68 Brakes
 

Don't drive my 68 GTO much, because the brakes are CRAPPY! Replaced M/C, with a rebuilt, rebuilt calipers, wheel cylinders, and SS brake lines about 2 years ago. Brakes were acceptable. Drove it last fall, brakes were spongy. About 3 months ago, got in, and the pedal went to the floor. Front reservoir was dry. No visible leaks anywhere.Refilled the other day, tried bleeding calipers, no pressure. Thinking M/C is kaput.

Who makes a decent M/C for these cars. 4 piston calipers up front. Tired of the AutoZone Advance O'Reillys rebuilds that don't last. Does Wilwood, or anyone like that make a bolt up M/C, for these cars?

Also, on the side of the M/C is a valve of sorts, that goes in the line, from the front reservoir, to the prop valve. What purpose does that valve have? Residual pressure for the calipers?

Possible it is leaking into the brake booster, look for drips down the bottom center of the booster.
RockAuto sells brand new AC delco master cylinders. In fact I have an extra I could sell you quite reasonably, bought one and never ended up using it.

Does your mystery valve have a black rubber button on it?

Is the valve you are referring to?

If yes, then it is a Hold Off Valve that forces the rear drums to actuate first.

https://forums.maxperformanceinc.com...4&d=1658513089

Yeah, that's the one.Never knew what it was for.

I don't see fluid on the booster, I would think the rear reservoir would empty first, if it was leaking from the M/C. Rear reservoir is fine.
The pic of the AC Delco M/C on Rock Auto shows something different than mine. My M/C has the 2 bales to hold the cap down, the one pictured has a bolt in the center, to hold the cap on.