Master cylinder overtravel

[SwiftDB4]

Is it possible to overtravel A Girling type master cylinder and damage the internals? I have 2 OBP (Girling clones) cylinders on a balance bar.

[jbcollier]

No, they can bottom out without damage.

[SwiftDB4]

Thanks for the reply. My dilemma is one m.c. bubbles air back up into the reservoir. This is the second OBP m.c. that I have tried. There is no leakage at the outlet. Initially the crush washer on the inlet leaked some and I replaced it so that no leak now. I've bleed about 2 qts. thru the system, but still soft on that cylinder. Any advice?

[Pfreen]

I bleed my brakes by running a clear tygon hose from the brake bleed nipple back to the reservoir, when the fluid in the system is new and clean.   That way, you pump the brakes until no bubbles, and you don’t have to worry about running the resvoir dry.  It saves on brake fluid as well.

[jbcollier]

Take the master cylinder off and bench bleed it.  No bubbles when bench bleeding means the problem is elsewhere.

[Pfreen]

Jb, please explain to me bench bleeding. I know how to do it on a bench, but it seems to me the fluid will leak out during installation, since the outlet ports are open.  How do you prevent this from occurring?

[jbcollier]

Bench bleeding properly primes  the cylinder and purges all the air out.  What little air that may get back in is then much easier to bleed out.  I use rubber plugs after bench bleeding, and I let the unions "flow" a bit before snugging them up.  When bleeding the system, I start at the master cylinder outlet.  When we changed master cylinders, ones that bypassed, often that is all that would be required.

Bench bleeding will require a reservoir hooked to the m/c inlet and then a pipe from the m/c outlet back into the reservoir.