ABS problem?

[Kedi]

Occasionally my brakes grab hard with just a normal application of pedal force. It continues for several applications but does return to normal. Often when doing a hard panic stop it sometimes feels like the brakes have lost friction at some point. I do not feel any pulsing of ABS, increased pressure on the pedal does not seem to have effect. I do brake fairly well. But it feels like I have lost control of the braking. Sometimes, but seldom, one or more wheels lock momentarily, but not all four. Is there something going on with my ABS system?

 

[Uncle Gump]

It's hard to say exactly what you have going on here. I would first pull all the wheels and take a good look at the brakes at all four corners. Ensure all is good with the brake linings... machined surfaces and hardware. I would also ensure you don't have fluid leaks contaminating things (rear axle seals and wheel cylinders). Also that the parking brake isn't hung up. If everything looks good... take a drive with a scan tool hooked up that can read live ABS data. Watch the wheel speed sensor data to ensure they all provide good data. I have seen wheel speed sensors "drop off" at slower speeds even when the truck is still moving.... this causes the ABS system to think a wheel locked up and starts to do what ABS systems do. You typically here the ABS pump kick ON and you can also feel it in the pedal.

 

[Kedi]

I don't have a code reader capable of live display. My Innova 3100J+ shows no codes at all. It does specifically show ABS codes. No codes is pretty nice for +200,000 kilometers. I am going to take it in for rear shoe replacement soon. Or maybe do it myself. On holidays soon. The brake slipping feeling under hard braking may be due to worn rear shoes? But the hard grabbing even on light application is weird. And then it goes away quickly. Maybe I should take it in for shoe replacement and ask them to check the ABS too. Seems like I found a good guy for repairs I don't want to do myself. I always use the emergency brake when parking. So it is unlikely that it is frozen. That did happen on my old Bronco. One reason I got it so cheap. The seller didn't know why it was messed up.

 

[Dirtman]

Brakes can grab hard when rust forms on the discs or drums, once its removed after a few stops braking usually returns to normal. Id pop the rear drums off and have a gander...