I have a 1999 f150 4x4 with 4 wheel abs, disc front drum rear. The truck has 50k miles. I have been experiencing what feels like the ABS system kicking in at very low speeds. It seems to happen when I am backing out of the drive way, or pulling into the gas pump....stopping gently at 5 or 10 mph. I have changed the rear abs sensor (the old one was gummed up....but no improvement with the new one). My ABS light is not on, other than when you start the truck to show that the bulb works. I have changed the pads, rotors, brake fluid and rear shoes and adjuster levers...aside from other obvious improvements, no improvement in this problem. Anyone out there with experience in this area or insight would sure be appreciated....thanks!

 

is rain involved at all? after rainfall my abs goes off from wet discs/pads

 

While I know it has happened when it is not raining....I do think it is worse when it is raining/wet or mornings with heavy dew. Interesting thought...I would also say it seems to slowly be getting worse....

 

Ok, so here is another clue to this problem....maybe it will help you figure this out....because it sure has me stumped...

The frequency of occurence is increasing. It happens in reverse as well as going forward. It generally happens at 3 to 5 mph. It happens with reasonably gentle pedal pressure. Increasing foot pressure will not help, once it occurs, however removing your foot and stomping on the pedal does....

So here is a recent example: I was in traffic, at a stop light behind some cars, the car infront of me pulled forward....so did I. As I stepped on the brakes hte pedal dropped a bit, it sounded like abs kicked in, but the truck kept moving forward...I pressed harder...truck didn't stop....the wife yells at me... I released the brakes and stepped on the pedal hard....we stopped quickly....I yelled at the wife....anyway, you get the idea!!!!

does this make the light go on for anyone?.....

Thanks for thinking about this anyway!!!!

 

Normally it does not because, it thinks 1 of you wheels has locked up. Does it pull to one side or the other when this happens? If so, the side it pulls to is probably ok and the other side is dumping pressure. This is usually caused by a weak sensor or a chipped exciter (tone ring). A close visual inspection of the tone rings will be required. 2 voltmeters would be helpful to tap the signals comming from the front sensors while driving about 3 mph in a stright line. They should read nearly the same, if they do, its probably a rear sensor (tone ring) problem.

 

Thanks for your reply. What you say makes sense to me. It does not pull, that I have noticed. Although I will pay a little more attention next time it happens. So, if it is the tone ring in the rear how to I inspect it?. Do I pop the cover off the differential?...and more importantly, is it a big job to replace the rear tone ring?

With regard to the front, how do I see the tone rings and what am I looking for as far as a problem...a chip? Also, I am embarrassed to say, I am not sure where the front sensors are exactly located located on a 4wd?....

I appreciate you help because this one sure has me stumped!

 

Your problem is more than likely related to one of the front wheel speed sensors. I had this problem on mine around 50K miles also. It was the exact same problem, pretty scary when you are in heavy traffice. The front wheel speed sensors are mounted to the back of the spindles, you can trace the cable back up under the hood. They are fairly cheap, and very easy to fix. If you need any more help please feel free to give me a shout.

 

What your experiencing with your truck is happening to mine as well. I've took it to a Ford Dealership and they couldn't find a code in the system for it, so they don't work on it. Please find a cure for the trucks!

 

Horseman, I would find a new dealer if I were you, there are a lot of faults that do not generate codes.

 

I think it is the speed sensors, or the abs ring on the front rotors. If they are not runnig true the speed sensors will read wheel speed wrong and cause the ABS system to go crazy. If you know somebody with an Snap-On scan tool you can look at the abs data stream and find out what is going on. I had the same problem on my 97 explorer. The sensor rings were out of round. had to replace the front rotors.

 

I figured I'd give you guys an update....being the procastinator that I am I have been living with the abs problem as described ...but finally decided to get after it...I think much of the advice given has been correct and that my problem is a front sensor ....I thought I'd just change both, but turns out they cost $180 a piece....so I brought in my truck to a local dealer to have them hook in and do some readings while driving....turns out it is the left front sensor that is bad....but then they said, don't be surprised if you have to do the right one too!....glad I paid for that diagnosis!!! anyway I am waiting for the part to come in...apparently it is a common problem and if successful I will post the process on how to change one of these animals..... by the way, in the few months since I've had this problem, I have noticed significantly more brake dust on the right wheel....

 

Ok, the fix is in and it works! I changed the left speed sensor and the problem is solved. Changing the speed sensor was simple, the part came with directions from motorcraft, the process was simple...pull the tire, caliper, caliper mounting bracket,rotor and dust shield ...then, 1 allen screw and the sensor pulls out by hand.....I got to this part in about 10 minutes as I had taken my rotors off before and used anti sieze compound on the hub....now here is where I hit a snag...when i pulled the sensor it was stuck and when it finally came out, the plastic sleeve stuck in the hole....I used an ez out to get part of it and the rest with a pick and needle nose pliers.....it was a pain...but after about a 1/2 hour I got it out...with out dropping a bunch of crud in the hole.....

I think if the next one goes, i'd try a little liquid wrench on the base of the sensor....

 

I have the same problem with my 1997 Ford Expedition 4x4. IT's at the dealership right now. They told me I would probably have to replace my rear sensors and it would cost over $350. I have to drive for four hours tomorrow. Is there any way to somehow turn off the abs so that the truck does not lunge forward like you described, or is the only way to replace the sensors? Did you turn yours off or did the brakes continue to do that for the months you didn't get it fixed? and did it affect your rotors or brake pads if so?

 

I would like to ask the same question. How do you truly disable abs? It doesn't seem as simple as pulling a fuse. If it is, which fuse? I want to make sure abs is completely non-functional so that I can troubleshoot a brake problem and eliminate the abs electronics as a cause.

 

I was having the same experience with my wifes Windstar. After living with it for several months, I noticed that the gap between the sensor and the ring was greater on one wheel than the other three wheels. I was able to tap the sensor in closer to the ring.......Problem solved. Dave C.