MCPV-1 system not working well

[mbwicz]

I've got a 72 Lemans, 11" booster, 1-1/8" MCPV, wilwood D52 2-piston calipers on 11" rotors, wilwood 4 piston 11" rear disc system. I've got about 14" of vacuum at idle, and driven about 800 miles (using supplied wilwood pads). According to several people that I talked to when buying parts, this system should work really well (one guy said I needed 18" of vacuum). The system does not stop well, and the pedal is very, very hard. the master cylinder adjustments are full out on the small and large set screws. I have not checked pressure at the calipers yet, but have verified that all 4 rotors are hot to the touch (ok, burned a finger) after a reasonable drive.
My gut feel is that I need to step down to a 1" master to get more pedal travel and reduce fluid volume. Does this make sense, or should I check something else before spending another $200?
What is a reasonable (or ideal) pressure to have at the calipers?
It is to the point that I avoid driving the car because I'm not confident in the brakes. I replaced the original booster with a repop with no improvement.
Comments welcome. Please don't yell at me for keeping 11" brakes..........

Thanks,
Mike

[CPPAaron]

18" of vacuum is a minimum to get the power booster to work. It is actually harder to stop a car with low vacuum though the booster then it would be as a manual brake application. You also dont mention what diameter wheels you are running? The 11" brakes work great on 15-16" wheels were a 17" or larger wheel car will not stop as well due to more mass of wheel turning and its harder on the brakes. That is why on a 17" or larger wheel we recommend stepping up to the 12-13" brake systems.

[mbwicz]

Thanks for the reply, I'm running 15" wheels, that is why I stuck with the small brakes.

What pressure at the calipers would a properly operating system have?

Do you have any solutions to offer? Would switching to the 1" master cylinder be a viable option?

Thanks,
Mike

[CPPAaron]

a 1" master might help. You really need to get the vacuum up with a supplimental pump:

http://www.classicperform.com/Store/1947_59_Trucks/VP555.htm

or upgrade to a Hydralic style booster:
http://www.classicperform.com/Store2/Hydraulic-Brake-Assist-Systems.htm

[mbwicz]

Just an update for those who will read this:

I added an electric vacuum pump kit (I mounted it in the right front fender between the inner fender and radiator support). I had a pressure gage that I installed into the left front and left rear caliper. The front caliper maxxed out around 1200 psi, and the rear reached about 950 psi. A quick drive showed me that the pedal feel is much better than it was with engine vacuum, but the braking performance did not feel much better than what I remembered. Tomorrow I will get the car out and put some miles on it (it has been about 8 months since driving it, so I will bed in the pads again).

It was also good to see that the adjustment valves work as described in the instructions (pressure reduction only occurred in the rear only).

A question for Aaron: Are the pressures that I see in my car reasonable, or should I look to reduce the master cylinder size to get more pressure at the caliper?

The good news is that I have much more confidence in the brakes and look forward to putting the miles on.

Have fun,
Mike