Hard pedal-'67 El-Camino

[Matt Ringer]

So I purchased a complete front drum to disc setup from CPP a couple years ago and installed for a friend of mine. The pedal was always hard, as if there is no assist. At the time it was a 283 and pulled around 18" at idle. Car has a vacuum bank.
Last month I swapped in a mildly built 383 small block, with a 700R4. Brakes are still hard and I have the time to fix it, so I started diagnostics.
So far-
* Checked clearance of pushrod from booster to master. .010"
* Checked for air leaks on Booster with a gauge. Booster is sound
* Removed and checked Master for leaks. None
* Tested assembly in vehicle with a vacuum pump and gauge installed. At 28" it still acts as if there is no assist. The pedal is only slightly easier to apply.
* The CPP supplied proportioning valve is installed and centered
* The car, under no circumstances will lock up the brakes

I called CPP with my issue and spoke with Danny, who agreed with the diagnostics of a bad booster. I purchased the components at a local hot rod shop and and Danny said just go swap it out, they would handle the warranty.
Dreamers no questions asked, swapped out my components, with no hassle. I wholeheartedly applaud this company for it's understanding and willingness to help where it can, great customer service.
Now, onward. New Booster installed, pedal is slightly better feeling, but brake feel and performance are nowhere near expectations. Like I said, it will not lock up even on a smooth concrete floor. I will hook up pressure gauges today to check applied pressure, but what about pedal feel?
I do not want to randomly return components, even under warranty. It is costly to both the company and to the person attempting the repair.
Any pointers will be appreciated-
Thank You all
Matt Ringer
425.239.5562

[CPPAaron]

Good Morning,

A hard pedal sounds like a lack of vacuum and typically is. The vacuum has to be measured at idle. Also, I dont see what size booster was supplied in any of these. You can check your Cam specs and see what the cam manufacture shows for a vacuum draw. Let me know on both those questions.

[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