Brake/Rabs issue, no rear bleeding

[SirRea63l]

I replaced my rear drums on my 94 CCLB 4wd zf5 because they were worn way down and the driver side was dragging. I noticed one wheel cylinder had a slight leak so I decided to replace both of them as well. Everything went smooth on the pad and cylinder replacement. The driver side cylinder bled perfectly but the driver side is not.

It only bled a little and then stopped flowing air or fluid. It appears the RABS has sensed pressure loss and activated preventing the rear from getting any more fluid. This is what my research has led me to believe anyway. What I have not been able to do is get the RABS to release. The brakes on this truck have always been perfect, solid peddle, no sponginess so I don't believe there is any air in the RABS unit.

I have tried getting the drivers front to flow by bleeding it to relieve pressure on the RABS, no dice but it does pump solidly out of the front as expected.
I have both a vacuum bleeder and power bleeder, neither have helped.

I don't think there is a traditional proportioning valve on this truck and the few YouTube videos I have found are dealing with air in the master or RABS unit, I don't believe that is the issue here. Does anyone have a solution to getting the RABS to release so the fluid can flow as normal?

 

[gnathv]

Did you crack the bleeder screw on the RABs unit?

 

[SirRea63l]

Did you crack the bleeder screw on the RABs unit?

No, I have not touched the RABS, concerned about getting air in it.

 

[Nero]

You bleed the RABS just like you would the rest of the brakes. If you depress the brake while cracking it, air won't get in.

 

[SirRea63l]

You bleed the RABS just like you would the rest of the brakes. If you depress the brake while cracking it, air won't get in.

Will that release it so fluid flows to the rear? There should not be any air in it and I want to be sure before I crack the bleeder open. I would have thought bleeding the driver front would have done the same thing as releasing the pressure on the RABS. I would love to be wrong though.

 

[Nero]

It's possible. Hard to say. I'm thinking that something is causing the RABS valve to be stuck, so trying to bleed it may cause it to unstick.

 

[SirRea63l]

It's possible. Hard to say. I'm thinking that something is causing the RABS valve to be stuck, so trying to bleed it may cause it to unstick.

I will hook the pressure bleeder back up and give it a shot in a while.

 

[franklin2]

The RABS system is common to both rear brakes. Go to the other side that bled ok and try to bleed it again. If you still get fluid, then the RABS is not the problem.

 

[SirRea63l]

RABS bleeder is clogged, as expected. lol

Neither rear wheel will bleed, fluid is not being allowed to pass to the rear brakes.

Prior to replacing the rear wheel cylinders, the brakes were perfect except for the passenger shoes dragging from being worn down to the rivets. New shoes and cylinders in the rear, nothing was changed up front, the front bleeds fine but nothing out of the rear. The driver rear did bleed just fine initially but once the rear passenger was being bled, no fluid comes from the cylinder and now nothing comes from either rear cylinder.

I replaced one cylinder at a time, starting with the driver side. Fluid was slowly dripping from the lines on both sides while the cylinders were being replaced.

 

[Clb]

Try back bleeding it with the bleeder clear and cracked open, then closed....

 

[SirRea63l]

Try back bleeding it with the bleeder clear and cracked open, then closed...

Thanks, but which bleeder are you talking about?

 

[1mouse3]

Two ways I would go about it would be...

1- Open a bleeder and stuff a hose on it, with the other in a bottle of fluid higher than. Then pump up the brakes some, it should get a hair stiffer. You should see fluid dripping from the bleeder if it worked out.
2- Open a bleeder, then have someone push and hold the brakes. The close the bleeder, then repeat till you get fluid.
3- Could also do a mix of both holding your finger on the bleader, having someone pump the brakes till theres fluid.

 

[SirRea63l]

Two ways I would go about it would be...

1- Open a bleeder and stuff a hose on it, with the other in a bottle of fluid higher than. Then pump up the brakes some, it should get a hair stiffer. You should see fluid dripping from the bleeder if it worked out.
2- Open a bleeder, then have someone push and hold the brakes. The close the bleeder, then repeat till you get fluid.
3- Could also do a mix of both holding your finger on the bleader, having someone pump the brakes till theres fluid.

That is how we bled them initially. The brake pedal is now hard, not pushing down at all. I can release the pressure on the front caliper and the pedal will be able to push one time, but it is only pumping fluid to the front, the rear is locked out. That is the problem, no fluid will flow to the rear, either rear.

The FSM shows a proportioning valve in the master cylinder (if equipped), but no real information on it or which vehicles are equipped with it. The FSM aslo says there are proper bleeding instructions in 06-00 in numerous places in the Brakes section but the bleeding procedure isn't there.

I have disconnected the battery, will let it sit overnight. It is over 100 degrees out and I am old.

 

[Clb]

Back bleed from the/ each rear wheel cyl.to and thru the rabs.
You are trying to reset the poppet valve that stops flow.
Also helps clear foulef bleeders if it's not just mud in the outer port/hole/ opening.

Fwiw
There was a recall on the proportioning valve @THE mc end ...

 

[SirRea63l]

Back bleed from the/ each rear wheel cyl.to and thru the rabs.
You are trying to reset the poppet valve that stops flow.
Also helps clear foulef bleeders if it's not just mud in the outer port/hole/ opening.

Fwiw
There was a recall on the proportioning valve @THE mc end ...

Thanks, that makes sense. I just need to figure out how to put enough pressure on it without using an air hose to blow the fluid back. lol

The only bleeder that is stuck is the RABS one. I would take it off and clean it properly but then there is the concern of it getting air in it, which I understand is a huge pain to bleed out.