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 front floor pan. 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 the Symptom Chart. B: Tip-In Moan

2. Acceleration/Deceleration: With slow acceleration and deceleration, a shake is sometimes noticed in the steering wheel/column, seats, front floor pan, front door trim panel or 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 Idle Boom/Shake/Vibration in the Symptom Chart. C: Idle Boom/Shake/Vibration

3. High Speed: A vibration is felt in the front floor pan or seats with no visible shake, but with an accompanying sound or rumble, buzz, hum, drone or booming noise. Coast with clutch pedal depressed or shift control selector lever in NEUTRAL and engine idling. If vibration is still evident, it may be related to wheels, tires, front disc brake rotors, wheel hubs or front wheel bearing.

Refer to High Speed Shake in the Symptom Chart. A: High Speed Shake

4. Engine rpm Sensitive: A vibration is felt whenever the engine reaches a particular rpm. It will disappear in neutral coast. 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 accessory drive belt to the clutch or torque converter which turns at engine speed when the vehicle is stopped.

Refer to Engine Accessory Vibration in the Symptom Chart. D: Engine Accessory Vibration

5. Noise and Vibration While Turning: Clicking, popping, or grinding noises may be due to the following:
a. Cut or damaged front wheel driveshaft joint boot resulting in inadequate or contaminated lube fill in outboard front wheel driveshaft joint or inboard front wheel driveshaft joint.
b. Loose front wheel driveshaft joint boot clamp.
c. Other component contacting halfshaft assembly.
d. Worn, damaged or improperly installed front wheel bearing.
e. Worn, contaminated, or dry inboard front wheel driveshaft joint or outboard front wheel driveshaft joint.

ROAD CONDITIONS
An experienced technician will always establish a route that will be used for all Noise, Vibration and Harshness (NVH) diagnosis road tests. The road selected should be reasonably smooth, level and free of undulations (unless a particular condition needs to be identified). A smooth asphalt road that allows driving over a range of speeds is best. Gravel or bumpy roads are unsuitable because of the additional road noise produced. Once the route is established and consistently used, the road noise variable is eliminated from the test results.

If a 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 the vehicle on the same type of road. This is the only case where a smooth asphalt road may not be best.

VEHICLE PREPARATION
Perform a thorough visual inspection of the vehicle before performing the road test. Note anything which is unusual. Do not service or adjust any condition until the road test is performed, unless the vehicle is inoperative or the condition could pose a hazard to the technician.

After verifying the condition has been corrected, make sure all components removed have been installed.







HOIST TEST
After a road test, it is sometimes useful to do a similar test on a hoist.
1. Raise vehicle on hoist. Support suspension in normal ride height position with jackstands.
2. Explore the speed range of interest using the Road Test Quick Checks.
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, a transaxle concern is likely.

Note, however, that a test on the hoist may produce different vibrations and noises than a road test because of the effect of the hoist. It is not unusual to find vibrations on the hoist that were not found in the road test. If the condition found on the road can be duplicated on the hoist, performing experiments on the hoist may save a great deal of time.

NOTE: Some concerns may be apparent only on smooth asphalt roads.

When performing the high-speed shake diagnosis or engine accessory vibration diagnosis on a hoist, observe the following precautions:

WARNING: IF ONLY ONE DRIVE WHEEL IS ALLOWED TO ROTATE, SPEED MUST BE LIMITED TO 55 KM/H (35 MPH) INDICATED ON THE SPEEDOMETER SINCE ACTUAL WHEEL SPEED WILL BE TWICE THAT INDICATED ON THE SPEEDOMETER. SPEED EXCEEDING 55 KM/H (35 MPH) OR ALLOWING THE DRIVE WHEEL TO HANG UNSUPPORTED COULD RESULT IN TIRE DISINTEGRATION, DIFFERENTIAL FAILURE AND/OR CONSTANT VELOCITY JOINT AND HALFSHAFT FAILURE, WHICH COULD CAUSE SERIOUS PERSONAL INJURY AND EXTENSIVE VEHICLE DAMAGE.

CAUTION: The suspension should not be allowed to hang free. When the constant velocity joint is run at a very high angle, extra vibrations as well as damage to seals and joints can occur.

The front suspension lower arm should be supported as far outboard as possible. To bring the vehicle to its proper ride height, the full weight of the vehicle should be supported in front by floor jacks.