new rear master cylinder,get the fluid to flow

I installed a new rear master cylinder and filled it. What is the best method to get the fluid to the caliper? I pumped the foot brake for a while with no success. This is one of the last things I need to do to get the bike on the road.

tshadow6 said:

I installed a new rear master cylinder and filled it. What is the best method to get the fluid to the caliper? I pumped the foot brake for a while with no success. This is one of the last things I need to do to get the bike on the road.

Click to expand...

When I do brake work, I pre-fill the brake line and the caliper with a syringe. Take the brake line to the bench, form a U shape, and fill the line using the syringe. Fill the caliper on the bike. Carefully connect the now full brake line to the caliper and to the M/C. Fill the M/C last. Very simple, and there's no air to bleed. Perhaps a small amout of bleeding needed as the last step.

Quite often a brand new master cylinder needs to be bench bled before install. You can try it on the bike but it's easier off. When mounted the hose from the reservoir to the M/C has a bit of a high spot that traps an air bubble. Make bleeding a PITA.
When I Added a rear disc brake the only way I could get it bled was to remove all the parts. Hold the reservoir up so the hose is straight, clamp the M/C in a vice. Fill reservoir, without the hose hooked up cover the hole with a finger tip. Now slowly pump the M/C. As the piston pushes out any air gets pushed past your finger tip. Your finger tip seals as the piston returns keeping air out. After a few pumps fluid should come out. This is the bench bleed.
To can now install or do as I did.
Once fluid comes quickly hook up the hose. Hold the hose up, Seal the hose with a finger and thumb. Pump, until fluid gets that far. Add the next thing to the hose. Eventually you will get to the caliper.
With it all bled, don't take anything apart and install on the bike.
You can try doing this on the bike but that high spot will make it tough. Once Bled as I mentioned and installed the hose won't have an air spot to try to bleed out.
Once done this way you can drain and flush refill with out any problems. Just pump out the old fluid and keep the reservoir full. Do the drain flush and refill this way and it takes about 1/2 to 3/4 of a pint.
Leo

I will try your method,thank you.

I use a Mityvac vacuum pump to get fluid through drained systems, then finish with the traditional hand bleeding.

this is a complete new brake set up. I removed the mc and piston and pumped the piston by hand to get the fluid moving. Now all I have to do is remove the brake piston and clean it up.

I have a Miti Vac, Works great on the front but it wouldn't work so well on the rear.
Leo

The "pre-filling with syringe method" works perfect everytime for front or rear brakes.