| Diagnosis and Testing Inspection and Verification NOTE:Before carrying out any diagnosis, make sure that the brake system warning indicator operates correctly. - Verify the customer concern, carrying a road test with the customer if necessary.
REFER to: Road/Roller Testing (100-00 General Information, Description and Operation).
- Visually inspect for obvious signs of mechanical damage.
Visual Inspection Chart | Mechanical | - Tire pressure(s)
- Wheels and tires
- Brake line(s)
| - If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
- If the cause is not visually evident, verify the symptom and refer to the Symptom Chart.
Symptom Chart | Symptom | Possible Sources | Action | | The brakes pull or drift | * Brake pads or brake shoes. * Front brake disc(s). * Brake caliper(s). * Wheel alignment. | * | | * Wheel bearing(s) | * CHECK or INSTALL new wheel bearings as necessary. REFER to: Front Suspension (204-01 Front Suspension, Diagnosis and Testing), Rear Suspension (204-02 Rear Suspension, Diagnosis and Testing). | | The red brake warning indicator is always on | * Brake fluid level. | * FILL the brake system to specification. INSPECT the brake lines for leaks. | | * Brake master cylinder primary piston cup. | * INSTALL a new brake master cylinder.
REFER to: Brake Master Cylinder (206-06 Hydraulic Brake Actuation, Removal and Installation).
| | * Parking brake control. | * RELEASE and ADJUST the parking brake cable. REFER to: (206-05A Parking Brake and Actuation) Parking Brake Cable Adjustment - Vehicles With: Rear Drum Brakes (General Procedures), Parking Brake Cable Adjustment - Vehicles With: Rear Disc Brakes (General Procedures). | | * Circuit. * Anti-lock braking system (ABS). | * | | Vibration when brakes are applied | * Grease or fluid on brake pads or brake shoes; glazed linings. * Brake drum contact surface. | * | | * Brake caliper retaining bolts. | * TIGHTEN the brake caliper bolts. | | * Insufficient grease on sliding parts. | * APPLY grease as necessary. | | * Foreign material or scratches on front brake disc contact surfaces. | * INSTALL a new brake disc. REFER to: Brake Disc - RWD (206-03 Front Disc Brake, Removal and Installation), Brake Disc - FWD (206-03 Front Disc Brake, Removal and Installation), Brake Disc - FWD (206-04 Rear Disc Brake, Removal and Installation), Brake Disc - RWD (206-04 Rear Disc Brake, Removal and Installation). | | * Loose wheel hub nuts. | * TIGHTEN or INSTALL new wheel hub nuts. | | * Wheel bearings. | * CHECK or INSTALL new wheel bearings as necessary. REFER to: Front Wheel Bearing (204-01 Front Suspension, Removal and Installation), Wheel Bearings, Wheel Hub Seal and Wheel Bearing Cups (205-02B Wheel Hubs and Bearings - Full Floating Axle, Removal and Installation). | | * Wheel and tire imbalance. | * CHECK and BALANCE the wheels and tires as necessary. | | The brake pedal goes down fast | * Leak in brake system. | * | | * Air in the brake system. | * BLEED the brakes. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). | | * Brake master cylinder. | * INSTALL a new brake master cylinder.
REFER to: Brake Master Cylinder (206-06 Hydraulic Brake Actuation, Removal and Installation).
| | * Brake pads and brake shoes. | * INSPECT the brake pads and brake shoes. REPAIR or INSTALL new brake pads or brake shoes as necessary. REFER to: Brake Pads (206-03 Front Disc Brake, Removal and Installation), Brake Pads (206-04 Rear Disc Brake, Removal and Installation), Brake Shoes (206-02 Drum Brake, Removal and Installation). | | The brake pedal eases down slowly | * Air in the brake system. | * BLEED the brakes. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). | | * Brake master cylinder. | * | | The brake pedal is low or feels spongy. | * Brake pads or brake shoes. | * INSPECT the brake pads and brake shoes. INSTALL new brake pads or brake shoes as necessary. REFER to: Brake Pads (206-03 Front Disc Brake, Removal and Installation), Brake Pads (206-04 Rear Disc Brake, Removal and Installation), Brake Shoes (206-02 Drum Brake, Removal and Installation). | | * Brake system. | * | | Brake lockup during light brake pedal force. | * Brake pads or brake shoes. * Brake calipers. * Brake load sensor proportioning valve. | * | | Excessive/erratic brake pedal travel | * Brake pads or brake shoes. | * INSPECT the brake pads and brake shoes. REPAIR or INSTALL new brake pads or brake shoes as necessary. REFER to: Brake Pads (206-03 Front Disc Brake, Removal and Installation), Brake Pads (206-04 Rear Disc Brake, Removal and Installation), Brake Shoes (206-02 Drum Brake, Removal and Installation). | | * Air in the brake system. | * Bleed the brake. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). | | Brakes drag | * Brake booster. * Seized brake caliper/wheel cylinder. * Parking brake control applied/inoperative/over adjusted. * Seized parking brake cables. * Seized brake caliper slide pins. | * | | Excessive brake pedal effort | * Brake booster. | * CHECK the brake booster. Carry out the component test. REPAIR or INSTALL a new brake booster as necessary.
