Brake Problems

[howlinwolf]

Several years ago, just before i took the truck off the road, the rear brake wheel cylinder failed. that was 2 or 3 years ago. well i have been working on it.

so far i have a *new* driveshaft (straightened, and new yoke and u joints
new front upper and lower balljoints and tie rod ends
serviced front axle, inspected brakes

now i have also replaced the rear shoes and wheelcylinders, and after bleeding there is no brakes on the back. there are no leaks and it has been bled and rebled and readjusted as well.  now as long as it sat with no fluid to the rear, could the master cylinder have failed?

its a 78 chevy k10

[Irish_Alley]

whats it doing?

[howlinwolf]

the back brakes wont engage at all with the pedal. the ebrake works fine, but the back drums wont engage and stop the wheels from turning. there is fluid and everything is bled, but there is no movement on the back brakes with the pedal.  the front brakes are fine.

[Irish_Alley]

Not to offend you or your skills but did you adjust the rear brakes

[howlinwolf]

hey no offense there. everyone makes stupid mistakes sometimes. yes, there is a light drag when you rotate the drum. but i had my wife press the brakes, truck running with a drum off, and nothing moved at all.

[Irish_Alley]

brake light? hows the pedal?

[howlinwolf]

no light, pedal feels the same as it has since i got it back out. there is a lot of drop before engagement.

[howlinwolf]

for me it seemed when i bled it there wasnt much pressure when the pedal was pressed

[Irish_Alley]

hate to say i dont know much about brakes. but i think the proportioning valve can go bad(most time under panic braking as its setup to be open until then) also, the rear rubber line (this most time causes the brakes to lock up) i want to lean to the master cylinder being bad. but i dont know how to check it. could the brake line of rusted on the inside and clogged itself? idk i would think the only way to see this is to undo the metal line and see if theres any difference in the amount of fluid that gets pushed out

[bake74]

     You are going to have to pressure check the rear brake system, each side starting at the backing plates of the rear brakes.  You need to eliminate as you go forward to brake master cylinder to determine where the problem is or if you might have more than 1 problem.
     I would think along the lines of the either brake master cylinder first as Irish said, or second proportioning valve, though these are less likely to fail.

[howlinwolf]

went ahead and replaced the master cylinder since it was under warrenty, still having problems. but now i have help

[howlinwolf]

there is what seems to be pressure at the rear when i bleed, but it wont move the wheel cylinder. the one im checking is new, but there is no movement.

[bd]

Does the brake light in the dash work with the e-brake set, key on?  Your description sounds much like a tripped combination valve. 

[howlinwolf]

Actually no. Where is this valve. Plus the springs are getting replaced tomorrow. Its all droopy looking compared to fresh rebuilds

[Irish_Alley]

the valve is on the cross member in front of the engine, follow the brake lines and it will lead you right to it. but i would crack the other lines from the rear and check the fluid there then move up to the next spot where you can open it