Lost my rear brakes only.

[rjfguitar]

I seem to keep losing the back brakes on my K5, but not all the time. I will take off, hit the brakes, have what feels to be all four, accelerate, and then at the next stop I only have front brakes.

This seems fairly simple since it's pretty much got to be either a master cylinder or proportioning valve going bad. I have never heard of a bad prop valve though. I've got new rear wheel cylinders in my 14BFF and there is no sign of leakage anywhere, reservoir is full. No ABS, it's an 85', you guys no what I have.

So....master cylinder or prop. valve? Or something I am overlooking?

As always, thanks.

 

[HELLBENT DESIGNS]

how old are the rear brake hoses? they can look perfect on the outside and be collapsed on the inside. when you bleed them do you get normal fluid flow?

 

[hi pinion]

Check your brake fluid

 

[FWP]

I'd put a new master cylinder in.

 

[Ryan B.]

I'd put a new master cylinder in.

Did you try bleeding the rear brakes again.. both sides.. just to be sure?
I guess i'd put a master cylinder in next.. but BE SURE to BENCH BLEED it before you put it in... I had a buddy that figured he'd hook up the master cylinder and just bleed it with it in the car... doesn't work.

 

[danieldick]

New master cylinder

I have a 72' Blazer that the idiot light came on for the brakes. I could take the pedal to the floor and then come up and all the brakes would then apply. I put a tru-torque master cylinder in and it fixed the problem.

If it can be seen, it can be hit. If it can be hit, it can be killed.
Armor theory

 

[rjfguitar]

Normal fluid flow to the rear brakes, both times I checked. My galvanized lines are almost new, I put new lines on my 14BFF when I installed it. The line that comes down from the body is original though.

I am also thinking master cylinder. I guess the chances of a prop valve malfunctioning is not common?

Ryan,
how do I bench bleed the cylinder?

Jake,
Read the dang post, yes I checked the fluid level.

 

[tucsonkfive]

I've known a couple of guys who had to replace the preportioning valve. They ain't cheap but might be worth splurging when it comes to brakes.

 

[rjfguitar]

What are symptoms of a bad prop valve?