Road Test

DESCRIPTION
A road test should be performed to compare actual vehicle braking performance with the performance standards expected by the driver. The ability of the test driver to make valid comparisons and detect performance deficiencies will depend on experience.

The driver should have a thorough knowledge of brake system operation and accepted general performance guidelines in order to make good comparisons and detect performance problems.

An experienced brake technician will always establish a route that will be used for all brake diagnosis road tests. The road selected will be reasonably smooth and level. Gravel or bumpy roads are not suitable because the surface does not allow the tires to grip the road equally. Crowned roads should be avoided because of the large amount of weight shifted to the low set of wheels on this type of road. Once the route is established and consistently used, the road surface variable can be eliminated from the test results.

ROAD TEST
The road test should begin with a general brake performance check. With the customer's description as a guide, the brake system should be tested at different vehicle speeds using both light and heavy brake pedal pressure. To determine if the problem is in the front or rear braking system, the service brake pedal is used first, then the parking brake. If the condition (i.e., pull, vibration, pulsation) occurs only with the parking brake, the problem is in the rear system. If the condition occurs when the service brake pedal is pressed, the problem is in the front system.

However, other causes such as wheel or suspension problems are not eliminated by this test.

Locking the brakes and sliding the tires should be avoided. Locked brakes and sliding tires do not indicate brake efficiency; a heavily braked and turning wheel will stop the vehicle in less distance than locked brakes. If the concern becomes evident during this check, it should be determined if it fits the description given before the road test. If the concern is not evident, an attempt should be made to duplicate the condition using the information from the description.

If a concern exists, the symptom chart in this section should be used to isolate a specific sub-system and condition description. From this description, a list of possible causes can be used to further narrow the cause to a specific component or condition. Symptom Chart(s)

A key factor in evaluating brake concerns is the deceleration rate. This varies from vehicle to vehicle and with changes in operating conditions. It is evident how well the brakes on a particular vehicle are working after just a few applications.