BRAKE PEDDLE IS PULSATING AT SLOW SPEEDS AND GOES TO THE FLOOR
2001 Chevrolet Silverado
September, 30, 2011 AT 5:42 PM
When I am stopped at a light and have my foot on the break peddle the ABS kicks in and then peddle goes to the floor and I have no breaks. Only at low speeds does this happen. Breaks work fine at high speeds. I would like to know what some of the causes for this might be. The ABS light does Not come on.
Take this to a pro so he can see if any codes are in it. Autop arts stores can't read abs codes so you need mostly a pro model.
September, 30, 2011 AT 8:51 PM
I just dealt with this identical problem with a friend's Silverado. I fixed it by removing the front wheel speed sensors and cleaning the mounting surface where the sensor meets the hub. Corrosion builds up on the surface and changes the air gap of the hall-effect sensor. Unfortunately, if you live in a "rust belt" state, this may become periodic maintenance. On extreme cases, I've read that the corrosion contaminates the grease in the hub and collects between the teeth of the tone ring. Cleaning is difficult because you don't want to wash the grease out. The alternative is to replace the hubs - this is only necessary in extreme cases; it's also costly in terms of both parts and labor.
If you're not comfortable taking on a repair with moderates skills, I would recommend taking it to a professional. But if you're willing to give it a shot, here are the steps to do it.
1) Safely raise and support the vehicle.
2) Disconnect the front wheel speed sensors from their harness and frame.
3) With a digital volt-meter attached to the terminals of each wheel speed sensor connector, rotate the wheel in a clockwise direction approximately one revolution per second. The minimum reading on the meter should be at least 350 ACmV s. If the reading is less than that, remove the sensor.
4) Plug the sensor bore to prevent debris from falling into the hub.
5) With a wire brush, sandpaper, or another suitable cleaning device, thoroughly clean the speed sensor mounting surface.
6) Examine the sensor head for warpage or distortion due to corrosion build-up. Check the mounting surface of the sensor head for flatness at three or more positions.
7) GM recommends applying two thin coats of rust penetrating lubricant (GM P/N 89022217) to the sensor mounting surface on the bearing hub and allow to dry for 3-5 minutes. Once it has dried, apply a thin layer of bearing grease (GM P/N 01051344) to the hub surface and sensor o-ring, prior to sensor installation.
8) Install the original sensor or replacement sensor in the hub and make certain it is seated flush against the hub.
9) Re-check the sensor voltage while rotating the wheel as previously described. The voltage should read a minimum of 350 ACmV s.