No rear brake pressure after wheel cylinders replaced?

[Dr.Doug]

I replaced both rear wheel cylinders. When I attempted to bleed the rear brakes, there was no brake fluid or pressure at both rear sides.

This is a 1991 with rear ABS only.

Please advise why this is happening and how to fix it.

Thank you, Doug

 

[Adam Berger]

This may or may not help you. I think there may be a proportioning valve in the master cylinder. This valve is there in case of a failure in either end of the car (front or rear). Upon failure the valve will move forward or back to block off the end with no pressure, allowing some sort of braking. Again, i'm not sure if this will help. I don't even know if Explorer's have this.

 

[mrboyle]

Check your ABS valve. They are famous for rusting shut, blocking the flow of fluid to the rear brakes.

 

[Dr.Doug]

Where here is the fix.

I started the vehicle which gave vacuum to the power brake booster which provided fluid to the rear for bleeding. When the vehicle was shut down and the vacuum was lost, it was again difficult to get fluid from the rear.

Is this normal? I understand that the rear gets much less pressure than the front but this seems a little excessive. Braking has been fine.

Again, this is a 1991 with REAR ONLY antilocks.

Doug Thoughts welcome.

 

[Dr.Doug]

Well, its not fixed.

I don't see a pressure differential valve. Does the RABS valve serve as this?

The brake pedal is firm at first with good braking. The next two inches of brake travel there is not much change in braking. The next inch the rear brakes kick in and lock up if on a loose surface.

Is it possible that when I bled the system the RABS valve got stuck reducing brake flow to the rear. Now when I place extra brake pedal pressure the flow gets to the rear brakes and lock them?

Please advise

 

[mrboyle]

The symptoms you described are all related to a bad ABS valve.

 

[Dr.Doug]

Mr. Boyle,

Is it you thoughts that the RABS valve could be bad even though the idiot lights for the ABS or the Brake have not illuminated?

In addition, does the 91 have a traditional brake proportioning valve or is it incorporated into the RABS valve?

All of this started when I replaced the rear drums, brakes, new rear brake springs and both rear brake cylinders.

Yes, the springs and shoes are installed correctly and the system was bled properly.

Thank you for your response.

Doug

 

[mrboyle]

The I have never seen the RABS valve turn on the ABS light. Even when mine was rusted shut and not working at all. The valve also serves as a perportioning valve, to a point. Your problems may not have started when you did the work, they just became appearent.

 

[Dr.Doug]

Last question.

Is the RABS valve a dealer only part. I thought that I read a thread regarding a rebuilt one.

Thank you for your assistance.

 

[mrboyle]

I got mine from NAPA. It is a rebuilt unit, so there will be a core charge, but its no big deal if you take your valve in with you when you purchace the valve.

 

[Dr.Doug]

RABS replaced and all appears well. I do notice that in a light panic stop the rear wheels lock-up before the fronts. The ABS kicks in but I don't think that the rear brakes should have so much stopping power. In addition, the rear rims feel very warm from normal braking. In addition, the passenger side feels a little warmer than the driver's side.

What does every one think?

Thank you, Doug

 

[mrboyle]

Have you tried bleading the fronts since you got the rears fixed? You never know! The only other thing I can think of is that you possibly have the rear brakes adjusted too tight.

 

[Dr.Doug]

Yes, all lines were bled to include the master cylinder. I wanted ALL of the old fluid out.

Lets review:

-New calipers and brakes (New pins and lubed)
-New rear drums and shoes (New spring kit)
-New RABS valve (rebuilt)
-New rear wheel cylinders
-New rear brake line from the RABS valve to rear split
-Existing master cylinder bled
-All four corners bled, starting with pass rear, driv rear,
pass front and driv front.
-No brake fluid leaks
-No rear end fluid leaks onto shoes

I drove 300 miles today and the brakes feel good and firm. (Maybe a little too firm.) It is possible, maybe, that the rear brakes may be adjusted too tight. (The rear wheels do spin freely when the brakes are not engaged.)

QUESTION:

I don't see a proportioning valve. Is it part of the master cylinder?

What is the proper adjustment of the rear brakes?

Thank you.

Doug




Have you tried bleading the fronts since you got the rears fixed? You never know! The only other thing I can think of is that you possibly have the rear brakes adjusted too tight.

 

[mrboyle]

If the brakes feel a little firmer than your use to, it is possible the rears were over tightened, but after a 300 mile trip they should have worn enough to eliminate that problem. I currently don't have any other clues as to what the problem could be.

 

[james t]

basically, just drive it for a week before you try to trouble-shoot it. sometimes new drum components can be a little "grabby" when new. drive it for a while, let the shoes seat and bed in to the new drums. let everything get "cured". i wouldnt worry about the excess heat from the rears, as this could just be normal during the seating/curing process. if it is still grabby in the rear after a week, then i dont know what to tell you. strange problem you have, as i have only had the problem once with a Ch*vy with new rear drums, and it went away after the first day...