Jaguar XJ (X350). Manual — part 37

•

suspension

•

driveline

•

air leakage (wind noise)

•

squeaks and rattles

•

heating ventilation and air conditioning (HVAC)

•

electrical (e.g. motor noise)

•

transmission

•

engine

It is important, therefore, that an NVH concern be isolated into its specific area(s) as soon as
possible. The easiest and quickest way to do this is to carry out the Road Test as outlined.

Noise Diagnostic Procedure

Non-Axle Noise

The five most important sources of non-axle noise are exhaust, tires, roof racks, trim and
mouldings, and transmission.

Therefore, make sure that none of the following conditions are the cause of the noise before
proceeding with a driveline teardown and diagnosis.

•

In certain conditions, the pitch of the exhaust may sound very much like gear noise. At
other times, it can be mistaken for a wheel bearing rumble.

•

Tires, especially snow tires, can have a high pitched tread whine or roar, similar to
gear noise. Radial tires, to some degree, have this characteristic. Also, any non-
standard tire with an unusual tread construction may emit a roar or whine type noise.

•

Trim and mouldings can also cause whistling or a whining noise.

•

Clunk may be a metallic noise heard when the automatic transmission is engaged in
reverse or drive, or it may occur when the throttle is applied or released. It is caused
by backlash somewhere in the driveline.

•

Bearing rumble sounds like marbles being tumbled. This condition is usually caused
by a damaged wheel bearing.

Noise Conditions

•

Gear noise is typically a howling or whining due to gear damage or incorrect bearing
preload. It can occur at various speeds and driving conditions, or it can be continuous.

•

Chuckle is a particular rattling noise that sounds like a stick against the spokes of a
spinning bicycle wheel. It occurs while decelerating from 64 km/h (40 miles/h) and
can usually be heard all the way to a stop. The frequency varies with vehicle speed.

•

Knock is very similar to chuckle, though it may be louder and occurs on acceleration
or deceleration. The teardown will disclose what has to be corrected.

Check and rule out tires, exhaust and trim items before disassembling the transmission to
diagnose and correct gear noise.

The noises described under Road Test usually have specific causes that can be diagnosed by

observation as the unit is disassembled. The initial clues are the type of noise heard on the
road test and the driving conditions.

Vibration Conditions

NOTE:

New Constant Velocity (CV) joints should not be installed unless disassembly and
inspection revealed unusual wear.

Clicking, popping or grinding noises may be caused by the following:

•

Cut or damaged CV joint boots resulting in inadequate or contaminated lubricant in
the outboard or inboard CV joint bearing housings

•

Loose CV joint boot clamps

•

Another component contacting the rear drive half shaft

•

Worn, damaged or incorrectly installed wheel bearing, suspension or brake component

Vibration at highway speeds may be caused by the following:

•

Out-of-balance front or rear wheels

•

Out-of-round tires

•

Driveline imbalance

•

Driveline run-out (alignment)

NOTE:

Rear drive half shafts are not balanced and do not contribute to rotational vibration
disturbances.

Shudder or vibration during acceleration may be caused by the following:

•

Excessively worn or damaged outboard or inboard CV joint bearing housing

•

Excessively high CV joint operating angles caused by incorrect ride height. Check ride
height, verify correct spring rate and check items under Inoperative Conditions

Leakage Conditions

1 . Inspect the CV joint boots for evidence of cracks, tears or splits.

2 . Inspect the underbody for any indication of grease splatter in the vicinity of the rear drive
half shaft, outboard and inboard CV joint boot locations, which is an indication of CV joint
boot or CV joint boot clamp damage.

3 . Inspect the inboard CV joint bearing housing seal for leakage.

Inoperative Conditions

If a CV joint or rear drive half shaft pull-out occurs, check the following:

www.

•

suspension components for correct location, damage or wear

•

bushings for wear

•

subframe for damage

•

bent or worn components Stabilizer bar link Left-hand rear suspension lower arm and
bushing Right-hand rear suspension lower arm and bushing Rear wheel hub and rear
drive half shaft

Road Test

A gear-driven unit will produce a certain amount of noise. Some noise is acceptable and may
be audible at certain speeds or under various driving conditions as on a newly paved blacktop
road. The slight noise is in no way detrimental and must be considered normal.

The road test and customer interview (if available) provide information needed to identify the
condition and give direction to the correct starting point for diagnosis.

1 . Make notes throughout the diagnosis routine. Make sure to write down even the smallest
piece of information, because it may turn out to be the most important.

2 . Do not touch anything until a road test and a thorough visual inspection of the vehicle have
been carried out. Leave the tire pressures and vehicle load just where they were when the
condition was first observed. Adjusting tire pressures, vehicle load or making other
adjustments may reduce the conditions intensity to a point where it cannot be identified
clearly. It may also inject something new into the system, preventing correct diagnosis.

3 . Make a visual inspection as part of the preliminary diagnosis routine, writing down
anything that does not look right. Note tire pressures, but do not adjust them yet. Note leaking
fluids, loose nuts and bolts, or bright spots where components may be rubbing against each
other. Check the luggage compartment for unusual loads.

4 . Road test the vehicle and define the condition by reproducing it several times during the
road test.

5 . Carry out the Road Test Quick Checks as soon as the condition is reproduced. This will
identify the correct diagnostic procedure. Carry out the Road Test Quick Checks more than
once to verify they are providing a valid result. Remember, the Road Test Quick Checks may
not tell where the concern is, but they will tell where it is not.

Road Test Quick Checks

1 . 24-80 km/h (15-50 miles/h): 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.

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.

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 the
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 discs, wheel hubs or front
wheel bearings. Refer to High Speed Shake in the Symptom Chart.

4 . Engine rpm Sensitive: A vibration is felt whenever the engine reaches a particular rpm. It
will disappear in neutral coasts. The vibration can be duplicated by operating the engine at the
problem rpm while the vehicle is stationary. 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 High Speed Shake in the Symptom Chart.

5 . Noise and Vibration While Turning: Clicking, popping, or grinding noises may be due to
the following:

•

Worn, damaged, or incorrectly installed front wheel bearing.

•

Worn or damaged incorrectly installed rear drive half shaft.

•

Air suspension fault due to low level of vehicle under certain road conditions wheels
may come into contact with the wheel arch liner.

Road Conditions

An experienced technician will always establish a route that will be used for all 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.

NOTE:

Some concerns may be apparent only on smooth asphalt roads.

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.

Vehicle Preparation

Carry out a thorough visual inspection of the vehicle before carrying out the road test. Note
anything which is unusual. Do not repair or adjust any condition until the road test is carried
out, 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.

www.