Mustang Cobra V8-281 4.6L DOHC VIN V MFI (1997)
Brake Master Cylinder: Initial Inspection and Diagnostic Overview
Brake Fluid Reservoir
Refer to Brakes - System Diagnosis for procedures. See: Testing and Inspection
Normal/Abnormal Conditions
NORMAL CONDITIONS
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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 the brake master cylinder is in need of service:
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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.
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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.
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A slight turbulence in the brake master cylinder reservoir fluid occurring when the brake pedal is released. Turbulence occurs as brake fluid
returns to the brake master cylinder after releasing the brakes.
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A trace of brake fluid exists on booster shell below the brake master cylinder mounting flange. This condition results from the lubricating action of
the master cylinder wiping seal.
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Low fluid level detected without signs of leakage; this condition is caused by displacement of fluid from the brake master cylinder reservoir into
the disc brake calipers to compensate for normal brake wear. Add the specified fluid as needed.
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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.
ABNORMAL CONDITIONS
NOTE: Prior to performing any diagnosis, make sure the brake system warning indicator is functional.
The diagnosis 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 the brake master cylinder is in need of service.
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Brake pedal goes down fast. This could be caused by an external or internal leak.
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Brake pedal eases down slowly. This could be caused by an external or internal leak.
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Brake pedal is low or feels spongy. This condition may be caused by no fluid in the brake master cylinder reservoir, reservoir cap vent holes
clogged, rear brakes out of adjustment or air in the hydraulic system.
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Brake pedal effort is excessive. This may be caused by a bind or obstruction in brake pedal linkage or insufficient power brake booster vacuum.
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Rear brakes lock up during light brake pedal force. This may be caused by wrong tire pressure grease or fluid on linings, damaged linings,
improperly adjusted parking brakes or damaged/contaminated brake pressure control valve.
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Brake pedal effort is erratic. This condition could be caused by power brake booster malfunction extreme caliper piston knock back or improperly
installed disc brake shoe and lining.
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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. A binding parking brake system will also cause the Brake warning indicator to remain "ON".
Prelininary Inspection -- Start Here
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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.
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Tighten the brake tubes at the brake master cylinder to 14-24 Nm (11-17 ft. lbs.).
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Tighten the brake master cylinder mounting nuts to 21-29 Nm (16-21 ft. lbs.).
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The brake tube fittings must not show any signs of leakage.
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Check fluid level in master cylinder. If fluid is extremely low or empty, check for leaks or excessively worn pads. See: Testing and
Inspection/Component Tests and General Diagnostics/Leak Checks See: Disc Brake System/Brake Pad/Testing and Inspection
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Review Normal/Abnormal Conditions under Procedures before continuing diagnosis or replaceing components. See: Normal/Abnormal
Conditions
Fluid Inspection
WARNING: If the swollen brake master cylinder gasket condition is present, all brake system rubber parts must be replaced. All components
containing rubber parts must be overhauled or replaced. All brake tubes must be thoroughly flushed with brake fluid before the vehicle goes
back into service. Contaminated and swollen parts can lead to brake failure.
NOTE: Brake fluid contaminated with a hydrocarbon/mineral based fluid (such as power steering or transmission fluid) can be detected by an obvious
swelling of the master cylinder cap gasket.
If the system is contaminated, replace/rebuild the following components;
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Front and rear calipers.
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Front and rear brake hoses.
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brake pressure control valves.
