Clonk
A hydraulic knocking sound. Sound occurs with air pockets in a hydraulic system. Also described as
hammering.
Clunk/Driveline Clunk
A heavy or dull, short-
duration, low-frequency sound. Occurs mostly on a vehicle that is accelerating or
decelerating abruptly. Also described as a thunk.
Coast/Deceleration
Releasing the accelerator pedal at cruise, allowing the engine to reduce vehicle speed without
applying the brakes.
Coast/Neutral Coast
Placing the transmission range selector in NEUTRAL (N) or depressing the clutch pedal while at
cruise.
Constant Velocity (CV) Joint
A joint used to absorb vibrations caused by driving power being transmitted at an angle.
Controlled Rear Suspension Height
The height at which a designated vehicle element must be when driveline angle measurements are
made.
Coupling Shaft
The shaft between the transfer case and the front drive axle or, in a two- piece rear driveshaft, the front
section.
CPS
Cycles per second. Same as hertz (Hz).
Cracks
A mid- frequency sound, related to squeak. Sound varies with temperature conditions.
Creak
A metallic squeak.
Cruise
Constant speed on level ground; neither accelerating nor decelerating.
Cycle
The process of a vibrating component going through a complete range of motion and returning to the Klj . 4 ba
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starting point.
Decibel
A unit of measurement, referring to sound pressure level, abbreviated dB.
Drive Engine Run-
Up (DERU) Test
The operation of the engine through the normal rpm range with the vehicle standing still, the brakes
applied and the transmission engaged. This test is used for noise and vibration checks.
Driveline Angles
The differences of alignment between the transmission output shaft, the driveshaft, and the rear axle
pinion centerline.
Driveshaft
The shaft that transmits power to the rear axle input shaft (pinion shaft). In a two- piece driveshaft, it is
the rearmost shaft.
Drivetrain
All power transmitting components from the engine to the wheels; includes the clutch or torque
converter, the transmission, the transfer case, the driveshaft, and the front or rear drive axle.
Drivetrain Damper
A weight attached to the engine, the transmission, the transfer case, or the axle. It is tuned by weight
and placement to absorb vibration.
Drone
A low frequency (100- 200 Hz) steady sound, like a freezer compressor. Also described as a moan.
Drumming
A cycling, low-frequency (20- 100 Hz), rhythmic noise often accompanied by a sensation of pressure on
the ear drums. Also described as a low rumble, boom, or rolling thunder. Dynamic Balance Klj . 5 ba
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The equal distribution of weight on each side of the centerline, so that when the wheel and tire
assembly spins, there is no tendency for the assembly to move from side-
to-side (wobble).
Dynamically unbalanced wheel and tire assemblies can cause wheel shimmy.
Engine Imbalance
A condition in which an engine's center mass is not concentric to the rotation center, causing
excessive motion.
Engine Misfire
When combustion in one or more cylinders does not occur or occurs at the wrong time.
Engine Shake
An exaggerated engine movement or vibration that directly increases in frequency as the engine speed
increases. It is caused by non- equal distribution of mass in the rotating or reciprocating components.
Flexible Coupling
A flexible joint.
Float
A drive mode on the dividing line between cruise and coast where the throttle setting matches the
engine speed with the road speed.
Flutter
Mid to high (100- 2000 Hz) intermittent sound due to air flow. Similar to a flag flapping in the wind.
Frequency
The rate at which a cycle occurs within a given time.
Gravelly Feel
A grinding or growl in a component, similar to the feel experienced when driving on gravel.
Grind
An abrasive sound, similar to using a grinding wheel, or rubbing sand paper against wood.
Hiss
Steady high frequency (200- 800 Hz) noise. Vacuum leak sound.
Hoot
A steady low frequency tone (50- 500 Hz), sounds like blowing over a long neck bottle. Howl Klj . 6 ba
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A mid-
range frequency (200- 800 Hz) noise between drumming and whine. Also described as a hum.
Hum
Mid- frequency (200- 800 Hz) steady sound, like a small fan motor. Also described as a howl.
Hz
Hertz; a frequency measured in cycles per second.
