Suburban brake problem. 1987 w/ 454

[Davidh]

I posted earlier but put in the wrong spot. I have 87 suburban with 454. The rear brakes are not working. I went to bleed them and am not getting any fluid from the rear brakes. The pedal is spongy and goes almost to the floor. I am getting fluid to the rear proportioning valve that is attached to the . But the wheel cylinders are dry. I s there another valve somewhere. Is there a way to test the from proportioning valve?

[RayVoy]

Disconnect the rear side of the valve, have someone push the pedal, no fluid equals bad valve.

[Davidh]

Took the wheel cylinder off the right rear and pumped the brakes. Got a good stream out of the brake line. got new wheel cylinder and will put it on. Is there a way that the cylinder could be clogged and not bleed.

[Davidh]

Took off wheel cylinder and got a good stream from the brake line when brakes pumped. Will replace the wheel cylinder . can the wheel cylinder get clogged and not bleed?

[Davidh]

Disconnected the rear side of the proportion valve get a weak stream of fluid. With the rear wheel cylinder off I get a stream but it is not strong. petal is mushy. brake light is on I have replaced the master Cylinder and bleed the front brakes. get a little fluid form the rear when bleeding. I used the cap from the new MC and blocked off rear line of the MC and got a full pedal. Here is my question can the proportion valve be bad and let a little pressure out but not enough to activate the brakes or is it one of those parts that either works or does not?

[Davidh]

Have put on a 2nd master cylinder. The first one was leaking. A right rear wheel cylinder. Getting a little fluid out of the new wheel cylinder. disconnected the rear line to the proportioning valve and got a little bit of flow. I am pulling the proportioning valve. and replacing it as I expect it is partially plugged. I am thinking of putting a used one one as I cannot find anyone in my area who can get a new one.

[Davidh]

Have now put on two master cylinders. The first one was leaking. Replaced the rear wheel cylinders and the proportioning valve. Again tried to bleed them and get just a trick out of the right rear wheel and nothing form the left rear wheel. Uncoupled the rear line form the proportioning valve and get fluid but not a strong stream. Should I be getting a lot of fluid out of the proportioning valve. it seems like no pressure. Do these valve need to be reset? I checked all the lines and not kinks or breaks in the lines.

[vncj96]

with something that old it mught be wise to just do a full break line replacement, could be filled with gunk or debris

[Davidh]

Is changing the lines pretty complicated? I was considering disconnecting the line and blowing them out.

[RayVoy]

The lines are steel, they will rust and corrode. New lines would be the best answer if they are that plugged. A hard stop would probably blow one of the lines.