rear antilock brake question

[mikeinpa]

I did a search and did not find what I was looking for.

I remember a post on this board about rear antilock brakes not working and there being a sensor on the rear brakes that detects when the brakes are about to lock.

Can someone tell me (pics would be even better) where this sensor is located exactly and what I should be checking for?

My problem is that I do not get any antilock braking. I do not get a light on my dash, it comes on when turning the ignition then goes off as it should.

 

[section525]

Here it is on my '99. I'm sure its in the same place on yours. The bolt head and the plate are the only things you need to remove. The sensor will slide right out. It's usually dirty and/or needs to be replaced. I believe they're a pretty cheap part. Good luck!

 

[mikeinpa]

Thanks for the great pic.

Hmmm...I thought it would have been mounted on or near the rotor but your pic shows it mounted to the top of the rear diff.

thanks again.

 

[MattHarrell]

Yeah, check the top of the rear diff. There's a wire coming out of the sensor so it's not too hard to find. I forget how expensive the part was but I thought it was pretty cheap at the time.

Why do you expect the light to come on? It should only be coming on when there's a fault somewhere. In my particular case I have to replace the ABS computer under the dash if I can only figure out how to get it out of there without pulling the whole dash off.

 

[mikeinpa]

I figured the light would come on because the antilocks dont seem to be functioning. I remembered someone posting about cleaning this sensor so I figured it would be a easy/cheap place to start. The light and fuses are fine so time to dig deeper. I hope its not the abs controller as it seems is your case.

Any suggestions on what to use to clean it? contact cleaner? alcohol?

also is there any risk of really messing something up if I mess with this sensor? I dont need to make a small problem a big one right now

 

[JDraper]

With RABS there is another condition that can cause the RABS to malfunction, but it is usually accompanied by a light on the dash. If the brake fluid absorbs too much water, it changes the density of the fluid, which fools the system into thinking there is not enough brake pressure. This in turn shuts off the RABS. I had that happen to my old '92. A complete system flush with new fluid fixed the problem, but it took a couple of days after the flush for the RABS to work again because the module is on a dead end brake line, and it took some time for the new fluid to mix with the old and increase the density.

It's just a thought.....

 

[mikeinpa]

good point and thanks. This truck was owned by my wifes grandfather who lived on coastal waters the entire time he owned it bu I have had the front brake lines replaced> Is it safe to assume the had to replace all the brake fluid when they did this job?

 

[MattHarrell]

Sounds like he doesn't even have a light on his dash, though

In my case the engine codes do say the computer has issues. Jeff - got an experience in removing that computer? I picked up another one from a parted out Explorer I was going to try and I think I've found it (to the left of the ash tray) but I don't see how that part comes out. My Haynes manual isn't useful for this

 

[JDraper]

Originally posted by mikeinpa
good point and thanks. This truck was owned by my wifes grandfather who lived on coastal waters the entire time he owned it bu I have had the front brake lines replaced> Is it safe to assume the had to replace all the brake fluid when they did this job?

Nope. You don't have to replace all the brake fluid when you do a line. It can be done with just a little fluid loss. With a truck that old and no know history on the age of the brake fluid, I would have it changed. Monro or Midas will do a power flush for under $30. Money well spent in my book, whether it's the problem or not.

In my case the engine codes do say the computer has issues. Jeff - got an experience in removing that computer? I picked up another one from a parted out Explorer I was going to try and I think I've found it (to the left of the ash tray) but I don't see how that part comes out. My Haynes manual isn't useful for this

Nope, haven't had to remove a computer yet in an X, but in other vehicles, it's not hard to get out. Usually held in with Torx head bolts, but don't know if that's true with the X. If I remember correctly, the computer in my '92 was in the right side kick panel, but I know Ford has moved them around over the years. I haven't looked for it yet in my '01. Check one of the websites for the aftermarket chips. One of them has the locations for all the different years, it might be Hypertech.

 

[MattHarrell]

Actually, I was referring to the ABS computer and not the engine computer. The engine computer is behind the passenger kickpanel. Oh well

Mike,
Exactly what problem are you having? It sounds like you don't have a light on. Are you just trying to verify that it does work?

