Brake problems

I've got a problem that's driving me nuts. I've installed discs all the way around on a 1965 Cutl*** VC using calipers/spindles from a 95 Caprice on the front and C5 corvette calipers on the rear. I used an eight inch dual booster/master combination valve setup I got off the BIG net flea market that is supposed to have the disc/disc combo valve. The brakes STINK. Acts like a booster issue so I replaced it with another new one I had in the shop-same issue.
I pulled the master and re bench bleed it and still no go(stop).
Looking at the master, the rear is plumbed to the rear brakes, but the master was plumbed to the combo valve that way new so I didn't reverse it. I also wondered if I could have gotten the wrong combination valve but don't know how to ID it. Any ideas if this could be the issue? The master has approx. the same size res. front and rear so I ***umed it would be fine. Any thoughts on this, I'm about at wits end here.
Thanks,Hal

 

Most GM masters have the front brakes plumbed to the rear of the master. Not sure this would cause your problem. Is the issue that the brake feel is too hard, too soft, doesn't stop, or what?

 

what do you mean by stink? low pedal? soft pedal? hard pedal? firm pedal but just won't stop? be more specific please.

 

The pedal seems normal height wise and travel but requires a lot more pressure and much longer stopping distance than it should.
Hal

 

check to see if the push rod to the booster is to long i had that same issue once

 

Did you compare the bore size of a 95 Caprice master cylinder with the bore size of the master cylinder you put on the car?
I've had that work both ways. brakes that were so touchy that they required very little pressure and brakes that took too much pressure because the bore size of the master cylinder didn't match up with the calipers or wheel cylinders capacities.

Does the engine pull enough vacuum to work the booster right? A stiff cam might not give you enough vacuum to operate the booster effectively at idle speeds.

One other thing is that the supplied brake pads may not be on a par with what is on your daily if you have a high performance daily driver. Get out of a under 5 year old performance model car into a car that has base line brake pads and you are probably looking at a hell of a difference in stopping power and comparing one to the other. That's just something to ponder.

 

The master is the same bore size (1 1/8") as the caprice. It's a stock LS1 out of a 2004 GTO and the vacuum is fine. The rod to the M/C seems to be adjusted correctly with slight free play.
Even if I'd been sent the wrong combo valve, you'd think it would still stop pretty well as 70% of the braking should go to the front where most of the stopping takes place.
When I had a rear braided brake line built for the rear they made it smaller than I asked but you wouldn't think the stock size (for drums) would be much of a bottleneck if any.
Thanks for all your suggestions though.
Hal