Master Cylinder Bench Bleeding


The master cylinder has to be bench-bled, since once it is installed (at the angle it is meant to be installed at), there is no way for the air in the bore to escape. You have to bleed it level; there are kits to do this, or you can just use some old brake-line bent to feed back into the MC.

Once you have it level, put it in a vice (recommended; tough to hold it level), and use a 1/2" drive extension at least 8" long to push the piston in the bore. Air will come out through the lines, but also back up through the cylinder; you can even see the bubbles that are trapped in the cylinder as you look down into it. You have to do this about two-dozen times to get *all* the air out from the internals of the MC, if any has been allowed to enter (even if you run the cylinder dry during regular bleeding).

Once all the air is out, leave the bleeding setup on the MC and install it. Then *quickly* disconnect the bleeding lines and reconnect the brake lines one at a time. _NOW_ you are ready to bleed the rest of the system. Manually, you start from the furthest wheel; with a vacuum pump, you start with the closest (in actual practice, I don't think it makes any difference whatsoever). Tapping the lines, cylinders and junction block while bleeding may help you get trapped bubbles out.


Submitted by: Doc Barry