Mustang V6-3.8L VIN 4 (1998)
Brake Master Cylinder: Initial Inspection and Diagnostic Overview
Abnormal Conditions
NOTE: Prior to performing any diagnosis, make sure the brake system warning indicator is functional.
Changes in brake pedal feel or travel are indicators that something could be wrong in the brake system. The diagnostic procedures and techniques use
brake pedal feel, the warning indicator illumination, and brake fluid level as indicators in diagnosing brake system concerns. The following conditions
are considered abnormal and indicate that brake master cylinder is in need of service.
-
Brake pedal goes down fast. This could be caused by an external or internal leak.
-
Brake pedal eases down slowly. This could be caused by an external or internal leak.
-
Brake pedal is low and/or feels spongy. This condition may be caused by no fluid in the brake master cylinder reservoir, reservoir cap vent holes
clogged or air in the hydraulic system.
-
Pedal effort is excessive. This may be caused by a bind or obstruction in pedal/linkage or insufficient booster assist.
-
Rear brakes lock up during light pedal force. This may be caused by wrong tire pressure, grease or fluid on brake linings, damaged brake linings,
improperly adjusted parking brakes, or damaged/contaminated brake pressure control valves.
-
Brake pedal effort is erratic. This condition could be caused by power brake booster malfunction, extreme caliper piston "knock back" or
improperly installed brake lining.
-
Brake warning indicator is ON. This may be caused by low fluid level, ignition wire routing too close to fluid level indicator assembly, or float
assembly damage.
Normal Conditions
Usually, the first and strongest indicator of anything wrong in the brake system is a feeling through the brake pedal.
The following conditions are considered normal and are not indications that the brake master cylinder is in need of service.
-
New brake systems are not designed to produce as hard a pedal effort as in the past. Complaints of light pedal efforts should be compared to pedal
efforts on another vehicle, same model and year.
-
During normal operation of the brake master cylinder, the fluid level in the brake master cylinder reservoir will rise during brake application and
fall during release. The net fluid level, after brake application and release, will remain unchanged.
-
A trace of brake fluid existing on the booster shell below the master cylinder mounting flange. This results from the normal lubricating action of
the master cylinder bore end seal.
-
Fluid level will decrease with pad wear.
Cleaning and Inspection
When in the brake master cylinder area, check the brake tubes and brake master cylinder mounting. The brake tubes and attaching nuts must be tight.
The brake tube fittings must not show any signs of leakage. Tighten the brake tubes at the brake master cylinder to 14-24 Nm (11-17 ft. lbs.).
The following conditions are considered normal and are not indications that the brake master cylinder is in need of service:
-
Low fluid level detected without signs of leakage; this condition is caused by displacement of fluid from the brake master cylinder reservoir into
the rear disc brake calipers, the disc brake calipers, the rear wheel cylinders to compensate for normal brake lining wear. Add fluid as needed.
-
A momentary or slight squirt of brake fluid from the brake master cylinder reservoir upon application of the brake pedal; this condition is caused
by fluid displacement through the brake master cylinder reservoir compensating port as the brake master cylinder pistons move forward in the bore
when the brakes are applied.
-
Slight turbulence in the brake master cylinder reservoir fluid when the brake pedal is released; turbulence occurs as brake fluid returns to the brake
master cylinder after releasing the brakes.
-
A trace of brake fluid found on the outside of the power brake booster below the brake master cylinder mounting flange; this condition results
from the lubricating action of the master cylinder wiping seal.
