Brake Upgrade

[allen71]

I have a 1971 K10 Suburban, I've had it since new, ordered it from the factory. Years ago I put 12x16.5 wheels and tire on it and the brakes immediately became insufficient, to say the least. Then I rebuilt the motor with a moderate cam that lowered the vacuum, making the problem worse. I added a vacuum tank witch helped a tiny amount. This was back in the late 70's.

I rebuilt the motor again 5 or so years ago with a roller cam that increased vacuum at idle to around 18 inches of mercury (can't remember the symbol for mercury). Brakes still suck! Especially when I'm up in the High Sierras at 8 or 9,000 feet.

At home the brake pressure to the front calipers is 720 PSI.

So I'm going to change the 1/2 ton booster/master cylinder to the 3/4 ton version.

My question is, Is there a difference between the factory proportioning valve 1/2 ton vs 3/4 ton? They look identical but have different casting numbers on them.

Thank for your help,
Allen