Expedition 2WD V8-5.4L SOHC VIN L (1997)
Brake Master Cylinder: Component Tests and General Diagnostics
Bypass Conditions Test
1. Check the fluid in the brake master cylinder. Fill the brake master cylinder reservoir if low or empty.
2. Observe the fluid level in the brake master cylinder reservoir. If after several brake applications the fluid level remains the same, measure the
wheel turning torque required to rotate the wheels with brakes applied as follows:
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Apply the brakes slowly to a minimum of 445 N (100 lbs) of force and hold for approximately 15 seconds. With the brakes still applied, exert
torque on the front wheels to 101 Nm (75 ft. lbs.). If the wheel can be rotated, the brake master cylinder is bypassing.
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Repair or replace the brake master cylinder. See: Service and Repair/Master Cylinder, Brakes
Compensator Port Test
SUPPLYING ADDITIONAL FLUID
The purpose of the compensator ports in the brake master cylinder is to supply any additional brake fluid required by the system due to brake pad
wear and to allow brake fluid returning from the brake lines to the brake master cylinder to enter the brake master cylinder reservoir.
FLUID RETURN
The returning brake fluid will cause a slight turbulence in the brake master cylinder reservoir. Turbulence seen in the brake master cylinder
reservoir upon release of the brake pedal is normal and shows that the compensating ports are not plugged.
Non-Pressure Leaks
BRAKE FLUID LOSS
The only part of the brake system that could have a brake fluid loss that does not appear when the system is under pressure is the brake master
cylinder reservoir area. Brake fluid loss could be caused by a missing or poorly-fitted brake master cylinder filler cap, a punctured or otherwise
damaged brake master cylinder reservoir, a missing or damaged brake master cylinder filler cap gasket or by missing, damaged or poorly-fitted
sealing grommets between the brake master cylinder and the brake master cylinder reservoir.
CAUTION: The brake master cylinder reservoir grommets are not separately serviceable and must be replaced as a unit with a new brake master
cylinder reservoir. See: Service and Repair/Master Cylinder, Brakes
