I have 1999 Ford Ranger XLT I recently did a brake job. New pads, rotors, bearing etc. The rotors looked exactly like the ones I had with the tone ring. Name brand part too. Now the anti-lock brakes kick-in for no reason. Doesn't do it all the time, weather, road conditions don't matter. Always happens under 5mph no ABS light comes on at all. I can go days with no issues, then like today, it was just annoying. I pulled the sensors, they look fine, cleaned the dirt and grease off them. I check the wheel make sure it didn't have any play in it. Before brake job, all was fine.

 

"Now the anti-lock brakes kick-in..."

So under 5MPH you feel a pulsing in the brake pedal, ABS is releasing pressure, that's all it can do, it can't apply pressure.

If brakes are acting "sticky" under 5MPH then one of the flexible hoses on one front wheel has a problem, it is acting as a valve because inside tube has separated.
That is something that can happen when working on front calipers.

If the pulsing is there then it could be the sensors are not reading tone ring(spinning part) below a certain RPM of the wheel, to the ABS that looks like wheel has locked up.
0 RPMs from a wheel sensor, with MPH showing on Speedo = locked up wheel

 

Wheel don't feel like it's locking or attempt too. I can be a a slow roll with light/medium pressure on the pedal. Then anti's kick in. Road is concrete and dry. Then it will be a few days no issues. Outside temp or humidity don't seem to matter.

 

Still not clear on the "....kick in" part.

ABS causes pulsing in the brake pedal, is that what you feel.

 

Kick-in as they operate as if I was sliding on ice.

 

So there IS pulsing?????

If you don't feel the pulsing then it isn't ABS related

 

yes it's pulsing.

 

Are your sensors bad or did they get dinged while changing rotors?

When I did my spindle lift I had to remove the abs sensors in the stock spindles. I put them in the new spindles and thought everything was fine until what you described was happening to me. MIND you I did have to tap them to remove them so something could have jarred... but cosmetically they looked fine.

Went on amazon and replaced the sensors for new (think they were $30 a pop) and the problem hasn't come back since. Somehow I did something to the sensors when tapping them out of the stock spindle.

-Nigel

 

Then yes, +1 to above.

You have a bad sensor, probably on front wheel since that is where you were working.

Not sure you can test them, I know Ford can with ABS scanner, they spin each wheel and get pulse count.
Sensor is not dead or you would get ABS light, just not showing pulse count at low RPM so ABS thinks wheel is locked up.

 

i had same thing happen to me today and i figured it out just so everyone next time has a simple answer and thing to check!
mine ended up being a manufacturer defect in the rotor abs wheel on the back , one side of the wheel was above the back flat of the rotor inside and part was below , could definitely see it was lopsided. If anyone has abs problem after rotor/brake job its most likely going to be a bad rotor!