REFER to: Brake Booster (206-07 Power Brake Actuation, Removal and Installation).
| | * Brake pads or brake shoes. | * INSPECT the brake pads and brake shoes. REFER to: Specifications (206-03 Front Disc Brake, Specifications), Specifications (206-04 Rear Disc Brake, Specifications), Specifications (206-02 Drum Brake, Specifications). | | * Brake booster check valve. | * | | Slow or incomplete brake pedal return | * Brake booster. * Brake master cylinder. | * | Pinpoint Tests | PINPOINT TEST A : THE BRAKES PULL OR DRIFT. | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | A1: INSPECT THE BRAKE PADS OR BRAKE SHOES | | | 1 Check the brake pads or brake shoes for grease or fluid on the linings and excessive wear. | | | Are the brake pad or brake shoe linings contaminated, or worn excessively? Yes INSTALL new brake pads or brake shoes. REFER to: Brake Pads (206-03 Front Disc Brake, Removal and Installation), Brake Pads (206-04 Rear Disc Brake, Removal and Installation), Brake Shoes (206-02 Drum Brake, Removal and Installation). No | | A2: INSPECT THE BRAKE CALIPERS | | | 1 Check the brake caliper components for binding, leaking or sticking. | | | Is there evidence of leaks, or do the pistons and pins bind or stick? Yes INSTALL new pistons or pins as necessary. REFER to: Brake Caliper (206-03 Front Disc Brake, Removal and Installation), Brake Caliper (206-04 Rear Disc Brake, Removal and Installation). TEST the system for normal operation. No | | A3: INSPECT THE BRAKE DISCS | | | 1 Check the brake discs for damage. | | | Are the brake discs damaged? Yes INSTALL new brake discs. REFER to: Brake Disc - RWD (206-03 Front Disc Brake, Removal and Installation), Brake Disc - FWD (206-03 Front Disc Brake, Removal and Installation), Brake Disc - FWD (206-04 Rear Disc Brake, Removal and Installation), Brake Disc - RWD (206-04 Rear Disc Brake, Removal and Installation). No | | A4: CHECK THE VEHICLE WHEEL ALIGNMENT | | | 1 Check the vehicle wheel alignment. | | | Is the wheel alignment within specification? Yes Vehicle is OK. VERIFY the customer concern. No ADJUST the wheel alignment as necessary. REFER to: (204-00 Suspension System - General Information) Specifications (Specifications), Front Toe Adjustment (General Procedures). TEST the system for normal operation. | | PINPOINT TEST B : THE RED BRAKE WARNING INDICATOR IS ALWAYS ON | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | B1: CHECK THE RED BRAKE WARNING INDICATOR | | | 1 Ignition switch in position II. | | | Is the red brake warning indicator on? Yes Vehicles with ABS, REFER to WDS. No Vehicle is OK. VERIFY the customer concern. | | B2: CHECK THE PARKING BRAKE | | | 1 Check the parking brake is fully released. | | | Does the red brake warning indicator go out? Yes Vehicle is OK. TEST the system for normal operation. No | | B3: CHECK THE PARKING BRAKE SWITCH FOR SHORT TO GROUND | | | 1 Disconnect Parking Brake Warning Indicator Switch. | | | Does the red brake warning indicator go out? Yes INSTALL a new parking brake warning indicator switch. TEST the system for normal operation. No | | B4: CHECK THE BRAKE FLUID LEVEL | | | 1 Check the brake fluid level in the brake fluid reservoir. | | | Is the brake fluid level within specification? Yes No FILL the brake fluid reservoir to the MAX mark. | | B5: CHECK THE BRAKE FLUID LEVEL SWITCH FOR SHORT TO GROUND | | | 1 Disconnect Brake Fluid Level Switch. | | | Does the red brake warning indicator go out? Yes INSTALL a new brake fluid level switch. TEST the system for normal operation. No | | B6: CHECK CIRCUIT 31S-GC6/31S-GC7 (BK/BU) FOR SHORT TO GROUND | | | 1 Ignition switch in position 0. | | | 2 Disconnect Instrument Cluster (C220b). | | | 3 Measure the resistance between the instrument cluster C220b pin 3, circuit 31S-GC6/31S-GC7 (BK/BU) and ground. | | | Is the resistance greater than 10,000 ohms? Yes INSTALL a new instrument cluster.
