Master cylinder problem

[Guest]

I have a rebuilt master cylinder i am trying to put on my bike, but there is a problem.
When i pump the lever to bleed the brakes there is no pressure building up, some air bubbles surface, but no pressure.
I have removed the lever and pushed the piston all the way in first, then tried pumping it after that, but still no joy.
Any ideas?

[Dogma]

Did you clean the teensy tiny return hole under the reservoir? It's about 0.5 mm in diameter, so some overlook it. Once that's clear thought to the main bore, do what you have to do to put a vacuum on on of the caliper bleeders. Pull some fluid through to prime the master and you should be able to start building pressure with the lever.

[waterman]

There is still air in there somewhere. Try first to bleed air from master cylinder by disconnecting hose at master cylinder, pump until nothing but fluid. Reattach hose to master cylinder and pump hose full of fluid. Repeat with splitter, and then with calipers.

It can be a pain since air bubbles want to float and the hoses travel down the forks. Ideally, you would arrange hose and calipers above master cylinder where air would collect in calipers and thus bleed easily.

Good luck, and hopefully you bought a quart of brake fluid.

[kng254]

Let it sit over night with the lever pulled in the air bubbles will rise on their own.
Then try again.
I've bleed my brakes and though al the air was out and they were still mushy did the overnight thing and all was good.

[landshark]

Thanks for the replies guys, i am thinking that my bleed screws might be leaking. I am going to grab some new ones and see how that goes.

[kng254]

If there's no fluid weeping then there is no need to replace the bleed screws

[nufnuf]

try bleeding with suringe method
That way the air bubbles can be forced out at your leisure
(careful of the blowback at the master cyl resevoir)
works like a power bleed
cleanup with warm soapy water (lots of it if you are as messy as me)

[OldVet66]

Vacuum to pull the fluid up from the bottom of the brake lines work nicely, with a minimum of bleeding afterword. They don't like to pump down when they are empty for some reason.

[jwhelan65]

Keep pumping it takes awhile...

[SqDancerLynn1]

What you need to do first is bleed the master cyl then hook it up