Brake Bleeding Troubles

[a67]

The only way to tell what size the M/C is is to measure it. May be able to do this without opening the system. Need to access the rear where the pushrod enters. Then measure across the bore, dial calipers are best, but a small 6" machinists rule can also be used.

Since this was a rear drum setup the M/C may have a residual pressure check valve in the rear brake port. If so it must be removed, otherwise the rear brakes will drag.

I've found that bench bleeding a disc brake M/C via the looped-back tubing into the reservoir doesn't work that well. The reason is the lack of residual pressure check valves. Stroking the M/C just moves the fluid and air back and forth between the bore & reservoir.

I've moved to the plugged port method of bench bleeding. Sometimes plastic plugs are included with the M/C, else make up two plugs from brake fittings that plug the front and rear ports. Then stroke the M/C with the nose pointed slightly downward. Note the bubbles that come up through the compensation ports.



Once they stop and the M/C locks up solid with a short stroke, maybe 1/32", it is bench bled. Mount on car, then remove a port plug and quickly install the line for that port. Then do the other line and finish bleeding the entire system,

Bob.