Q: How to disconnect and replace the combination valve in a brake system?
A: To replace the brake proportioning valve, disconnect the wire connector from the pressure differential switch. Turn the ignition key to On and check if the warning light lights up. Once the light works, turn off the ignition, disconnect the jumper wire, and reconnect the wire to the switch. Ensure the master cylinder reservoirs are full and attach a bleeder hose to a rear wheel bleeder valve. Turn the ignition on and open the bleeder valve while a helper applies pressure to the brake pedal. The brake warning light should light up. Close the valve before the helper releases the pedal. To replace, disconnect the hydraulic lines, disconnect the electrical connector, remove the bolt holding the valve, and remove the valve. Install in reverse order and bleed the brake system.
Q: What is the purpose of the height sensing proportioning valve in Jeep Wagoneer?
A: The brake proportioning valve, exclusive to Comanche models, adjusts hydraulic pressure to the rear brakes based on truck bed weight. It reduces pressure when the bed is empty to avoid wheel lock-up, and increases it when loaded. Servicing this valve needs special tools and skills, so it's advised to use a dealer service department or qualified repair shop. Suspension modifications altering the distance between the rear axle and frame can give false readings to the valve, risking insufficient braking and accidents.