REFER to: Instrument Cluster (413-01 Instrument Cluster, Removal and Installation).
TEST the system for normal operation. No REPAIR circuit 31S-GC6/31S-GC7 (BK/BU). TEST the system for normal operation. | | PINPOINT TEST C : VIBRATION WHEN BRAKES ARE APPLIED | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | C1: ROAD TEST THE VEHICLE | | | 1 Road test the vehicle between 40-80 km/h (25-50 mph) without depressing the brakes. | | | Is a vibration present? Yes TEST for noise, vibration and harshness.
REFER to: Noise, Vibration and Harshness (NVH) (100-04 Noise, Vibration and Harshness, Diagnosis and Testing).
REPEAT the road test if necessary. No | | C2: CHECK FOR REAR BRAKE VIBRATION | | | 1 Road test the vehicle between 40-80 km/h (25-50 mph) with medium application on the parking brake control only. | | | Is a vibration present? Yes CHECK the brake drums and brake shoes for excessive wear. REFER to: Specifications (206-03 Front Disc Brake, Specifications), Specifications (206-04 Rear Disc Brake, Specifications), Specifications (206-02 Drum Brake, Specifications). INSTALL new brake drums or brake shoes as necessary. REFER to: Brake Pads (206-03 Front Disc Brake, Removal and Installation), Brake Pads (206-04 Rear Disc Brake, Removal and Installation), Brake Shoes (206-02 Drum Brake, Removal and Installation). TEST the system for normal operation. No | | C3: CHECK FOR FRONT BRAKE VIBRATION | | | 1 Road test the vehicle between 40-80 km/h (25-50 mph) with light and medium application on the brake pedal. | | | Is a vibration present? Yes CHECK the brake discs and brake pads for excessive wear. REFER to: Specifications (206-03 Front Disc Brake, Specifications), Specifications (206-04 Rear Disc Brake, Specifications), Specifications (206-02 Drum Brake, Specifications). INSTALL new brake discs or brake pads as necessary. REFER to: Brake Pads (206-03 Front Disc Brake, Removal and Installation), Brake Pads (206-04 Rear Disc Brake, Removal and Installation), Brake Shoes (206-02 Drum Brake, Removal and Installation). TEST the system for normal operation. No Vehicle is OK. VERIFY the customer concern. | | PINPOINT TEST D : THE PEDAL GOES DOWN FAST | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | D1: CHECK THE BRAKE PEDAL EFFORT | | | 1 Road test the vehicle and depress the brake pedal. | | | Is the brake pedal effort OK? Yes Vehicle is OK. VERIFY the customer concern. No | | D2: CHECK THE BRAKE FLUID LEVEL | | | 1 Check the brake fluid level in the brake fluid reservoir. | | | Is the brake fluid level between the MAX and MIN mark? Yes No INSPECT the brake fluid reservoir sealing points. For additional information, refer to the procedure Brake Master Cylinder component test in this procedure. ADD brake fluid and BLEED the brake system. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). INSPECT the brake system for further leaks. TEST the system for normal operation | | D3: CHECK THE BRAKE PEDAL HEIGHT - PRESSURIZE THE SYSTEM | | | 1 Pump the brake pedal rapidly five times and hold in the depressed position. | | | Does the brake pedal height build up and then hold? Yes BLEED the brake system. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). TEST the system for normal operation. ROAD TEST as necessary. No | | D4: CHECK THE BRAKE SYSTEM FOR LEAKS | | | 1 Inspect for external brake system leaks. For additional information, refer to the procedure Brake Master Cylinder component test in this section. | | | Are leaks found? Yes REPAIR as necessary. ADD brake fluid and BLEED the brake system. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). TEST the system for normal operation. No | | D5: CHECK BRAKE MASTER THE CYLINDER BYPASS CONDITION | | | 1 Test for brake master cylinder bypass condition. For additional information, refer to the procedure Brake Master Cylinder component test in this section. | | | Are any concerns found? Yes INSTALL a new brake master cylinder.
