have 1992 chevy truck can not get back bracks to work properly?

Question

i have replaced brake lines from the rear to the front it has new cylinders in rear,new shoes,drums are good, i have put 4 new master cylinders on it ,new booster.i have taken the abs off of it,it had the rear wheel abs. it has been bleed properly many times. the front brakes work great NEED HELP BAD been working on this off and on for 3 months all new parts are new not rebuilt, portioning valve has been replaced to. my email [e-mail] help help

more info guys on this 1992 truck what we have done to it.we have plugged the lines off at the wheels and u cant move the peddle at all.when we only plug the the back brakes u can only move pedal have way front brakes work great.when we plug off fronts pedal only moves half way. but when we hook up front and back pedal goes all way to floor and u can pump the pedal 3 or 4 times to get some pedal but hwen u stop it just goes to floor we are bleeding brakes properly each time doing this.we are wondering if the abs has to be on this truck to make them .i took the abs off because it wasnt working it very expensive for this old truck. i have a 1996 monte carlo that i done the same thing to and had to problem doing this to it . email me with any info u have if u can thank you guys.

Answer 1

i know you have probably heard this before ,but the only thing it can be ,and i speak from experience is the proportioning valve,anytime you press the pedal you run the risk of off setting it,and that sounds like what has happened here,especially if you pressed it with all the bleeders closed on it,and I'm sure you did,open the front bleeders and hit the brake it should center it again,good luck.,,PS put a line on the bleeders to control where the fluid goes to.

Answer 2

It sounds like you still have a leak. check lines and remove rear drums to see if the new wheel cylinders are leaking. You didn't specify why they aren't working properly. If the pedal is low you can always clamp off the brake hoses to see if the problem is at the wheels or not.

Answer 3

Have you tied the load sensing valve to the rear cyls. open? many times this valve will keep you from properly bleeding the rear wheel cyls. This valve is usually located between the rear axle and the frame, its job is to manually sense truck bed height in proportion to ride height( as load increases, the valve opens to allow more fluid pressure to the rear wheel cyls.). If this valve is not held open during bleeding procedure, rear brakes will not be bled properly, in most cases.