Master Cylinder Diagnosis - GMC chervolet camaro 1999 Service Manual

5-22 Hydraulic Brakes
Master Cylinder Diagnosis
Notice: Avoid spilling brake fluid on any of the painted
vehicle's surfaces, wiring, cables or electrical
connectors. Brake fluid will damage paint and electrical
connections. If any fluid is spilled on the vehicle,
immediately flush the area with water to minimize
potential for damage.
Visual Inspection
• Check for a cracked casting or brake fluid leaks
around the master cylinder. A leak will have at
least one drop of fluid. A damp condition is normal.
• Check .the pedal linkage for binding and for
incorrect pushrod.length. Disassemble the master
cylinder if you do not find improper brake pedal
travel or brake pedal binding. ·
• Check the master cylinder for swollen or elongated
primary piston seals. If you find swollen seals,
refer to Brake Fluid and Brake Fluid Handling.
Low Pressure Check
This procedure inspects the following conditions:
• Internal seal damage
• porosity
• Component bore integrity
1. With the ignition switch in the OFF position, pump
the brake pedal in order to relieve the vacuum.
• Pump the brake pedal five times for
vacuum-assisted brakes.
• Pump the brake pedal twenty-five times for
hydraulic-assisted brakes.
2. Apply the brake pedal slowly (approximately 3 mm
[{]1/8 in[}] per second). This generates pressure
in the master cylinder.
Brakes
3. Gradually increase pedal force. Observe for
gradually increasing brake pedal travel
(Falling Away).
4. If the brake pedal travel tends to gradually
increase; preform the High. Press1.1re Check.
5. If the High Pressure Check does not locate a
··leak, then the.master cylinder has an internal leak.
High Pressure Check
This procedure tests for the following conditions:
• Leaks at the following locations:
- Connections
- Hoses
- Casting
• Large Internal Leaks
1. With the engine running, apply the brake pedal
slowly (approximately 3 mm [{]1/8 in[}] per
second). This generates pressure in the master
cylinder.
2. Gradually increase pedal force. Observe for
gradually increasing brake pedal travel
(Falling Away).
3. Check for evidence of external fluid leaks.
Examine the following items:
• The ground
• The pipe connections
• The tires
4. If you observe fluid around any component, that
component has failed and needs to be replaced.
5. If you find a leak at a connection, tighten
the connection to specification, Refer to Fastener
Tightening Specifications.
6. Perform the High Prsssure Check again.
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