REFER to: Brake Master Cylinder (206-06 Hydraulic Brake Actuation, Removal and Installation).
No System is OK. | | PINPOINT TEST E : THE PEDAL EASES DOWN SLOWLY | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | E1: CHECK THE BRAKE PEDAL OPERATION | | | 1 Check if the condition occurs during actual stopping application by depressing the brake pedal while the vehicle is moving. | | | Does the condition occur when the vehicle is moving? Yes No | | E2: CHECK THE BRAKE SYSTEM FOR LEAKS | | | 1 Check for external brake system leaks. For additional information, refer to the procedure Brake Master Cylinder component test in this section. | | | Are leaks found? Yes REPAIR as necessary. ADD brake fluid and BLEED the brake system. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). TEST the system for normal operation. No | | E3: CHECK THE BRAKE MASTER CYLINDER BYPASS CONDITION | | | 1 Test the brake master cylinder bypass condition. For additional information, refer to the procedure Brake Master Cylinder component test in this section. | | | Are any concerns found? Yes INSTALL a new brake master cylinder. REFER to: Brake Master Cylinder (206-06 Hydraulic Brake Actuation, Removal and Installation). TEST the system for normal operation. No System is OK. | | PINPOINT TEST F : THE PEDAL IS LOW OR FEELS SPONGY | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | F1: CHECK FOR SPONGY BRAKE PEDAL FEEL | | | 1 Road test the vehicle and depress the brake pedal. | | | Is the brake pedal effort normal? Yes Vehicle is OK. VERIFY the customer concern. No | | F2: CHECK BRAKE PEDAL RESERVE | NOTE:The increased resistance may feel like the brake pedal has bottomed out. | | | 1 Ignition switch in position III. | | | 2 Engine at idle. | | | 3 Pump the brake pedal lightly three or four times. | | | 4 Wait 15 seconds for the vacuum to replenish. | | | 5 Depress the brake pedal until it stops moving downwards or an increased resistance to the brake pedal travel occurs. | | | 6 Hold the brake pedal in the depressed position while increasing the engine speed to 2000 rpm. | | | 7 Release the accelerator pedal. | | | Does the brake pedal move downwards as the engine speed returns to idle? Yes No CHECK the vacuum to the brake booster. For additional information, refer to the procedure Brake Booster component test in this procedure. | | F3: CHECK THE BRAKE FLUID LEVEL | | | 1 Check the brake fluid reservoir fluid level. | | | Is the brake fluid level between the MAX and MIN mark? Yes BLEED the brake system. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). TEST the system for normal operation. No CHECK the brake fluid reservoir sealing points. For additional information, refer to the procedure Brake Master Cylinder component test in this procedure. ADD fluid and BLEED the brake system. REFER to: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). TEST the system for normal operation. ROAD TEST as necessary. REFER to: Road/Roller Testing (100-00 General Information, Description and Operation). | | PINPOINT TEST G : BRAKE LOCKUP DURING LIGHT BRAKE PEDAL FORCE | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | G1: TEST BRAKE LOCKUP | | | 1 Road test the vehicle and depress the brake pedal lightly. | | | Do the rear brakes lockup? Yes No Vehicle is OK. VERIFY the customer concern. | | G2: INSPECT THE BRAKE PADS OR BRAKE SHOES | | | 1 Inspect the brake pads and brake shoes for grease or fluid on the linings and wear concerns, correct installation, damage, correct size and type. | | | Are any concerns found? Yes INSTALL new brake shoes. REFER to: Brake Pads (206-03 Front Disc Brake, Removal and Installation), Brake Pads (206-04 Rear Disc Brake, Removal and Installation), Brake Shoes (206-02 Drum Brake, Removal and Installation). TEST the system for normal operation. ROAD TEST as necessary. No | | G3: CHECK THE BRAKE LOAD SENSOR PROPORTIONING VALVE | | | 1 Check the brake load sensor proportioning valve for correct installation and adjustment.
REFER to: Brake Load Sensor Proportioning Valve Adjustment (206-00 Brake System - General Information, General Procedures).
| | | Is the brake load sensor proportioning valve correctly adjusted? Yes INSTALL a new brake load sensor proportioning valve. TEST the system for normal operation. No Adjust the brake load sensor proportioning valve.
REFER to: Brake Load Sensor Proportioning Valve Adjustment (206-00 Brake System - General Information, General Procedures).
| | PINPOINT TEST H : BRAKE DRAG | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | H1: ROAD TEST THE VEHICLE | | | 1 Road test the vehicle and apply the brakes. | | | Are the brakes functioning correctly? Yes Vehicle is OK. VERIFY the customer condition. No INSPECT individual wheel cylinders or brake calipers and INSTALL new wheel cylinders or brake calipers as necessary. REFER to: Brake Caliper (206-03 Front Disc Brake, Removal and Installation), Brake Caliper (206-04 Rear Disc Brake, Removal and Installation), Wheel Cylinder (206-02 Drum Brake, Removal and Installation). GO to H2. | | H2: CHECK THE BRAKE BOOSTER | | | 1 Check the brake booster actuating rod alignment and travel. | | | Is the actuating rod OK? Yes Vehicle is OK. VERIFY the customer condition. No INSTALL a new brake booster.
REFER to: Brake Booster (206-07 Power Brake Actuation, Removal and Installation).
TEST the system for normal operation. | | PINPOINT TEST I : EXCESSIVE BRAKE PEDAL EFFORT | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | I1: CHECK THE VACUUM | | | 1 Disconnect the vacuum hose from the brake booster. | | | 2 Connect the vacuum/pressure tester to the vacuum hose. | | | 3 Ignition switch in position III. | | | 4 Run the engine at normal operating temperature. | | | 5 Record the vacuum reading. | | | Is the vacuum reading 40.5kPa (12in-Hg)? Yes No LOCATE and REPAIR the source of low vacuum. TEST the system for normal operation. | | I2: INSPECT THE VACUUM SYSTEM | | | 1 Ignition switch in position 0. | | | 2 Reconnect the vacuum hose. | | | 3 Inspect the brake booster, rubber grommet, and all vacuum hoses for cracks, holes, bad connections, or missing clamps. | | | 4 Pump the brake pedal five times to exhaust the vacuum and hold in the depressed position. | | | Does the brake pedal move down when the engine is started? Yes Vacuum system is OK. No | | I3: CHECK THE BRAKE BOOSTER CHECK VALVE | | | 1 Check the brake booster check valve. For additional information, refer to the procedure Brake Booster component test in this section. | | | Is the brake booster check valve OK? Yes CHECK the brake booster. For additional information, refer to the procedure Brake Booster component Test in this section. INSTALL a new brake booster as necessary.
REFER to: Brake Booster (206-07 Power Brake Actuation, Removal and Installation).
TEST the system for normal operation. No INSTALL a new brake booster check valve. TEST the system for normal operation. | | PINPOINT TEST J : SLOW OR INCOMPLETE BRAKE PEDAL RETURN | | TEST CONDITIONS | DETAILS/RESULTS/ACTIONS | | J1: CHECK THE BRAKE PEDAL RETURN | | | 1 Ignition switch in position III. | | | 2 Run the engine at fast idle while making several brake applications. | | | 3 Pull the brake pedal rearward with approximately 44.5 N (10lb) of force. | | | 4 Release the brake pedal and measure the pedal travel. From the floor pan to the pedal rubber. | | | 5 Make a hard brake application. | | | 6 Release the brake pedal and measure the brake pedal travel. The brake pedal should return to its original position. | | | Does the brake pedal return to its original position? Yes Vehicle is OK. VERIFY the customer concern. No | | J2: CHECK FOR BRAKE PEDAL BINDING | | | 1 Check the brake pedal to make sure it is operating freely. | | | Is the brake pedal operating freely? Yes INSTALL a new brake booster.
REFER to: Brake Booster (206-07 Power Brake Actuation, Removal and Installation).
TEST the system for normal operation. No REPAIR or INSTALL new brake pedal bushings. REFER to: Brake Pedal and Bracket (206-06 Hydraulic Brake Actuation, Removal and Installation). TEST the system for normal operation. | Component Tests Brake Booster - Inspect all hoses and connections. All unused vacuum connectors should be capped. Hoses and their connections should be correctly secured and in good condition with no holes and no collapsed areas. Inspect the brake booster check valve for damage.
- Check the hydraulic brake system for leaks or low fluid.
