Buick Regal: Brake System Vehicle Road Test

Preliminary Inspections

1. Visually inspect easily accessible brake system components for obvious damage and/or leaks which may indicate that the vehicle should not be driven until further inspections have been completed.

2. Inspect the brake master cylinder reservoir fluid level and adjust only if necessary for brake system road testing. Brake Master Cylinder Reservoir Filling.

3. Inspect the tire inflation pressures and adjust as necessary.

4. Inspect the tire tread patterns to ensure that they are the same or very similar, especially per axle.

5. Ensure that the vehicle is not loaded unevenly prior to brake system road testing.

Road Testing Procedure

WARNING: Road test a vehicle under safe conditions and while obeying all traffic laws.

Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

1. Start the engine and allow it to idle.

2. Check to see if the brake system warning lamp remains illuminated.

3. If the brake system warning lamp remains illuminated, DO NOT proceed to test drive the vehicle until it is diagnosed and repaired.

4. Select a smooth, dry, clean and level road or large lot that is as free of traffic and obstacles as possible for brake system low speed road testing.

5. With the transmission in PARK, lightly apply the brake pedal. Observe both the pedal feel and the pedal travel.

6. If the brake pedal apply felt spongy, or the pedal travel was excessive, DO NOT drive the vehicle until it is repaired.

7. If the brake pedal apply did not feel spongy and the pedal travel was not excessive, proceed to step 8.

8. Release and apply the brakes.

9. While continuing to apply the brakes, shift the transmission into DRIVE, release the brakes and allow the engine to idle the vehicle away from the stopped position. Observe for a slow release of the brake system.

10. With the aid of an assistant to observe the vehicle's performance from outside of the vehicle, drive the vehicle at a low speed and lightly apply the brakes while driving past the assistant. Have the assistant observe for brake system noise from the side of the vehicle closest to them, while you observe both the pedal effort and the pedal travel.

11. If the brake pedal apply effort was excessive, or the pedal travel was excessive, DO NOT continue to test drive the vehicle until it is repaired.

12. If the brake pedal apply effort was not excessive and the pedal travel was not excessive, proceed to step 13.

13. Drive the vehicle in the opposite direction, at the same low speed and lightly apply the brakes while driving past the assistant. Have the assistant observe for brake system noise from the side of the vehicle closest to him.

14. Drive the vehicle at a low speed and shift the transmission into NEUTRAL without applying the brakes. Observe for a rapid deceleration in vehicle speed, indicating possible brake drag.

15. Select a smooth, dry, clean and level road that is as free of heavy traffic as possible for brake system moderate speed road testing.

16. Drive the vehicle at a moderate speed. Observe for a pull and/or incorrect tracking of the vehicle without the brakes applied.

17. While continuing to drive the vehicle at a moderate speed, perform several light applies of the brakes. Observe the pedal effort and the pedal travel, observe for brake system noise, pulsation and/or brake drag.

18. If the brake pedal apply effort was excessive, or the pedal travel was excessive, DO NOT continue to test drive the vehicle until it is repaired.

19. If the brake pedal apply effort was not excessive and the pedal travel was not excessive, proceed to step 20.

20. While continuing to drive the vehicle at a moderate speed, perform several moderate applies of the brakes. Observe the pedal effort and the pedal travel, observe for brake system pulsation and/or uneven braking action - either side to side, or front to rear.

A small amount of vehicle front end dip is expected during a moderate apply of the brakes.

21. If the brake pedal apply effort was excessive, or the pedal travel was excessive, DO NOT continue to test drive the vehicle until it is repaired.

BRAKE PEDAL TRAVEL MEASUREMENT AND INSPECTION

Special Tools

CH-28662 Brake Pedal Effort Gauge

For equivalent regional tools, refer to Special Tools.

1. With the ignition OFF and the brakes cool, apply the brakes 3-5 times, or until the brake pedal becomes firm, in order to deplete the brake booster power reserve.

2. Install the CH-28662 gauge to the brake pedal.

3.

Measure and record the distance (1) from the brake pedal to the rim of the steering wheel; note the points of measurement.

4. Apply and maintain the brakes with 445 N (100 lb F) of force to the brake pedal, as indicated on the CH-28662 gauge.

5. While maintaining 445 N (100 lb F) of force to the brake pedal, measure and record the distance (2) from the same point on the brake pedal to the same point on the rim of the steering wheel.

6. Release the brakes and repeat steps 3 and 4 to obtain a second measurement. After obtaining a second measurement, proceed to step 7.

7. Average the first and second measurements recorded during the two applies of the brakes.

8. Subtract the initial measurement, unapplied (1), from the averaged, applied measurement (2) to obtain the brake pedal travel distance.

