72 Brake Problems

[RB72]

I cant figure out what is wrong with my brakes on my 72 K10.... I have replaced the rear wheel cylinders and break pads and it seems like it is getting air in the lines somewhere, but all of my brake fluid is still in it and nothing is leaking out... If I bleed the brakes then they stop good for the first drive then the brake light comes back on and it will hardly stop..... should I try bleeding the master cylinder or what? Thanks in advance!

[71chevc10]

sometimes the rear rubber hoses collapse internally if they are old
bleeding the lines fully i had to do it several times among other issues

[71chevc10]

if you have a ccp proportioning valve you need to use the screw in tool to keep the piston in place so it doesnt shut off the rear brakes while bleeding them

[RB72]

How do I know if it's a CCP proportioning valve?

[HO455]

Post a picture and maybe someone can ID it for you.

[RB72]

Should I take the tire off to take the pic? Or would a top view work?

[Mike_The_Grad]

If you're experiencing brake fade, ( Like when you're at a stop light applying the brake pedal and you start to creep forward without lifting your foot so you apply more pressure to the point where the pedal is basically on the floor.) then you have a bad master cylinder.
The master cylinder can develop a "Internal Leak" where the interior seals of the master cylinder fail and fluid pressure loss occurs. It will not leak externally and will not lose any fluid, but it fails to contain the required fluid P.S.I. for proper brake operation.
Your brake booster (if you have one) does not and will not affect your braking systems ability to stop your vehicle. The brake booster is solely responsible for -assisting- in the application of the brakes. If your brake booster were to fail, you would still have complete control and ability to apply the brakes, it would just take a lot more effort on your part to apply the brakes.