67 manual brake master cylinder question

[Joseph E.]

I'm in the process of putting my original master cylinder back in and am at the point where I will need to bench bleed the unit. I've read the procedures about doing this that I located in the archives but I did not see mention of one detail. Can the master cylinder be bench bled with the proportioning valve already installed onto it? I'd like to remove the air from both the master cylinder and the valve so I have a minimum amount of air being put into the lines that will need to be bled out. Is this OK to do or would it adversely affect the valve? Thanks.

Joe 45420

[Larry M.]

Re: 67 manual brake master cylinder question

Joe:

The answer is yes it can. The valve block attached to the master cylinder is not a "proportioning valve", but is instead a "brake warning" switch. It contains a piston with an electrical contact that activates when the pressure(s) on either side of the piston is different (indicating a loss of pressure to either the front or the back brake systems).

It is not necessary to bench bleed the master cylinder and brake warning switch together, but it should not cause any problems/issues either. I have always bench bleed the master cylinder and then simply installed it and bled the entire system.

Larry