Imbalance
Out of balance; heavier on one side than the other. In a rotating component, imbalance often causes
vibration.
Inboard
Toward the centerline of the vehicle.
Intensity
The physical quality of sound that relates to the strength of the vibration (measured in decibels). The
higher the sound's amplitude, the higher the intensity and vice versa.
Isolate
To separate the influence of one component to another.
Knock
A heavy, loud, repetitious sound, like a knock on the door.
Moan
A constant, low- frequency (100-200 Hz) tone. Also described as a hum.
Neutral Engine Run- Up (NERU) Test
The operation of the engine through the normal rpm range with the vehicle standing still and the
transmission disengaged. This test is used to identify engine related vibrations.
Neutralize/Normalize
To return to an unstressed position. Used to describe mounts. Refer to Bound Up.
Outboard
Away from the centerline of the vehicle.
Ping
A short duration, high- frequency sound, which has a slight echo. Klj . 7 ba
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Lateral runout means measuring the movement or "wobble" of a wheel or tire at the sidewall. Radial
runout means measuring the out-of-
round at the tread surface.
Rustling
Intermittent sound of varying frequency (100- 2000 Hz), sounds similar to shuffling through leaves.
Shake
A low- frequency vibration (5-20 Hz), usually with visible component movement. Usually relates to tires,
wheels, brake drums or brake discs if it is vehicle speed sensitive, or engine if it is engine speed
sensitive. Also referred to as a shimmy or wobble.
Shimmy
An abnormal vibration or wobbling, felt as a side- to-side motion of the steering wheel in the driveshaft
rotation. Also described as waddle.
Shudder
A low- frequency vibration that is felt through the steering wheel or seat during light brake application.
Slap
A resonance from flat surfaces, such as safety belt webbing or door trim panels.
Slip Yoke/Slip Spline
The driveshaft coupling that allows length changes to occur while the suspension articulates and while
the driveshaft rotates.
Squeak
A high- pitched transient sound, similar to rubbing fingers against a clean window.
Squeal
A long- duration, high- pitched noise.
Static Balance
The equal distribution of weight around the wheel. Statically unbalanced wheel and tire assemblies can
cause a bouncing action called wheel tramp. This condition will eventually cause uneven tire wear.
Tap
A light, rhythmic, or intermittent hammering sound, similar to tapping a pencil on a table edge.
Thump
A dull beat caused by two items striking together. Tick Klj . 9 ba
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WOT
The acronym for wide open throttle is WOT.
Tools and Techniques
Electronic Vibration Analyzer (EVA)
The EVA is a hand-
held electronic diagnostic tool which will assist in locating the source of
unacceptable vibrations. The vibration sensor can be remotely mounted anywhere in the vehicle for
testing purposes. The unit displays the three most common vibration frequencies and their
corresponding amplitudes simultaneously. A bar graph provides a visual reference of the relative
signal strength (amplitude) of each vibration being displayed and its relative G force. The keypad is
arranged to make the EVA simple to program and use. Some of the functions include the ability to
average readings as well as record, play back and freeze readings. The EVA has a strobe balancing
function that can be used to detect imbalance on rotating components such as a driveshaft or engine
accessories.
The EVA allows for a systematic collection of information that is necessary to accurately diagnose and
repair NVH problems. For the best results, carry out the test as follows:
a. Test drive the vehicle with the vibration sensor inside the vehicle.
b. Place the sensor in the vehicle according to feel. „If the condition is felt through the steering wheel, the source is most likely in the front of
the vehicle.
„ A vibration that is felt in the seat or floor only will most likely be found in the driveline,
drive axle or rear wheels and tires.
c. Record the readings. Also note when the condition begins, when it reaches maximum intensity, and if it tends to diminish above/below a certain speed.
„Frequencies should be read in the "average" mode. Item Description
1 EVA screen
2 Frequency mode displayed in rpm or Hz
3 Active sensor input (A or B)
4 Current active mode
5 G force indicators or the strongest frequencies in descending strength of each vibration
6 Strength of each vibration
7 Frequency in rpm/Hz of each vibration Klj . 11 ba
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