OK guys.. ran into a strange one at work today.. thought I'd pass on this information.. it might help one of you one of these days.

We had a 1996 Ford Explorer Sport... Rear wheel drive, manual transmission, four wheel ABS.. Anyways we did lower ball joints and rear brakes to it, and on the test drive noticed the ABS was kicking on at low speeds, even though no wheels were locking up.

Talked to the customer and they admitted it's been doing this since before the work we did, and authorized us to check it out.

Our scanner (genisys) would pull ABS codes (although none were stored) but would not display any ABS information (Manufacturer information not available), so we were at a bit of a loss as to which wheel was causing this.

We found a TSB describing this exact condition, and blaming it on corroded wheel speed sensors, so we replaced the rear diff. sensor due to it's cheapness but that did not help.

Today sold both front sensors (this is not built into the hub, but is seperate because of it being rear wheel drive)... and after installing them the problem was STILL THERE! ARRGGH...

Anyways, like I said based on the symptoms, I felt I could eliminate any wiring or module issues.. no codes and only slow speed operation while applying the brakes. well it just didn't make any sense.

I noticed the front brakes were brand spankin' new.. pads/rotors/calipers so I went through the glove box looking for receipts, hoping to find more clues. I found a receipt for the front brake work at another one of our locations but out of town.. it was all done less than 1,000 miles and three weeks prior, but at least it gave me a good, and cheap way, to replace the rotors (under warranty) as we were teethering on upsetting a very good and loyal customer at this point.

I replaced both front rotors, and PROBLEM SOLVED!

After all was said and done I compared the two "old" rotors side by side, and the tone-ring on one was pressed on about 1/8" further than the other.. in other words it had 1/8" more gap between the ring and the ABS sensor, probably just far enough to cause an intermittant cut-out.

I had closely inspected the ring on the rotors when I had them off doing the front speed sensors, but did not notice any bends or chips or anything out of the ordinary at that time, but then again I didn't compare them side-by-side either.

Needless to say, the customer was very happy to have the problem repaired even though he had to replace a few parts that weren't necessarily bad. We got kind of lucky on this one.. but we were also honest with him as far as his responsibility to buying these parts before-hand.

Anyways.. before you condemn these front speed sensors, take a real close look at the rotors!

 

Good job!
Nice to hear of a good outcome every now and then.

 

it was like you were nancy drew trying to solve a murder.

great outcome.

i usually look at the rotors i took off and compare them to the new part for things like this.

never found a difference but thanks to you i will keep looking close before i put new part on.

 

aha! this would explain why my truck is doing this after two new rotors!!!!!!! Now I know what I need to fix! thanks MazdaRangerGuy

 

This is an issue I am dealing with at this moment also. I had to change the studs on my rotors, so I had to remove the ring and reinstall. I have taken them off 3 times, but still do not have at least one of them in the right place. I haven't found any measurements saying they have to be so far off the sensor magnet, but if anyone happens to run across it, please let me know...

 

The rings on the new (correct) rotors were positioned about 1/8th of a inch ABOVE the hub (with the rotor on the floor with studs pointing towards the ground).

The one bad rotor had the ring pressed too far on... with the ring about 1/8th of an inch below the hub lip.

Typically, air gap on these types of sensors is about 0.030".