Explorer ABS - how does it work? I'm trying to fix mine.

NMBRONCO77

MEMBER
FORD EXPLORER

1991 Explorer 4 door 4x4 168,000 miles My rear brakes stopped working. I could tell that only the fronts were stopping me. I thought maybe I had moisture in my brake fliud, and because it has been below 0 degrees here, I thought maybe the water had frozen my brake lines shut. I was only having this problem when it was real cold, but once the day got warmer the brakes worked just firne. So I figured that I would change the fliud out by giving the brakes a good bleed. I was not able to get ANY fliud to come out of the rears. I removed the brake lines from the wheel cylinders and the master cylinder and I was able to blow air through the lines from the wheel cylinders toward the Master cylinder, but not the other way ( from the master cylinder toward the wheel cylinders). My question is, is the ABS system, or some safety system shutting off the supply to the rears? Does it think that I blew a rear brake line and shut it off so I wouldn't loose all my fliud? I have put a new Master cylinder on it and the fronts bled just fine, but nothing out of the rears. Is there a one way valve that will allow air to pass back forward abut not front rearward? I really am baffled here. I need my wheels to get to work tomorrow. Is there something I can reset?
Pat

8 Replies

BACKYARDMECHANIC

MECHANIC
337 POSTS

Did you clear the code with the scanner after replacing the part? Also check the wiring going to and from the camshaft senor. There could be a break in the wiring which would still return a code as if the senor was defected. Hope this helps
Backyardmechanic?

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Monday, December 4th, 2006 AT 7:02 AM

TAURUSWHEEL

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718 POSTS

Did you happen to jack the rear of the car up one side at a time? Or was the car tilted in any way other then level? There's a valve in the rear lines that will go off-center when the car is not level and you attempt to bleed the rear brake lines on either side. This is not well-known because there is no direct mention of it, in those words, in the repair manuals. Ford or otherwise. No matter how hard you attempt to push the pedal, no fluid will pass or very little, next to none. If you're lucky the valve will re-center itself, if not it must be replaced. This is for ABS systems only. The car must be relatively level when you bleed the lines, preferably on a lift. It can be done with jack stands, but more work.

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Sunday, February 4th, 2007 AT 1:16 PM

NMBRONCO77

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Hi TW,

That is very interesting. I have never heard of anything like that before. But, too bad that is not my problem. The first sttempt at bleeding was done with the vehicle setting on the ground. When I jacked it up, it was with my floor jack under the pumpkin.
I think I have narrowed it down to, what I think is, the ABS valve unit that is mounted to the inside of the frame almost directly under the master cylinder.
But I don't know how that thing works. I have a 77Bronco that I know from one end to the other. It has a proportioning valve on it to control flow to the front and rear, but I think that this Exploder has it built into the master cylinder. Although I could be very wrong. A friend told me that the ABS unit was mounted on the rear end where the brake line comes from the front and tees out to the wheels. He was wrong. All that is there was a brass tee (or Y).
Does anyone know exactly what that unit is that is mounted to the frame? Is it ABS or is it a PRO valve? Whatever it is, how can I get fluid through it to the rears?

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Sunday, February 4th, 2007 AT 3:44 PM

MATHIASO

MECHANIC
1,209 POSTS

The first procedure to follow when there is an ABS fault is to carefull inspection of the system. Is the reservoir full of fluid?Is there a leak in the system?Is there a damage line or frosen caliper or frosen cylinder wheel? Is the proper fluid in the system and what is the fluid condition?Are the parking brake switch and brake pedal switch working and are they properly aligned?Are the tires installed the correct size for the vehicle and are they properly inflated.

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Sunday, February 4th, 2007 AT 5:05 PM

TAURUSWHEEL

MECHANIC
718 POSTS

77 bronco, that proportioning valve is controlled by weight distribution of the vehicle? It is controlled by a spring actuated lever? I know Ford wagons had pro valves attached to the master cylinder directly while sedans were usually mounted seperate from the master cylinder, Explorers I'm not sure. It could be the unit you're describing is the abs controlled hydraulic actuating device, the piece that does the actual brake pulsing during lockup? The hydraulic control unit I think it's called.