Diagnosis and Inspection
DIAGNOSIS AND INSPECTION
BRAKE SYSTEM TESTING
Test brakes on a dry, clean, reasonably smooth and level roadway. A true test of brake performance cannot be made if roadway is wet, greasy, or covered with loose dirt so that all tires do not grip the road equally. Testing is adversely affected when the roadway is crowned, throwing the weight of the vehicle toward the wheels on one side, or when the roadway is so rough, making the wheels bounce. Test the brakes at different vehicle speeds with both light and heavy pedal pressure. Because of a high deceleration capability, a firmer pedal may be felt at higher deceleration rates.
External Conditions That Affect Brake Performance
1. Tires. Tires having unequal contact and grip on road will cause unequal braking. Tires must be equally inflated, identical in size, and the tread pattern of right and left tires must be approximately equal.
2. Vehicle Loading. A heavily loaded vehicle requires more braking effort. When a vehicle has unequal loading, the most heavily loaded wheels require more braking power than others.
3. Wheel Alignment. Misalignment of the wheels, particularly in regard to excessive camber and caster, will cause the brakes to pull to one side.
4. Trailer Towing. Towing a trailer requires longer braking distances and tends to overheat the brakes sooner.
Brake Fluid Leaks
With the engine running at idle and the shift lever in neutral, depress the brake pedal and hold a constant foot pressure on the pedal. If the pedal gradually falls away with the constant pressure, the hydraulic system may be leaking. Perform a visual inspection to confirm any suspected leak.
Check the master cylinder fluid level. While a slight drop in reservoir level does result from normal lining wear, an abnormally low level in either reservoir may indicate a leak in the system. The hydraulic system may be leaking either internally or externally. Also, the system may appear to pass this test but still have slight leakage.
If the fluid level is normal and no external leaks are found at the brake pipe or hose connections or at the caliper or wheel cylinder boots, check the service brake pedal travel, brake adjustment and the parking brake adjustment.
Master Cylinder Check
These checks will not determine all master cylinder malfunctions. Use the Brake System Diagnosis chart to help isolate the problem if it is not found by using these tests.
1. Check for a cracked master cylinder casting or brake fluid around the master cylinder. Leaks are indicated even if there is only a drop of fluid. A damp condition is not abnormal.
2. Check for a binding pedal linkage. If satisfactory, disassemble the master cylinder and check for swollen or elongated primary piston seal(s). If swollen seals are found, substandard or contaminated brake fluid should be suspected. If contaminated, all components should be disassembled and cleaned; all rubber components should be replaced and all pipes flushed.
CAUTION: Brake fluid may be irritating to skin or eyes, or may cause nausea, vomiting or diarrhea if swallowed. In case of contact or swallowing take the following actions:
^ Eye contact - rinse thoroughly with water.
^ Skin contact - wash with soap and water.
^ If swallowed - Contact a physician immediately. Give two glasses of water and induce vomiting by sticking finger down throat.
NOTICE: Avoid spilling brake fluid on any of the vehicle's painted surfaces, wiring, cables or electrical connectors. Brake fluid will damage paint and electrical connections. If any fluid is spilled on the vehicle, flush the area with water to lessen the damage.
Important
^ Use only Delco Supreme II Brake Fluid GM P/N 1052535, or equivalent DOT-3 brake fluid.
^ Do not use power steering or transmission fluid in the brake system.
^ Do not re-use brake fluid accumulated during brake system bleeding.
^ Always store brake fluid in a closed container. Re-seal brake fluid containers immediately after use. Do not use brake fluid left in an open or improperly sealed container because it absorbs moisture or can become contaminated.
Improper brake fluid, mineral oil i.e., power steering fluid and transmission fluid or water in the fluid may cause the fluid to boil, or the rubber components in the brake hydraulic system to deteriorate.
