weird brake problem????

[6.2Blazer]

I have a weird brake problem that just started on my K5.

First of all, I haven't had any time to look at it further but I was hoping to get some helpful leads as to where to start.

This weekend I had it on the hoist at work (which I use all of the time) grooving my tires. When I went to pull the truck out the red "brake" light came on and the pedal felt slightly "weird", but didn't go to the floor or feel overly mushy. Everything was fine when I pulled it into the garage.

I went out on the snow and ice covered parking lot and tried the brakes out......the fronts easily locked up but the rears did not, even on ice, so there is little or no braking on the rear. The brake light stays on constantly.

The fluid level in the reservoir is fine and I did not see any obvious external fluid leaks.

It's an '90 K5, 60/14FF, rear discs........I've been running the same setup for several years with no issues.

Any thoughts?

 

[mtnman210]

How about your booster? that was the source of all my brake problems. The M/C had leaked into the booster ruining it and caused a nice vacume leak. I could bleed the lines over and over and everything would seem fine. But after a few times driving I'd loose the pedal pressure and braking power until I replaced the booster itself.

Just my 2cents

 

[diesel4me]

Master cylinder??

If your sure you dont have a leak in a hard line or rubber brake hose,and the wheel cylinders are not leaking,you might have a bad seal in the master cylinder for the rear brakes,my 82 K20 has been leaking brake fluid out of the rear of the master cylinder,where it joins the hydroboost,and my brake light wont stay off either--
it eventually will empty the resivouir,and it allows air in the rear brakes--its possible the seal is leaking enough on yours to let air into the system,but not leak out--might be the proportioning valve also,but they dont go bad too often...I'd check real close all the metal lines and connections,a slight leak might go undetected,but allow air to sneak in--in my area,rusted brake lines are the usual cause....

 

[JK5]

I have a weird brake problem that just started on my K5.

First of all, I haven't had any time to look at it further but I was hoping to get some helpful leads as to where to start.

This weekend I had it on the hoist at work (which I use all of the time) grooving my tires. When I went to pull the truck out the red "brake" light came on and the pedal felt slightly "weird", but didn't go to the floor or feel overly mushy. Everything was fine when I pulled it into the garage.

I went out on the snow and ice covered parking lot and tried the brakes out......the fronts easily locked up but the rears did not, even on ice, so there is little or no braking on the rear. The brake light stays on constantly.

The fluid level in the reservoir is fine and I did not see any obvious external fluid leaks.

It's an '90 K5, 60/14FF, rear discs........I've been running the same setup for several years with no issues.

Any thoughts?

Stuck proportioning valve??

I have to tap on the black truck's valve with a hammer from time to time...

 

[6.2Blazer]

I will look over all the lines real carefully. It just sounds odd that I would have no back brakes at all with just a small leak, yet the front brakes and pedal feels fine.

The booster should be fine, if it was the problem I would think it would also effect the front brakes and pedal feel, right???

If I don't find any leaks than I will tap on the proportioning valve and see what happens.

 

[88sub4x4]

I'd have to say master. When mine went the back circiut went out, but the front stayed fine.

 

[6.2Blazer]

I'd have to say master. When mine went the back circiut went out, but the front stayed fine.

Did it just go out suddenly, or did it act up over time?

 

[88sub4x4]

I guess it happened over time. It just took a while to notice it. I usually drive pretty easy, but when I needed to stop hard one day, I noticed my rear brakes worked for a second, and then weren't working until I pumped the pedal again. When they weren't working the red brake light came on. I found that if I sat stopped, and applied the brake really hard and held it there a few seconds it would start to drop and the light would come on. The fluid that was supposed to go to the back, was leaking back into the master. I pulled the master apart, and the o-ring was cracked. I put a new master in (from the GM dealer I work at) and I will overhaul this one when I get a chance. The rebuild kit is about 20 bucks.