Hello all,

I'm posting this to help others.

I have seen numerous posts on the net complaining that after doing a front brake job, the ABS activate when almost stopped.

In my case I worked on a truck that I was not familiar with and was not aware if the ABS was working prior to doing the brake job.

I installed pads, right front rotor, and right front caliper. The RF rotor was scored bad and had not been replaced during a prior brake change, also the RF caliper was sticking.

I mucked with this truck for two years throwing random parts at it.
I replaced the ABS sensors, then the other rotor with no luck.

I finally bought the Autoenginuity scan tool, so that I could see wheel speed sensor data. It looked like the RF dropped out before the rear and LF.

The rotors on this truck have a stamped steel tone ring on the back, around the bearing boss. During storage and shipping, when the rotors are stacked flat, the studs from the rotor below can bend the tone ring and cause it to run out. This run out causes a air gap that is too great for a accurate sensor reading.

To inspect for run out, raise the front wheel up and observe the tone ring while spinning the wheel. If it has run out at the tone ring on the back, replace the rotor. There will be no question, run out will be clearly viable.

I replaced the RF rotor, and now all is good with our ABS.

1996 Ford Ranger Extended Cab, 4.0 OHV, 4WABS, 2wd

Robert Wynkoop