M C Bleed

[Joe C.]

Has anyone successfully bench bled a 1965 OEM master cylinder without damaging the internal seals, or must this be pressure or vacuum bled only. Thanks in advance.

Joe

[John H.]

Re: M C Bleed

Joe -

I've bench-bled both the manual and power versions with no problems; are you having a specific issue with the seals?

[Gary S.]

Re: M C Bleed

Ditto on both power and non-power bench bleeding. No problemo.
Gary

[Joe C.]

Re: M C Bleed

John:

I have bench bled other masters in the past with no problems, but this time there is an issue which I have never faced. The cylinder came packed with a warning label advising against bench bleeding. It further states " due to the OEM style of the internal seals, this unit should be pressure or vacuum bled only".It is a reproduction Bendix 2225032 non power unit used in 1965. I am not sure if the manufacturer (??) is just being overcautious--again, I have never seen a caution against bench bleeding.

Regards,
Joe

[John H.]

Re: M C Bleed

Can't imagine why they would include such a warning label; forces on the seals during bench-bleeding are the same as those introduced during normal operation. The only change that was made to the OEM seals in the mid-60's was to modify the lips to accommodate the high vacuum/pressure condition introduced through the compensating port for the new assembly plant evacuate-and-fill equipment. Prior to that, plants bled brakes at the wheels with vacuum hoses.

[Doug Flaten]

Re: M C Bleed

Possibly they may be referring to procedures used when they have just slapped in a rebuild kit. With a rebuild kit, you have the possibility of damaging seals if there is a little pushrod wear or bore wear. Manually bleeding strokes the piston farther than normal brake operation and seals can get scratched on a dirty or corroded push rod. Pressure bleeding allows you to bleed without stroking the unit. If it is going to leak as a result of manually bleeding, it is likely just a matter of time before it leaks under normal operation.

[John H.]

Re: M C Bleed

Scary, if they just "slap in a rebuild kit"; a perfect bore is absolutely essential to both function and long-term reliability. That's why I always send master cylinders to White Post - they bore it, sleeve it with brass, and bore/hone it again to exact size before installing the kit. There's some pretty scary "rebuilt" stuff out there on store shelves.

[Joe L.]

Re: M C Bleed

John-----

Yes, "auto parts store type" rebuilt brake master cylinders are to be avoided. These things are usually very cheap and are not even worth their cheap price. They're often a clever way to obtain an original core, though. However, that's all they're good for. For use on a car "out-of-the-box", I wouldn't touch one with a 10 foot pole.