have gone back as it should and all the bits were the same as I removed, no leaks or other concerns. My thoughts were the same as yours initially so I went with the kit. If I couldn't achieve the right feeling with the piston back in the calliper I would strip it again and check the assembly etc... but I guess it wouldn't work by creating any pressure if it wasn't working.

[8_ball]

is there anyone you can ask to try another master ???? to eliminate the possible problems ???
as for adding extra strips or stuff I would remove them and leave well alone,
instead of feeding the pipe back into a jar feed it back into the res' at least that way you dont have to keep topping up and waisting fluid.
DOT 5 fluid ??
Id be more than happy to help, brakes can be a pain in the .......
off the bike is always the best way
oh and what state is your pipe in ???

[Mal103]

Another couple of ideas for the cooking pot although it sounds like you know what you are doing and have tried most things.

Take out bleed nipple and add some thread tape (plumbing supplies), stops any fluid or air passing along the threads.
Open bleed nipple a few turns and pump lever fast a few times making sure the res doesn't run out. This used to work on old Land Rovers as a small bit of air would trap inside and need forcing out.
Sounds like you've tried positioning the calliper so nipple is uppermost, also pushing the pistons back in and locking them in place whilst pumping lever. This works for poorly designed callipers where the nipple is not at the top/uppermost point.
The tube from the nipple should also go up for a bit before going into the jar/res so if any small bubbles do come out they will keep rising.

All else fails hit something with a hammer - old Land Rover stress relief trick...