F 150 4WD Pickup V8-281 4.6L VIN W EFI (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 (with the key off) required to rotate the wheels with brakes applied as follows:
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Apply the brakes slowly to a minimum of 445 Kgm (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 lb/ft). If the wheel can be rotated, the brake master cylinder is bypassing. Repair or replace the
brake master cylinder. Refer to Master Cylinder, Brakes Service and Repair in this section.
Compensator Port Test
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.
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
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.
The brake master cylinder reservoir grommets are not separately serviceable and must be replaced as a unit with a new brake master
Proportioning Valve Check
If there is a brake system concern such as premature rear brake lockup that cannot be attributed to the Rear Anti-lock Brake System (RABS), the cause
may be a malfunctioning brake master cylinder fluid control valve.
Check the brake master cylinder fluid control valve by substituting the suspected bad valve with a known good one. If the condition persists, recheck the
RABS; refer to Antilock Brake System. See: Testing and Inspection
