1987 GMC brake problem.

[Guest Rocket455]

My 1987 3/4 ton gmc w/ 1975 dana 44 front end and 1975 3/4 ton rear end has no brakes and I cant figure out the problem. I have just put in all new brake lines and brake hoses, new master cylinder, new calipers, it has fairly new pads and rotors what could be the problem? any help would be greatly appreciated thanks..

[F&J]

They have a inline proportioning valve with it's built-in safety valve. The safety valve shuts off either the rear brakes or front brakes if there is a leak.

When you bleed these systems, the GM service manual says you need a special tool to hold the "pin" in on that valve. The pin is under a black rubber boot which will come off. The tool is little more than a bracket that bolts to the valve, and the other end just holds the pin.

Then you can finally bleed both brake circuits.

Some can be a pain to bleed out without a pressure bleeder...but it can be done.

[keiser31]

Just a reminder...adjust first then bleed.

[Guest Rocket455]

Thanks for the tips I really appreciate it. I did not know of needing a tool for the proportioning valve I will give it a try.

[old car fan]

Also,just because it is a new master cylinder,does not mean it is a good one.I have seen junk rebuilts.