Hard pedal-'67 El-Camino

[Matt Ringer]

I measured across the face using large calipers, 10".600-O.D.
single diaphram. I'll go throw a gauge on it now and be back in a few. Give me a few... Thanks Matt

[CPPAaron]

What diameter?

[Matt Ringer]

O.K. Ran up to the local supply house and purchased the large mityvac compound gauge, ran in concert with the small one on the little hand pump, both were in agreement.
Idle vacuum- 12" Low, I know, but with a bank, after a couple blips of the throttle, it fell to 15". Step on the brakes, the gauge rose to 14". Let off the pedal, back to 12".
So it appears the variable chamber is being activated. Pedal travel is about 1.5" and goes rock hard there.
With the gauge still attached, and driving up hill, vacuum is between 4-8", no brake application. Turned around coasting in third gear, vacuum is at 21". Reasonable application of brakes the vacuum raised an inch and letting off the brakes, it raised a few more inches, but quickly fell back to 20- 21". (We're going back towards atmosphere, so that's why I call it raise) The car slowed somewhat.
After accelerating back to 45 or so, vacuum at 21", third gear, I applied the brakes fairly aggressivly, not dynamite, but smooth hard application. The pedal travel is around 1.5", with modest backfeed, then it won't go any further. The car slows down, but, if it were any other old rusty chevy, weaving down the road, I'd have been in the ditch sideways. I mean at least ONE tire would have broke traction! Anyhow, that's where I am. I guess I'll go buy some fittings so I can check applied pressure at the caliper. Any ideas? Thank You again! Matt

[Matt Ringer]

I called Dreamers, it is the Delco Moraine 67-72 SRV-OE. Does that make it an 11"?

[Matt Ringer]

With a 2000# pressure gauge installed on a metric bleeder screw, drilled through the end, it reads 700# with my meat footed neighbor mashing on the pedal. That's also with 22" steady at the booster, so I have low pressure at the caliper. Is this bore size, or a proportionong issue, or Master cylinder not functioning correctly. There are plugs adjacent to the outlets on the master, should I get into them for an output reference #? Thank You again...Matt

[CPPAaron]

What bore size master do you have?

[Matt Ringer]

It is a 1" CPP unit got with the kit..

[Matt Ringer]

OK, I got sidetracked for a few days on a late model Trans Am. Heads (ICK)
SO, Aaron, I checked for a more advantagous rod placement and can't move the rod up for more mechanical advantage, as it puts a strain on the pushrod. Don't want that, are there any other reason I would have low caliper pressure? Would it help to install a double diaphram booster? Any thoughts are appreciated,
Thank you again,
Matt