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

[HO455]

Welcome aboard! We would love to see some photos of your truck. It must be nice to be the original owner.
Your reading of 720 psi is definitely considered low. Have you checked the pressure at the rear brake cylinders?
I don't believe that changing your proportioning valve will do anything to increase the pressure at the caliper. At least not enough to get your pressure up to 1000 psi or so as that would be the goal.
See the 1st link for some more information on pressure valves and the 2nd link for help locating the fault.
What brake components have been replaced over the years?
What style of brake booster are you running?

https://techtalk.mpbrakes.com/how-to...valve-overview

https://info.mpbrakes.com/faqs

[allen71]

Booster is stock single diaphragm and has been replaced. Stock 1/2 ton master cylinder has been replaced. My question is not, "will a 3/4 ton proportioning valve increase brake pressure. It is "is there a difference between a 1/2 ton valve and a 3/4 ton valve. I'm going to change the booster and master cylinder to the 3/4 ton units. I'm trying to find out if I need to change the proportioning valve also?
Thank you,
Allen71

[04ls1gto]

I put a CPP hydorboost in and was night and day vs the vacum booster. Well worth the money

[allen71]

04ls1gto,
Thanks for your input!
I've thought about a hydro-boost unit. What happens if the engine stalls? There are electric units that generate their own vacuum, I've considered that option also. In both cases "cost" is an issue for me, I'm working an a shoestring budget these days.
Allen71

[04ls1gto]

Originally Posted by allen71

04ls1gto,
Thanks for your input!
I've thought about a hydro-boost unit. What happens if the engine stalls? There are electric units that generate their own vacuum, I've considered that option also. In both cases "cost" is an issue for me, I'm working an a shoestring budget these days.
Allen71

If you can source used units it can be done for short money

[FLYNAVY30]

Allen, welcome! I just went through this on my '72 C20....I think this thread will provide all the information you're looking for...


https://67-72chevytrucks.com/vboard/...d.php?t=805668


Cheers,
Greg