Poor braking effectiveness indicates not only the case where the brake does not operate at all even when the brake pedal is depressed, but also the case where the brake effectiveness is weak against the depressing force or there is no pedal feel. When troubleshooting poor braking effectiveness, it is vital to have a thorough compensation of the technical aspects in order to understand why the braking effectiveness worsens.
Poor braking effectiveness mainly occurs under the following conditions.
1. When there is a malfunction in the brake system
2. When the vacuum pressure in the brake booster is not maintained
3. When fade phenomenon or vapor lock occurs
4. When the vehicle gross weight is increased due to passengers or laden weight
5. When driving on a submerged road
6. When the friction coefficient changes between the tire and the road surface
Poor Braking Effectiveness
1. In the case when there is a malfunction in the brake system
Trouble in the brake system usually occurs in the rubber parts of the hydraulic system such as the brake hose, the piston cup, etc. Long -term use of the rubber parts in the system results in deterioration, which causes fluid leakage. Moreover, emergency braking may result in a deteriorated part bursting suddenly, causing the braking system to lose control. There are two brake hydraulic systems in the brake system concerning safety. However, when either of these systems have a malfunction, braking will be affected.
2. When the vacuum pressure in the brake booster is not maintained
If the engine stalls while driving, the vacuum pressure in the booster is not maintained. Pressure in the booster is not secured. In this case, the brake functions correctly only once. The brake pedal will feel heavy and the brake seems to be ineffective after the second trial.
Even when the booster does not operate, it does not mean that the brake effectiveness is not gained. If the driver fully depresses the brake pedal, braking is effective although the deceleration rate is less than normal.
3. In the case where fade phenomenon or vapor lock occurs
Fade phenomenon
The resin contained in the friction materials of the pad and shoe produce gas when the temperature of the pad and shoe increases. Poor braking effect results if the gas that acts as a lubricant reduces the friction coefficient. The fade phenomenon tends to occur especially during the initial period because the pad and shoe contains appropriate conditions for producing the gas.
Poor Braking Effectiveness
The thermal history can be checked by disassembling the brake unit responsible for the fade phenomenon.
Vapor lock
The driver doesn’t feel any reaction from the brake pedal and the braking effect is reduced when bubbles occur in the brake fluid. The bubbles are produced when the heat in the pad and shoe is transferred to the brake fluid and the fluid boils.
Conditions causing vapor lock
• After stopping a vehicle, the brake unit is not cooled down by
sufficient airflow.
• The brake fluid is not changed for a long time.
Be sure to remove the air from the fluid. Once the vapor lock occurs, bubbles remain in the piping although the brake pedal operating force returns to normal after the brake cools down.
4. In the case where the vehicle gross weight is increased due to passengers or laden weight
As the vehicle weight becomes heavier, stopping inertia becomes greater. The stopping distance will be longer even if the brake pedal is depressed with the same force.
5. In the case where driving on a submerged road
Temporary poor braking effect is caused by the low friction coefficient due to the lubricating action of the water when the friction material in the brake becomes wet. Repeated braking allows the water to evaporate and regain the braking effect with friction heat.
6. When the friction coefficient changes between the tire
and road surface
Tires tend to slip and the stopping distance becomes longer when running on a wet or snow covered road or using worn tires. If emergency braking is applied under such conditions, tires will lock and make the vehicle unstable resulting in a spin.
Braking and Pedal Operating Force Check
1. Maximum braking force check
Measure braking force using a brake tester
Criteria
There must be no difference when comparing with another vehicle of the same model.
2. Compare the breaking force and pedal operating force
Measure the breaking force and pedal operating force using a pedal effort meter and brake tester.
Criteria
There must be no difference when comparing with another vehicle of the same model.