NBS braking issue, brakes lock up while stopping at slow speeds

Discussion in 'Engine & Drivetrain Tech' started by a-fuso, Dec 6, 2016.

  1. a-fuso

    a-fuso GMC Owner

    Messages:
    1,856
    Okay I will try to explain the issues I have been having for about 6 months now. I have a '02 1500 with original size calipers and rotors in front, and nbs suv rear calipers and rotors in the rear, lml hydroboost swap, new hb unit and new gm power steering pump and am still having the issue. Rear has stainless braided brake lines, however, I have not installed my front lines yet.

    So for a while now, when turning and maneuvering in parking lots, the brake pedal will get hard like when the ABS kicks in, but it does it at very slow speeds. The truck stops its current rate of slowing and continues like the brakes are not being pressed since the pedal is now firm. You have to over-power the pedal and press past it, otherwise most of the time you're in danger of hitting something when not expecting the pedal to lock up. Add a trailer behind the truck and it gets worse. Slowing from 55-15 mph is like normal when applying the brakes, then at the last minute, say before a stop sign limit line, the pedal will get hard and lock up, forcing you through an intersection unless both feet are used to power past the pedal again at the last feew feet.

    The brakes do not do this every time, but it does more often than not. I fixed my abs module circuit board about a year ago when my dash lights were on constantly, no more lights now. I suspected this may be caused by the abs system so I have tried towing with the abs fuse removed, and still had the same issue. So I'm at a loss now what to check next. Anyone ever experience this or heard of something similar?
     
  2. Bassmaster

    Bassmaster Media Mod

    Messages:
    10,287
    Happened on my old sierra. Common problem was the pulsing brake pedal at low speeds. I swapped the front hubs & wheel speed sensors with it and fixed it
     
  3. Graystone

    Graystone Well-Known Member

    Messages:
    1,304
    Check for play in the hub. If there is play replace hub. If not it's abs sensors.
     
  4. Cleanoh4

    Cleanoh4 Well-Known Member

    Messages:
    4,325
    ABS Low Speed Activation

    Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #03-05-25-007 - (09/29/2003)


    Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)
    2002-2004 Cadillac Escalade, Escalade EXT

    2003-2004 Cadillac Escalade ESV

    1999-2004 Chevrolet Silverado

    2001-2004 Chevrolet Suburban, Tahoe

    2002-2004 Chevrolet Avalanche

    2003-2004 Chevrolet Express

    1999-2004 GMC Sierra

    2001-2004 GMC Yukon, Yukon XL

    2003-2004 GMC Savana

    2003-2004 HUMMER H2

    Condition
    Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

    Cause
    The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

    Correction
    Measure AC voltage and clean the wheel speed sensor mounting surfaces.

    Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual (SI Document ID #899664).
    Disconnect both the front wheel speed sensor (WSS) connectors at the frame and harness.
    Place a Digital Volt Meter (DVM) across the terminals of each WSS connector.
    Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual. Plug the WSS bore in order to prevent debris from falling into the hub during service.
    Clean the WSS mounting surface on the hub to remove any rust or corrosion using a wire brush, or equivalent.

    Important
    Make sure that the sensor sits flat on the hub. Check the sensor flange against a straight edge to ensure flatness. If the sensor flange is distorted, replace the sensor.


    Apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344.
    Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
    Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's.
     
  5. a-fuso

    a-fuso GMC Owner

    Messages:
    1,856
    Thanks for the info Mike, I'll have to take the front end apart for balljoints very soon, so I'll check into cleaning/replacing those sensors. I check my hubs every few months and they don't have any play in them yet.
     

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