After not driving my 68 Dart since March (brake troubles, no time to fix with crazy schedule) I finally had time to put in a new (rebuilt) master cylinder this evening. The problem is, it won't bench bleed! I spent well over an hour on it, one stroke every 10 seconds or so, and STILL have air coming through the recirculating tubes. The master is a "Fenco" rebuild, I think.

I'm guessing that in some manner the replacement master must be bad. Perhaps it is drawing in air along the piston shaft seal... I don't know.

But I do know that my faithful old Dart (which was scheduled for some minor bodywork and paint this August) is rapidly becoming a liability rather than an enjoyment. This car IS (supposed to be) my daily driver.

I need both encouragement (I'm ready to sell it and buy a used Honda) and a technical solution... anyone up for both?

Thanks- Mac

Are the brake bleeding plugs airtight? They can have a tiny leak and suck air back into the master cylinder when the piston is released.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Remanufactured ≠ new.
Assuming, as has been posted already, that the bleeder fittings were threaded in properly, the odds are you got a bad "remanufactured" master cylinder.

Remanufactured parts, especially for old cars, tend to be much more problematic than new ones or genuinely-rebuilt ones ("rebuilt" means a skilled craftsman does the job on a workbench...such parts do not come from the parts store).

What brake system do you have? 9" drum, 10" drum, disc?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Hello Dan,

9" Drums all the way around. It is slated for a disc upgrade, and I have a donor all lined up, but I need to get it running (or stopping
) so I can get it to VT where I can do the swap.

And yes, remanufactured parts are frustrating!

-Mac

I agree on the possible bleeder line leak. Tapping MC with a hammer while benching can help loosen up trapped bubbles.

Lou

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Home of Slant6-powered fun machines since 1988

This may be interesting... In the bleeding process I have not observed the fluid ever returning back into the master (through the clear looped tubes) as the brake pedal is released. Shouldn't I see some backflow as the pedal comes up?

Still about 95 degrees here in Boston, so the master cylinder may have to wait until tomorrow night for an air-leak check on those bleeder lines.

-Mac