Master Cylinder Autopsy

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dibbons

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This rebuilt master cylinder was installed more than ten years ago (photo #1). Recently, I found it empty and the brake pedal going all the way to the floor (the '65 Valiant Signet convertible it belongs to had been parked and not driven for a long, long time).

On the end of the piston (just above to where the screwdriver is "pointing" in photo #3) there was a small, dark glob of some kind of muddy substance. Inside the master cylinder bore at about the same place, the bore is now pitted.

According to the '65 FSM (blow-up diagram on page 5-9), a washer is to be used between the end of the piston and the primary cup (the primary cup is placed on the right side of the spring in the photo). I did not find this washer upon dis-assembly of the previously rebuilt master cylinder, I don't know what purpose it would serve, and I don't know if it being left out contributed or not to the failure of the master cylinder.

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Different manufacturers make their M/C and kits differently. At the time of the FSM they may have shown a metal cupped washer ahead of the primary rubber cup. This centers the spring and supports the rubber cup on the return stroke. No crud should be in the M/C, this is a lack of maintenance. Your concern should be of the pitting in the bore. If extensive, a hone will not clean it up and a rebuild kit will not seal. It may be wise to replace the M/C.
 
FYI, the washer in the factory diagram looks like a plain flat washer. Agreed, the M/C is toast (there are companies that sleeve the bores, I suppose for vehicles that don't have aftermarket parts available).

I could not find a rebuild kit for the M/C anywhere online, except for a couple of 50 year-old NOS kits that cost more than a rebuilt unit.
 
Not sure how original you want the car to be but that looks like a single piston master. For safety sake, I think I would replace it with a dual piston and run new brake lines as needed.

If you do decide to do that, I would really recommend using DOT approved copper/nickle alloy brake lines that are available and the reason is because they are extremely easy to bend, double- flare and believe it or not, they don't work harden so if you make a mistake you can re-bend.
 
Manual and power brake listings for M/C show different part numbers, but they are both 1" bore size. The pushrod arrangement must be different.
 
A dual-piston MC would be safer, and was a fed mandate ~1967. Search for my post using a 1999 Breeze MC on 2-4 bolt adapter plate ($30 ebay) in my 1964 Valiant w/ manual brakes. I likely gave the PN's for fittings to connect new tubing to your existing distribution block and rear tube (bubble-packs at Autozone). The brake pedal wound up in the same place. Loosen the brake pedal switch and re-adjust when done. It shouldn't restrict pedal motion.
 
I'm not going to debate the pros and cons of dual systems vs. single systems. I will say though that the last time I checked (which admittedly has been years ago) there had not been one accident chargeable to the failure of a single system brake configuration.
 
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