If the master cylinder cap diaphragm is swollen, then rubber parts have deteriorated. This deterioration may also be evidenced by swollen wheel cylinder boots and caliper boots.
If deterioration of rubber parts is evident, disassemble all serviceable hydraulic components and wash with alcohol. Dry these parts with non-lubricated compressed air before assembly to keep alcohol out of the system. Replace ALL rubber parts in the system, including hoses and non-serviceable hydraulic components.
Refill the brake system with new brake fluid, flush and bleed it.
WARNING LIGHT OPERATIONS
Standard Brake System
The standard brake system uses a single red "BRAKE" warning light located in the instrument panel cluster. When the ignition switch is in the "Start" position, the "BRAKE" warning light should glow and go off when the ignition switch returns to the "Run" position.
The following conditions will activate the "BRAKE" light:
1. Parking brake applied. The light should be on whenever the parking brake is applied and the ignition switch is on.
2. Low fluid level. A low fluid level in the master cylinder will turn the "BRAKE" light on.
ANTILOCK BRAKE SYSTEM
The antilock brake system uses two indicator lamps, a red "BRAKE" warning lamp and an amber "ANTILOCK" lamp, both located in the instrument panel cluster. Under normal conditions, these lamps should activate as follows:
1. When ignition is turned to the "RUN" position, prior to starting the engine, the amber "ANTILOCK" lamp should turn "ON".
2. As the engine is cranked, the red "BRAKE" lamp and the amber "ANTILOCK" lamp should come "ON".
3. When the engine is started, both lamps should be "OFF".
BRAKE FLUID
CAUTION: Brake fluid may be irritating to skin or eyes, or may cause nausea, vomiting or diarrhea if swallowed. In case of contact or swallowing take the following actions:
^ Eye contact - rinse eyes thoroughly with water.
^ Skin contact - wash skin with soap and water.
^ If swallowed - contact a physician immediately. Give two glasses of water and induce vomiting by sticking finger down throat
NOTICE: Brake fluid will damage painted surfaces. Brake fluid can also damage electrical connections. Use shop cloths and fender covers to prevent brake fluid from contacting such surfaces. Always reseal and wipe brake fluid containers clean to prevent spillage.
Use Delco Supreme II Brake Fluid (GM P/N 1052535) or an equivalent DOT-3 motor vehicle brake fluid. DOT-5 silicone fluid is not recommended for use in the vehicle's base brake system. DOT-5 brake fluid should never be used in the antilock brake system.
Brake fluid should always be stored in a closed container. Reseal brake fluid containers immediately after use. Brake fluid left in an open or improperly sealed container will absorb moisture. This can lower the fluid's boiling point and may result in system contamination, corrosion or deterioration of rubber components.
Substandard or Contaminated Brake Fluid
NOTICE: Use only DOT 3 brake fluid from a clean, sealed container. Do not use any fluid from a container which is wet with water. Do not use DOT 5 silicone brake fluid. Improper brake fluid, mineral oil or water in the fluid may cause the brake fluid to boil or the rubber components to deteriorate. Keep all fluid containers capped to prevent contamination.
Important: Improper brake fluid, mineral oil or water in the fluid may cause the brake fluid to boil or the rubber components in the hydraulic system to deteriorate.
Inspect
Upon inspection, if primary piston cups are swollen, then rubber parts have deteriorated. This deterioration may also be evidenced by swollen wheel cylinder piston cups on the drum brake wheel cylinders or the master cylinder cover diaphragm.
If deterioration of rubber is evident, disassemble ~l hydraulic parts and wash with alcohol. Dry these parts with unlubricated compressed air before assembly to keep alcohol out of the system. Replace all rubber parts in the system, including hoses. Also, when working on the brake mechanisms, check for fluid on the brake linings. If any fluid is found, replace the linings.
If master cylinder piston seals are satisfactory, check for leakage or excessive heat conditions. If condition is not found, drain fluid, flush with brake fluid, refill and bleed the system.