1998 F150 4X4 - ABS question

It seems like my ABS has stopped working. I'm getting lockup in the rear, one or the other, or both rear wheels tend to want to lock up when braking. There is no heat build up in the brakes so I assume that the brakes are not dragging all the time, the ABS light comes on for a few seconds on start up as normal and does not stay on at any time. I thought at first that it could be the emergency brake not releasing but again, no heat build up like a dragging brake shoe, also no smell of burning brakes. Is there an ABS module or something that can fail without turning on the light? Thanks.

Del.

PS. Please be kind, I haven't done a brake job in at least 15 years.

Reply to
Del
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I plan on taking it into the dealer for repair but would like a bit of info before I go in. Thanks.

Del.

Del wrote:

Reply to
Del

On Sat, 06 Oct 2007 17:11:12 +0000, Del rearranged some electrons to say:

When your wheels lock up, can you feel the ABS pulsing the brake pedal?

Rear ABS is disabled when you are in 4 wheel drive. Are you in 4 wheel drive?

What condition are the shoes and return springs? What condition are the wheel cylinders?

Reply to
david

I believe your truck has 3-channel ABS. If true, this means that the rear brakes are controlled as one while the front brakes are controlled individually. For ABS to kick in on the rear, both wheels would have to lock.

4-channel systems will modulate each corner separately, and this would keep the rear wheels from locking. But with a 3-channel system, it is possible for one rear brake to lock and not have the ABS kick in because to modulate the brake that is locked would aslo modulate the brake on the other side that is doing its job, albeit on a lesser level. In an instance like this, I think the corrective action is to adjust the rear brakes so that they work together. It sounds like one brake is working better (sooner) than the other one, and it can lock before the other brake activates.

Reply to
Jeff Strickland

On Sun, 07 Oct 2007 01:05:59 +0000, Jeff Strickland rearranged some electrons to say:

98 F150 has rear ABS only.
Reply to
david

Okay.

To control each tire separately, there would need to be two brake pipes leading to the rear axle. If there is only one brake pipe -- hard line that carries brake fluid -- then both rear wheels would need to lock before the ABS kicks in.

If there are two brake pipes, then I do not know what the problem is. Sorry.

Reply to
Jeff Strickland

Are there sensors at each wheel in the rear-only ABS? If that's the case, both wheels may not need to lock to activate the ABS. One wheel lockup would trigger the ABS at both wheels. This is just a guess on my part, but it seems to me it would be more practical to trigger the ABS for a minimum of one wheel lockup.

Reply to
Matt Macchiarolo

I follow your logic, but I think it is flawed.

If one tire is locked but the other is not, if the ABS kicks in, then the unlocked tire will work even less than it is already working. That seems to me to be a serious problem. One does not want too much braking, but too little braking is as bad or worse. I agree that having both tires in a skid is bad, but having one brake work less so that the other does not skid is even worse. The point of ABS is to keep the back end from coming around, but if one of two tires is not skidding, the back end will remain controllable and ABS is not needed.

Reply to
Jeff Strickland

On Sun, 07 Oct 2007 16:12:26 +0000, Jeff Strickland rearranged some electrons to say:

The wheel speed sensor (singular, not plural) is picked up on the diff ring gear.

Reply to
david

That would require both wheels to lock before the ABS kicked in. This means the brakes are out of adjustment since one brake locks and the other does not.

Reply to
Jeff Strickland

On Sun, 07 Oct 2007 19:53:28 +0000, Jeff Strickland rearranged some electrons to say:

Quote from OP:

Sounds like it's not just one wheel.

Reply to
david

Gee do you think the surface the tires are on might play a role in that? I can give you a perfect adjustment, and if one wheel has less traction than the other, it is going to lock up. One tire with lower air pressure than the other is another scenario that would result in one wheel locking up.

Whitelightning

Reply to
Whitelightning

Is this the first year you have had the truck? Does this locking up of a wheel only occur the first few stops of a trip? If so, the likely cause is condensation build up in the brake drum over night will cause the mechanism to get sticky. The first time you stop, the brakes will grab, and one or both sides will lock up.

Since this is a mechanical lockup, and not a function of hydraulic pressure, the ABS can cycle the hydraulics all it wants and it won't unlock the stuck brake. Usually if it is an issue with condensation, it will clear up after the first few stops.

Reply to
Mike H

No, just the rear lock up.

No not in 4 wheel drive.

The brakes were done in July.

As far as I know they are in fine shape. That is what I'm getting looked at this coming weekend. I just do not have the time to do this myself.

Del.

Reply to
Del

No, I have had the truck for about eight years.

Yes and no, sometimes it lasts for about an hour and then just slowly clears up until I let it sit for an hour or so and then starts up again.

It does tend to do it more when the weather is damp/wet.

My problem is that it lasts more than just a few stops, if it is condensation build up, is there any way to stop the locking up? It can feel downright scary when you tap the brakes lightly and feel the rear end of the truck wanting to pass you.

Someone has suggested that it make be the self adjusters getting old and sticking, is this a possibility?

Thanks.

Del.

Reply to
Del

If the self adjusters where the issue you would have to opposite problem, low brake pedal and poor braking from the rear brakes. I wouldnt be too quick to rule out parking brake issue, especialy the cable going to the right side rear wheel. Thwen again it could be an issue with the brake linings themselves. I've seen cases where three linings were from one batch and the forth from a second batch causing issues like this. When it happens with disk pads you get pull one way cold, and the other way hot, sometimes quite severe.

Whitelightning

Reply to
Whitelightning

Sure, but if that was the case he would not be asking here what is wrong. Since there is a question, I'm assuming the road is flat and dry, or there would not be a question. I assume that people know that dirt on the ground can let one wheel skid before the other, therefore a complaint that one wheel skids before the other must mean the brakes need adjusting. Snow or ice can do the same thing, and I assume people know that as well.

The OP is concerned that his ABS might not be working because one tire or the other seems to skid. If the truck is operated on the street, and one tire skids before the other, the ABS is not going to work and since one tire skids, the problem is that the brakes need adjusting, OR the guy needs to understand that the roadway has dirt on it allowing one tire to skid. Either way, there is nothing wrong with the ABS.

Reply to
Jeff Strickland

Thanks, I guess I wait till next weekend to see what the dealer says the problem is.

Del.

Whitelightn> If the self adjusters where the issue you would have to opposite problem, > low brake

Reply to
Del

Flat paved road, dry or wet. It does seem to act up more on the wet road but I was thinking this was just because the road was wet and the tires did not grip as well. Relieved to hear it's probably not the ABS system, now all I want it to do is stop like it used to for the last eight years.

Del.

Jeff Strickland wrote:

Reply to
Del

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