Q: How to replace the brake pressure differential valve on Ford Bronco?
A: If the brake warning light comes on, it indicates a leak or problem detected by the brake proportioning valve, causing the valve piston to shift from its centered position. This shift completes the brake warning light circuit and illuminates the light. To resolve this issue, the valve must be centered. Start by filling the master cylinder reservoir and bleeding the hydraulic system. Block the wheels and release the parking brake. Turn the ignition switch to On or Accessory. If the valve is not centered, the warning light should be on at this point. Place rags under the master cylinder outlet lines and crack open one of the lines using a flare-nut wrench. Have an assistant sit in the driver's seat and slowly push the Brake Pedal down while observing the warning light. The pressure differential within the valve should force it to its centered position, causing the light to go out. Tighten the outlet line fitting and have your assistant release the brake pedal. If this process fails, repeat it on the other outlet line. Check the brake pedal for firmness and operation, and replenish the brake fluid as needed. If the brake proportioning valve is defective or leaking, it must be replaced. Disconnect the brake warning light connector and the front inlet and rear outlet pipe unions from the valve assembly. Plug the ends of the lines to prevent fluid loss and dirt entry. Remove the bolts and nuts securing the valve assembly to the chassis member, taking care to avoid contact between brake fluid and paint. Install the replacement valve, bleed the system, and center the valve as described earlier.