Rear brakes dont work

Ok i put my jeep on stands and placed the car in drive. While the wheels are spinning i am applying brakes and the wheels won't won't stop turning. The drums are adjusted correctly. i am pretty sure the rear bakes are just not getting enough hydrualic pressure because i can stop the wheel from turning with the parking breaks. The entire system is bled correctly. My question is how do i know if its the master cylinder or the boost pump? Do i just have to replace one and see if it fixed the problem? Any input on this would be great. thanks

What year? Got ABS?

Is the brake light coming on? That would indicate a major imbalance between the front and rear hydraulic circuits. You might have seized rear pistons, or it really isn't properly bled.

lawsoncl said:

What year? Got ABS?

Is the brake light coming on? That would indicate a major imbalance between the front and rear hydraulic circuits. You might have seized rear pistons, or it really isn't properly bled.

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Or you might have a malfunctioning or non-functioning ABS system, or you may beed to replace the combination/proportioning valve.

We really need to know more about your vehicle, and any repairs that may have already been attempted.

Its a 99 with a chy 8.25 rear. No abs. The only repair i did was to install new shoes. I bled the system and there is no air in the system. What is the proportioning valve and where is it located. With the drums off i hit the breaks and the pads move outwards which would indicate to me that the actuators on the drum work.

They may have moved out, but do the move out far enough to make a solid contact against the drum? I would go through and readjust them. Go out and make some stops in reverse, then adjust them again. No leaking wheel cylinders?

No leaks. They are already adjusted. Is it hard to believe that the master cylinder or the boost pump is bad?

I am experiencing this same problem in my 96', no abs. The parking brake light is on, which from my research indicates a difference in pressure between the front and rear lines. The strange thing is,the level of the brake fluid in the resevoir has increased. Front brakes work fine, and Ive checked all hard lines for damage, and couldnt find any problems. I haven't yet bled the system, as i don't yet have the proper tools. Would that be my next step? Or do i need to overhaul my combination valve and master cylinder?

Chances are the drums are not adjusted. How do you know they are adjusted as you claim? I'd double check them.:repair:

[email protected] said:

Its a 99 with a chy 8.25 rear. No abs. The only repair i did was to install new shoes. I bled the system and there is no air in the system. What is the proportioning valve and where is it located. With the drums off i hit the breaks and the pads move outwards which would indicate to me that the actuators on the drum work.

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I'm still thinking the brakes need to be adjusted, bled again, or possibly you installed the new brake shoes incorrectly (swapped front- back?).

It's the brake proportioning valve. . . I just had to go through this exact problem with my XJ which is non ABS. Have fun! It's a PITA.

1 Remove the brake sensor from the top of the valve.

2 Remove the screw cap from the front of the valve taking care not lose the spring in side the valve.

3 Reset the valve.

4 Reassemble the system.

5 Bleed the system using a vacuum bleeder.

Viola! you should be good to go now!

SBrad001 said:

It's the brake proportioning valve. . . I just had to go through this exact problem with my XJ which is non ABS. Have fun! It's a PITA.

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So your prop valve was stuck? Was the brake light on?

[email protected] said:

No leaks. They are already adjusted. Is it hard to believe that the master cylinder or the boost pump is bad?

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Adjust them tighter. If the wheel cylinders are pushing the shoes outward, the hydroulic system is functioning properly. The pedal should be pretty hard as well with the drums on, if the pedal is a little soft the rear brakes need adjusting. I believe the red BRAKE light would be on if the prop valve was the problem, plus if there was no hydroulic pressure getting to the rear wheels the wheel cylinders would not push the shoes outward as you describe.

Driving in reverse and jamming on the brakes isn't the best way to adjust them up either. Jack up the rear, leave the car in Neutral, and adjust them until there's significant resistance when you spin the wheel by hand, but not so tight that you can't manually spin the wheel. Do this on both sides and see how they work.

Also, when you replaced the shoes, did you replace or resurface the drums?

I just had this problem on my '99 with 112k on the clock. Turned out to be the wheel cylinders.

Dave