Plugged port method for bench bleeding a master cylinder. I won't type this out again so someone should save it and stick it in a readily located place for future reference.
Most BB (bench bleed) a master using the little hoses that circulate fluid out of the bore back into the reservoir. The problem with that method is it is very slow, not very effective, and tells you nothing about the condition of the master or how well you have managed to remove the air.
The PP method tells you if the master is good, whether you have the air out, and gives you a rough idea of how much you have to extend or shorten the booster push rod.
Acquire plugs that seal off the two ports in the master. If you have the little hose kit, you can put screws in the holes after you cut the little hose barbs off.
Put the master in a vise clamped ONLY on the flange. Never clamp onto the body where the bore is.
Plug the ports, fill reservoir about half way with brake fluid.
Loosen the port plug closest to you and push the master PR (push rod) all the way in and hold.
Close the port plug and let the PR back out.
Repeat until fluid is present at that port. Close the port plug.
Move to the port furthest way and repeat the process.
Once you have fluid at both ports and the plugs tightened to seal them off, continue pushing the PR in and letting it back out until it will only allow about 1/8" or so of movement. Generally about 4-7 cycles and it will come up solid. Solid tells you there is no air in the bore. Start to finish after the ports are plugged is about 2 minutes generally.
1- that little bit of movement is important. It tells you the master is good. It is the distance the pistons move inside the bore past the ports that let fluid into the bore from the reservoir. They have to move past them to build pressure and push that out to the wheel cylinders. Otherwise, all the master would do is push fluid back up into the reservoir.
2- the ports also exist to allow the normal expansion of brake fluid as it gets warm. If the fluid can not go back into the reservoir as the fluid expands, the brakes will self apply.
3-the PP method lets you check to see if fluid is bypassing the cup seals. If you can't get it hard to push and locked up solid after that 1/8" or so of initial travel, the cup seals are likely bad or similar.
4- some masters have 1/16" and some have a lot more. Pay attention to it so you can adjust the booster push rod as needed.
After the BB, get the crap out of the way in front of the booster, remove the vacuum seal from the master and slide it on the studs. Square it up and see what the gap is when you feel the booster gently bottom out on the booster push rod. It should be roughly about .030 or the thickness of 2 typical business cards. If it is more, you run the risk of pushing in the booster push rod and moving the cup seals past the ports. That can make it very difficult to bleed the system.
If it is less, you are adding pedal travel unnecessarily. The end of the push rod is adjustable. Grab the splined area below the hex with some needle nose vise-grips and turn the hex with a 7mm nut driver.
Once adjusted, reinstall the vacuum seal and finish the install.
This method has worked for us every single time without fail. No other way has been this effective.