BRAKE SYSTEM VACUUM SOURCE TEST

Special Tools

CH-558-A Pressure Gauge

For equivalent regional tools, refer to Special Tools

NOTE:

• Engine temperature, accessory load, and elevation level will affect engine vacuum.
• Vacuum readings will decrease by approximately 2.7 kPA (0.8 in Hg) for every 305 m (1000 ft) of elevation above sea level.

Definition

If the brakes on diesel engine vehicles are operated for a long period of time, e.g. when approaching traffic lights or a traffic jam, the vacuum may be used up. The pedal travel is shortened, but will quickly return to the original pedal travel once the vacuum has been built up. Drivers often describe this phenomenon as follows: "When the brakes are operated for a long time, the brake pedal goes right to the floor" and/or as "Spongy brake pedal". On diesel vehicles, this is no cause for concern, as the pressure in the brake system is rising at this point. This can be demonstrated by connecting CH- 558-A gauge (1) to the brake calliper.

NOTE: Ignition OFF.

1. Reduce negative air pressure in brake booster.

Press brake pedal repeatedly.

2. Check brake booster.

• Press down brake pedal and maintain pressure
• Start engine

Definition

The brake system is operating correctly if the brake pedal drops further. If the brake pedal does not drop further, the vacuum system (vacuum line, non-return valve) must be checked. If no fault can be found there, replace the power brake booster. Refer to Power Brake Booster Replacement.

BRAKE SYSTEM EXTERNAL LEAK INSPECTION

WARNING: Refer to Brake Fluid Irritant Warning.

CAUTION: Refer to Brake Fluid Effects on Paint and Electrical Components Caution.

1. In order to inspect for external brake fluid leaks, first check the fluid level in the master cylinder.

While a slight brake fluid level drop can be considered a normal condition due to brake lining wear, a very low level may indicate a brake fluid leak in the hydraulic system.

If the fluid level is abnormally low, adjust the brake fluid level.

2. Start the engine and allow it to idle.

3. Apply constant, moderate foot pressure to the brake pedal.

If the brake pedal gradually falls away while under foot pressure, there may be a brake fluid leak.

4. Turn OFF the ignition.

5. Visually inspect the following brake system components for brake fluid leaks, excessive corrosion, and damage. Give particular attention to all brake pipe and flexible hose connections to ensure that there are not any slight brake fluid leaks - even though the brake pedal may feel firm and hold steady:

• Master cylinder brake pipe fittings
• All brake pipe connections
• Brake pipes
• Brake hoses and connections
• Brake calipers and/or wheel cylinders, if equipped

6. While slight dampness around the master cylinder reservoir can be considered acceptable, brake fluid leaking from any of the brake system components requires immediate attention. If any of these components exhibit signs of brake fluid leakage, repair or replace those components. After the repair or replacement, reinspect the hydraulic brake system to assure proper function.

BRAKE SYSTEM INTERNAL LEAK TEST

WARNING: Refer to Brake Fluid Irritant Warning.

CAUTION: Refer to Brake Fluid Effects on Paint and Electrical Components Caution.

1. Start the engine and allow it to idle.

2. Apply light, steady pressure to the brake pedal. Observe both the brake pedal feel and travel.

3. Release the brakes and turn OFF the ignition.

4. If the brake pedal apply felt spongy, but the brake pedal travel was not excessive, perform the following steps:

1. Inspect the brake system for external leaks. Refer to Brake System External Leak Inspection.
2. Pressure bleed the brake system in order to purge any air that may be trapped in the system.

   Refer to Hydraulic Brake System Bleeding (Pressure) or Hydraulic Brake System Bleeding (Manual).

5.

If the brake pedal apply did not feel spongy, but the brake pedal travel was excessive, perform the following steps:

1. Loosen the master cylinder-to-brake power booster mounting nuts.
2. Carefully pull the master cylinder away from the brake power booster just enough to inspect the mounting surface of the master cylinder.
3. Inspect the master cylinder mounting surface at the primary piston (2) for brake fluid leaks.

6. If the master cylinder exhibits any leakage around the primary piston (2), then the primary piston primary seal (4) and/or secondary seal (3) is leaking and the master cylinder requires overhaul or replacement.

7. If the master cylinder primary piston (2) does not exhibit any leakage, pressure bleed the brake system. Refer to Hydraulic Brake System Bleeding (Pressure) or Hydraulic Brake System Bleeding (Manual).

8. If the brake pedal apply did not feel spongy, and the brake pedal travel was initially steady and not excessive, but then gradually fell, then the master cylinder requires overhaul or replacement due to an internal leak past the secondary piston (1) from the secondary piston primary seal (6) or secondary seal (5).

9. If the brake pedal apply did not feel spongy, and the brake pedal travel was initially steady and not excessive, then fell slightly, then became steady again, then the brake pressure modulator valve (BPMV) may be leaking internally, and may require replacement.

READ NEXT: