Many claims these days suggest that automotive brake failure directly contributed to an accident. For those losses where brake malfunction is a suspected cause, the claims investigator is obliged to look into the existence of evidence of brake failure.

Figure 1 to the right offers a brief review of an automobile brake system. The brake pedal presses against a vacuum assist brake booster that pushes on a master hydraulic cylinder, resulting in increased hydraulic pressure in brake lines. The brake lines are connected to brake calipers or brake shoe wheel cylinders, causing increased friction on the brake drum or rotor, resulting in vehicle braking.

Older vehicle master cylinders supply hydraulic pressure to all brakes via one brake line (arrow Figure 2). Unfortunately, if a leak occurs in a brake line, then the whole system loses pressure, and fails. Modern brakes have dual master cylinders that operate two independent systems, which have proven more reliable. Modern brake systems are also equipped with anti-lock features that have improved performance on certain road surfaces.

Figure 3 is a case study where the insured claimed that the brakes failed, causing an accident. The vehicle was an older pickup truck with a single brake system master cylinder. In Figure 3, corrosion has thinned the wall of the brake tube, leading to brake tube failure, and brake fluid leakage, ultimately causing brake failure. This is a maintenance-related malfunction. In a dual master cylinder system, this tube failure would result in an approximately 50-percent loss of braking capacity, while hard braking capacity would be lost altogether.

Figures 4A and 4B to the right illustrate a failure where the entire master cylinder broke loose from the engine vacuum assist brake booster. The insured claimed brake failure, which resulted in relatively minor impact damage to the vehicle, as shown in Figure 4A. Examination of the brake system revealed that the master cylinder had parted from the brake booster in a manner such that when the brake pedal was pressed, no actual braking occurred. The damage to the vehicle did not support the conclusion that the impact caused the failure of the master cylinder or the brake booster connection. Further examination of the brake system revealed a tool mark on the master cylinder housing shown in Figure 4B. Apparently, during a recent repair of the vehicle, the individual performing the work used the master cylinder body as a pry point, causing damage that lead to failure. This is an example of an improper repair causing an accident.

Figure 5 below is a view of a brake line wrapped in a small thermal insulator, which had been recently installed as a result of a recall to protect the brake line from exhaust pipe heat. Evidence suggests that during installation of the insulator, the brake tubing was bent and began to leak shortly afterward, resulting in deficient braking. An accident can thus be attributed to improper repair of this vehicle.

Some vehicles are equipped with a brake assist pump that operates when the brake pedal is pressed. Typically, a relay senses a signal that the brakes are applied and activates the brake assist pump, which aids in braking. One accident occurred as a result of deficient braking where a light truck struck another vehicle. The brake assist pump system was not operational, which resulted in a loss of braking capacity of the vehicle. Figure 6A shows the relay that engaged the pump assist system. The relay module was intermittent in operation. X-ray analysis shows that one of the connector blades was significantly out of position as shown in Figure 6B.

Figure 6A also shows the blade in the wrong position. This prevented the blade from being inserted fully into the receptacle, causing intermittent operation and intermittent brake failure. The retracted blade appears to be a result of a manufacturing defect.


Another case study where brakes failed, causing an accident, revolves around degradation of brake system hydraulic seals. Upon examination of the vehicle, all caliper seals had failed with severe brake leakage. The master cylinder reservoir cap seals were found to be swollen, as shown in Figure 7. Such a condition usually results from using a fluid other than brake fluid in the hydraulic system. In this particular case, the automotive repair person mistakenly introduced power steering fluid into the brake system. This caused rapid deterioration of the polymer seals, which were not designed for such a fluid.

A Common Scenario
Parking brakes can be at the root of many claims. A typical scenario is the loading of a vehicle on a slope with the parking brake engaged, but not the standard transmission. As the vehicle is being loaded, it starts to roll down the hill, causing an accident. Static friction, which exists when the parking brake is set and the vehicle is not rolling, is quite high. When the vehicle begins to roll, there is dynamic friction, which is less than the static friction and the vehicle typically tends to accelerate. A common cause of this is improper adjustment of the parking brake.

Figure 8 is a view of a parking brake adjuster on a pickup truck that was not properly adjusted. Figure 9 is a view of a driveshaft parking brake that was not properly adjusted. Each resulted in a roll away during loading, causing an accident. When parking, it is good practice to engage the transmission on standard transmission vehicles. Automatic transmission vehicles have a park position that is typically engaged when parking.

Brake failure claims may necessitate an inspection of the vehicle. If the vehicle is drivable, then a road test can yield insight into any existing deficiencies. If the vehicle cannot be driven, then component testing, such as testing individual brake lines or master cylinder, may be required.

Some deficient brake claims may be a result of road conditions and not a deficiency in the vehicle brake system. Bald tires on wet pavement can cause subpar braking. Likewise, modern anti-lock brake systems do not work as well as conventional brake systems on gravel surfaces.