- With the transmission in PARK (automatic transmission), stop the engine and operate the parking brake. Operate the brake pedal several times to exhaust all vacuum in the system.
- With the engine turned OFF and all vacuum in the system exhausted, operate the brake pedal and hold it down. Start the engine. If the vacuum system is operating, the brake pedal will tend to move downward under constant foot pressure. If no motion is felt, the vacuum booster system is not functioning.
- Remove the vacuum hose from the brake booster. Manifold vacuum should be available at the brake booster end of the hose with the engine at idle speed and the transmission in PARK or NEUTRAL. Make sure that all unused vacuum outlets are correctly capped, hose connectors are correctly secured and vacuum hoses are in good condition. When it is established that manifold vacuum is available to the brake booster, connect the vacuum hose to the brake booster and repeat Step 3. If no downward movement of the brake pedal is felt, the vacuum booster system is not functioning.
- Run the engine for a minimum of 10 seconds at fast idle. Stop the engine and let the vehicle stand for 10 minutes. Then, operate the brake pedal with approximately 89N (20 lb) of force. The pedal feel (brake applications) should be the same as noted with the engine running. If the brake pedal feels hard (no power assist), install a new check valve and then repeat the testing. If the brake pedal stills feels hard, install a new brake booster. If the brake pedal movement feels spongy, bleed the brake system. REFER to: (206-00 Brake System - General Information)
Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures). Brake Master Cylinder NOTE:Before carrying out any diagnosis, make sure the brake system warning indicator is functional. Usually, the first and strongest indicator of anything wrong in the brake system is a feeling through the brake pedal. In diagnosing the condition of the brake master cylinder, check brake pedal feel as evidence of a brake concern. Check for brake warning indicator illumination and the brake fluid level in the brake fluid reservoir. Normal Conditions The following conditions are considered normal and are not indications that the brake master cylinder is in need of repair. - 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 of another vehicle, same model and year.
- During normal operation of the brake master cylinder, the brake fluid level in the reservoir will rise during brake application and fall during release. The net brake fluid level (after brake application and release) will remain unchanged.
- A trace of brake fluid exists on the brake booster shell below the master cylinder mounting flange. This results from the normal lubricating action of the master cylinder bore end seal.
- Brake fluid level will fall with brake pad and brake shoe wear.
Abnormal Conditions Changes in brake pedal feel or travel are indicators that something could be wrong in the brake system. The diagnostic procedure and techniques are brake pedal feel, brake warning indicator illumination and low 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 repair. - 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 or feels spongy. This condition may be caused by no fluid in the brake master cylinder reservoir, brake fluid reservoir cap vent holes blocked or air in the hydraulic system.
- Brake pedal effort is excessive. This may be caused by a bind or obstruction in pedal or linkage, blocked fluid control valve or insufficient brake booster vacuum.
- Rear brakes lock up during light pedal force. This may be caused by grease or fluid on brake shoes, damaged brake shoes and linings, incorrectly adjusted parking brakes, damaged, contaminated brake pressure control valve.
- Brake pedal effort is erratic. This condition could be caused by the brake booster being in operative, extreme brake caliper piston knock back or incorrectly installed brake shoes.
- Brake warning indicator is always ON. This may be caused by low fluid level, ignition wire routing too close to the fluid level indicator, or float assembly damage.
Bypass Condition Test - Check the brake fluid level in the brake fluid reservoir. Fill the brake fluid reservoir to the MAX mark if low or empty.
- Observe the brake fluid level in the brake fluid reservoir. If after several brake applications, the brake fluid level remains the same, measure the wheel turning torque required to rotate the wheels with rearward with brakes applied as follows:
- Place the transmission in NEUTRAL and raise and support the vehicle.
REFER to: Lifting (100-02 Jacking and Lifting, Description and Operation).
- Operate the brakes with a minimum of 445 N (100 lb) and hold for approximately 15 seconds. With the brakes still applied, exert torque on the front wheels to 10.1 Nm (75 lbf-ft). If either wheel rotates, install a new brake master cylinder.
Non-Pressure Leaks Any empty brake fluid reservoir condition may be the result of two types of non-pressure external leaks. - Type 1: An external leak may occur at the brake fluid reservoir cap because of incorrect positioning of the gasket and cap. Repair such a leak by repositioning the gasket and cap.
- Type 2: An external leak may occur at the brake fluid reservoir mounting seals. Repair such a leak by installing new seals.
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