Road Test Quick Checks

1. 24-80 km/h (15-50 mph): With light acceleration. a moaning noise is heard and possibly a vibration is felt in the floorpan. It is usually worse at a particular engine speed and at a particular throttle setting during acceleration at that speed. It may also produce a moaning sound, depending on what component is causing it. Refer to Tip-in Moan in Symptom Chart. B: Tip-In Moan
2. 40-72 km/h (25-45 mph): With steady to heavy acceleration or deceleration, a ramble-type noise is heard. It is very intense during heavy acceleration or deceleration and very light during cruise or neutral coast. The vibration is hard to duplicate with vehicle supported on a hoist because wheels are coasting free. Refer to Idle Boom/Shake/Vibration in Symptom Chart. C: Idle Boom/Shake/Vibration
3. High Speed: With slow acceleration and deceleration or at constant speed, a shake is sometimes noticed in the steering wheel / column, seats, floorpan, trim panels 9r front end sheet metal. It is a low frequency vibration (around 9-15 cycles per second). It may or may not be increased by applying brakes lightly. Refer to High Speed Shake in Symptom Chart. A: High Speed Shake
4. High Speed: A vibration is felt in the floorpan or seats with no visible shake, but with an accompanying sound or rumble, buzz, hum, drone or booming noise.
It will exist in all drive modes, but may vary somewhat in acceleration, deceleration, float or coast modes. In some cases, the driveline vibration is eliminated in the float mode. Refer to Driveshaft Vibration in Symptom Chart. E: Driveshaft Vibration
5. 0-High Speed: A vibration is felt whenever the engine reaches a particular rpm. The vibration can be duplicated by operating the engine at the problem rpm while the vehicle is sitting still. It can be caused by any component from the fan back to the torque converter and by anything that turns at engine speed when the vehicle is stopped. Refer to Engine Accessory Vibration in Symptom Chart. D: Engine Accessory Vibration

Road Conditions
The road is an important factor in the road test and a smooth asphalt road that allows driving over a range of speeds is best. The brushed concrete road surface found on many expressways and the coarse aggregate sometimes found in concrete can mask many vehicle noises and make diagnosis difficult.
If the customer complains of a noise or vibration on a particular road and only on a particular road, the source of the concern may be the road surface. If possible, try to test on the same type of surface. This is the only case where a smooth asphalt road may not be the best.

Vehicle Preparation
1. Check and verify if vehicle is equipped with original equipment, type, size and brand wheels and tires. If non-original equipment wheels or tires are installed, it may be necessary to substitute original equipment level tire / wheel assemblies for diagnosis.
2. Check and set tire pressure.

Hoist Test
NOTE: A test on the hoist may produce different vibrations and noises than a road test because of the effect of the hoist on the rear axle. It is not unusual to find vibrations on the hoist that were not found in the road test and many times these may be ignored. If the condition that was found on the road can be duplicated on the hoist, performing experiments on the hoist may save a great deal of time.

After a road test, it is sometimes. useful to do a similar test on a hoist.
1. Elevate the rear wheels slightly, check to make sure that both are turning and run the engine up with the vehicle in gear.

NOTE: Use an axle hoist instead of a frame hoist. An axle hoist will not change the driveline angles. Use a frame hoist and use axle stands.

2. Explore the speed range of interest using the drive/cruise/coast/float tests.
3. Perform a coast down in NEUTRAL. If the vehicle is free of vibration when operating at a steady indicated speed and behaves very differently in drive and coast, an axle concern is likely.