Replacing a RABS Valve

I am not fully conversant with the RABS valve, though over the years I have had experience of g-valves, pressure limiting valves and load sensing valves. In all those systems the valve is an addition to a basic hydraulic circuit and I imagine the RABS valve is the same, an addition that limits the maximum braking effort of the rear brakes.

It is the master cylinder that produces the dual-circuit braking system with each circuit being separate from the other, though the split might be front/rear, which is the popular choice, it might be a diagonal split where each section of the master cylinder supplies one front and one diagonally opposite rear brake.

The reason is, you have a rear anti lock brake system. The anti lock valve is located on the frame just underneath the brake master. It is called a RABS valve. Almost impossible to bleed. But it can be done. A dealer has a tool that plugs into the RABS valve which activates the valve constantly moving the valve back and forth. This will then push all fluid and air out of your open bleeder screws in the rear.
I did'nt go to the dealer. i was too stubborn. My solution was to lift the rear of the truck and place on jack stands. Pinch off the rubber brake hoses on the 2 front brakes with a C-clamp or non marring vise grips, this will keep all fluid from going to front brakes. Next adjust the rear brake shoes by tightening the adjuster on the rear brake drums. Tighten the brakes on the rear until the brakes start to drag and the tires no longer spin freely by hand. Attach a bleeder hose to the bleeder screw on the RABS valve, place open end of hose into a jar or canister of brake fluid, so as not to draw in any air. Open the bleeder screw. Start the vehicle up, put it in gear, and let the rear tires spin. (I got up to 25mph on my speedometer) Step on the brake while it is in gear and the tires are spinning. This will activate the RABS valve and cause the air in the RABS valve to bleed. Do this several times. Put vehicle in park, shut off engine, and close the bleeder on the RABS valve. Attach bleeder hose to right rear of the truck, place open end of hose in a canister or jar of brake fluid so no air gets in and open the bleeder screw. Start the vehicle up, put it in gear, and let the rear wheels spin freely. As the wheels spin, you press your foot on the brake pedal, this will activate the RABS valve, and effectively bleed the brakes. Do this a dozen or so times, tighten the bleeder screw and do the other side. Remove clamps from front brake hoses and you will be go to go. All this may seem a bit extreme, but it is the only effective way to bleed a Rear Anti Lock Brake System on an early Ford. All the steps I laid out are necessary. You cannot skip one. The reason why the rear has to be in the air, is that there is a sensor mounted to the rear differential that senses wheel spin(or axle spin), this goes directly to the RABS valve and tells it that the tires are moving at a certain speed, and to activate the Rear Anti Lock Brakes when the brake pedal is depressed. It will not activate if it does not sense movement. The reason for pinching off the front brake lines, is that there are needle valves in the master cylinder and they will send too much fluid to the front calipers, and stifle or hinder the amount of fluid needed to go to the rabs valve and ultimately the rear wheel cylinders. It seems like a lot, and it is, but I did it and it works. Good luck

Your vehicle is equipped with antilock brakes. It either has a "Rear Antilock Brake System" (RABS) or it is equipped with "4 Wheel Anti-Lock" (4WAL).

Some units use a pressure regulating valve that screws into the rear port on the master cylinder.
All units built in 1995 have lines that go to either the Hydraulic Control Unit (HCU) or to the RABS Valve. However, that vehicle does not use a conventional proportioning valve, so I am not sure what to tell you.

rear antilock braking system=R.A.B.S.and cheers from U.S.A

the brake line goes from the rabs valve to a rubber hose near the rear end. It is ran behind the fuel tank.

SOUNDS LIKE IT IS A BLEEDING NIPPLE FOR BLEEDING BRAKE SYSTEM.

The problem may be that the master cylinder needs to be bench bled,there is most likely air trapped in the piston of the master cylinder.The problem comes from the piston not being fully actuated when connected to the pedal assembly.A vacuum bleeder will generally pull it out.

I would POWER BLEED the brake system. Hope this helps

Start from right rear, then, left rear, right front, left front. Fill master cylinder. Have helper sit in car, have helper hold brake pedal down. open bleed screw. fluid and air comes out. close screw. release brake pedal. Continue until no air comes out. Move to next wheel. Keep an eye on master cylinder fluid level after each wheel.

I would strongly recommend checking your trucks R.A.B.S. (Rear Antilock Brake System) valve . It is located on the left frame rail just under where your left foot would rest . They can leak internally and exhibit the problems you are describing (loss of pedal , with no fluid loss) .
It is highly unlikely that a power booster would cause this , as a failed booster will show itself in these ways . 1) a hissing sound when you apply the brakes (indicates a vacumm leak) 2) rough engine idle/stalling when brakes applied (also indicates a vacumm leak) or 3) No power assist (brake pedal hard to push) .
If you do discover your hydraulic problem is in your RABS valve , don't forget to bleed it ,(there is a bleeder valve on it) and the rear brakes again after you replace it .
Hope this helps
Doug