Braking Problem. Do I need a Vacuum Canister?
 

Since adding rear disc brakes my braking has suffered. When cruising down the road, the first time I hit the brakes they all grab really well. Each push of the pedal immediately after results in harder pedal with less braking action. If I need to quickly slow down after the initial pedal I have to really get on it. It can be a little scary at times. I'm guessing it's a vacuum issue but I'm not sure. Here is my setup:

New Stock 11" Vacuum Booster
71/72 Front Disc Brakes
Captainfab Rear Brake Setup (Camaro calipers)
CPP Master Cylinder MCPV-1 (has built-in prop valve)

The master cylinder is adjustable. I have pressure to the rear brakes set to max.
My cam duration 245/245 @ .050" lift

Re: Braking Problem. Do I need a Vacuum Canister?
 

It may be a proportional valve or adjustment problem

The front brakes are supposed to do the majority of the braking in a vehicle. Some where around 60:40 or 70:30 not exact on the numbers. If the rear are doing the majority of the braking it will be a lot harder to stop.

Don't overlook the possibility of collapsed rubber lines if they haven't been replaced.

forgot to include. It is possible the booster is at fault if it's losing it's vacuum but check the easiest and cheapest first.

Re: Braking Problem. Do I need a Vacuum Canister?
 

when adding disc to rear did you change to the proper master cyl and proportioning valves

Re: Braking Problem. Do I need a Vacuum Canister?
 

The master cylinder has a built-in prop valve and works with a disc/disc setup. My brake lines are stainless or steel braided with the exception of the short lines to the rear calipers. I will mess with the adjustment on the master cylinder and see what happens. I hate that my disc/disc braking is worse than my original disc/drum.
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Re: Braking Problem. Do I need a Vacuum Canister?
 

Have you done a vacuum test to see just how much it pulls at idle? thats what i would do if i had a cam that big in it.

Re: Braking Problem. Do I need a Vacuum Canister?
 

Depress the pedal several times and then hold the pedal down. Start the engine. The pedal should go down as you are pushing with the same pressure. If the pedal does not move you could have a vacuum leak before the booster or the booster could be bad.

Second test.
Depress the brake pedal with the engine running. Turn the engine off. The pedal should stay the same. If the pedal moves up the booster is bad.