 

[mikeinpa]

ok...let me see if I can explain.

My X came with factory rear antilock brakes. When turning the ignition key all the warning indicators come on then go out (as they should). When driving I have no warning lights lit, and everything seems fine. The problem is that in rain or snow the antilocks dont "oscillate"...they just lock up the rear wheels causing it to skid.

The fuse is ok and so is the "idiot" warning light on the dash (since it lights).

It just doesnt stop worth a $h!t in rain or snow.

I was thinking the sensor might be a place to start. I tried to get under there today and its a real PITA. I will have to try again after removing the spare tire and when it gets a little warmer outside.

 

[AlaskanJack]

Isn't the ABS module in the drivers side rear jack compartment on the 91's? If not then I've got an unknown box in there with a red indicator light. I almost sh&t myself when I first found it thinking it was a keyless entry module. That was short lived when I noticed the red indicator light and remembered that the ABS module had one.

 

[MattHarrell]

AlaskanJack,
Interesting, I'll look. I'm pretty sure my Haynes manual showed me the computer thing under the dash near the ash tray. I'll check again when I figure out where I put the manual. I got the part from someone parting out explorers and it sure looks like that piece under there that I can see - I just can't figure out how to easily get it out. I don't remember anything back in my jack compartment with a red light on it

Mike,
I understand what you're talking about - mine seem pretty bad too when the back is unloaded. I have felt them pulse, though, when I was transporting 1 ton of rock in the bed and I think I've felt them too in the snow when I've got the 300lbs of sand back there. I think when the differential sensor or computer goes bad the light on the dash should light up. Since they are rear drum brakes anyway I just don't worry about it and assume they are ABS for when you tow heavy loads

 

[TPLYNCH]

The module in the rear should be your 4x4 relay.

 

[AlaskanJack]

Oh I see, well guess I was wrong. Out of the 3 Explorers I own the 91 is the only one with just rear anti-lock and it is the only one with the module in the rear compartment. Made sense to me.

Oh well disregard every thing after hello.

 

[jar2187]

I have a 92 Eddie Bauer, my manual has that it came with Rear abs, however the light on the dash doesnt come on,(neither does the brake warning light, maybe there connected). So with so investigation i took the trim panel off the dash to change both bulbs. Come to find out where the rear anitlock light should be, theres nothing there. Can see straight back there were the socket and light should come through the slot. Puzzles me. Maybe it was taken out. (couldnt get to the brake warning light because there wasnt enough slack in the tach and speedo wires, just found out how to get to it, by unplugging the the speed sensor cable from the tranny but havent done it yet). The brake lines from both rear drums go to the top on the pumkin and i can feel some type of connector that connects them and then goes into the pumkin but cant see what it is. Is this the ABS sensor? Any other way to tell if I have abs?

 

[Mike_H]

Originally posted by mikeinpa
The problem is that in rain or snow the antilocks dont "oscillate"...they just lock up the rear wheels causing it to skid.

Is it both tires that lock up or just one. One tire locking with rabs is normal. Even if you have 4 wheel abs it is common to have one rear lock on you becase it is only a 3 channel system that is why the sensor is on the pumpkin not on the rotor or drum.

 

[MattHarrell]

I think all 91 and 92's came with rear ABS but I'm not positive if there was an option to get rid of it. If you feel a pair of wires going into a thing screwed down to the top of the pumpkin then this is the rear ABS sensor. I'm sure there's a picture somewhere on the board but I don't know where.

Personally I would get one of the dash lights and stick it in the socket and see if you can get it to light up briefly when you start it. It's possible that the previous owner had a fault in the system (sensor, computer, whatever) and got tired of seeing the light.

 

[jar2187]

The socket is not even there, theres nothing, each warning light is boxed off it its own section and theres nothing in the section for the rear antilock light

 

[MattHarrell]

Hmm, strange. I've never actually had to replace those bulbs so I don't know what the socket looks like. It's possible you don't. I would check for the sensor on the pumpkin (look for wires going to it) and if you're really concerned then you can look for the ABS computer. Mine is gold colored and is located to the left of the cigarette lighter. You can see it up under the dash or when you pull the ash tray out.