Road Tests

A road test is mandatory for any customer concern of noise or vibration that its not verified by the on-hoist check of chassis components. The Road Test Form is arranged to record the conditions that can be heard or felt during this test.

The Road Test Form lists four operating conditions or modes in which some axle noises come and go:
DRIVE: Accelerating the vehicle; a definite throttle depression applying engine torque.
CRUISE: Maintaining a constant speed with the throttle applied.
COAST: Decelerating with the throttle closed.
FLOAT: Controlled deceleration: backing the throttle continually to prevent either braking or accelerating torque from the engine.

It is important to operate the vehicle in all four modes and record those in which the noise occurs. The modes are defined in the preceding chart. Write down the kilometers-per-hour (miles-per-hour) range at which both noise and vibration occur. On vehicles equipped with overdrive transmissions, evaluate rear axle noise with the transmission in DIRECT DRIVE and not in OVERDRIVE. Transmission noise can be mistaken for rear axle noise when in OVERDRIVE.