ABS Problem on a 1991 F-150

make sure you are traveling at above 35 mph, those old ford systems didnt allow the antil lock to kick in until it sees your going at least that fast, and on ice if your rear end isnt trying to become your front end, sliding sideways, then it is most likely working properly, and you just dont have enough traction with the tires to make a difference when the brakes rapidly set and release.

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You do realize that it only has rear ABS
Bob

Yes Bob,
I realize that it only has rear ABS. Still, none the less, it doesnt work
and the computer doesnt see it. Any ideas?
Dennis
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Are you sure the rear wheels are actually locking up, or could it be that
just the fronts are sliding? I will admit to repairing a LOT of Ford trucks
with rear ABS and have never run into a Ford or any other make for that
matter that just refused to work without turning on a malfunction indicator
light.
Bob

Bob,
At first I thought that too, because by rear brakes were out of
adjustment. But I had them adjusted and I went and tried to skid them on ice
and they locked up. No ABS. I would have felt the ABS working too I think or
at least heard it. Im lost.
Dennis
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If the light goes out when the engine starts, then, the
electronics is working properly. It is most likely that
your rear brakes are not locking. Ford truck brakes of that
vintage are heavily biased to the front which means the
fronts will usually lock first. One problem that you may
look for is frozen rear wheel cylinders which is common with
them. Try pulling the ABS fuse and attempt to lock the
wheels. I suspect you won't be able to lock them. If not,
just replace the wheel cylinders. Have the drums turned and
install good shoes at the same time.

From my own testing, anti-lock brakes are not very effective on ice.
Apparently there's not enough traction to get the wheel spinning again after
the brake release. You may want to try testing on a less slippery surface
such as gravels or a wet road.

If there is any drag at all on the wheels, you may want to loosen your brake
adjustment slightly.

If the ABS kicks in, the rear of the truck should not skid to the side (on
a level surface). You will normally feel the pedal pulsing too.

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