Glossary of Terms
AccelerationThe act or process of increasing speed. Acceleration occurs at light, medium, or Wide-open Throttle (WOT) conditions.
Light Acceleration
An increase in speed at less than half throttle.
Medium Acceleration
An increase in speed at half to nearly full throttle.
WOT Acceleration
An increase in speed at wide-open throttle.
Ambient Temperature
The surrounding or prevailing temperature.
Articulation
The relative movement of attached components.
Belt Chirp
A high-pitched short-duration noise usually caused by belt misalignment.
Belt Squeal
A high-pitched long-duration noise usually caused by belt slippage.
Boom
A low-frequency (sometimes cycling) noise, often felt as well as heard.
Bound Up
A stressed isolation mount or component that transmits vibration instead of dampening or isolating it.
Brakes Applied
The use of the brakes to keep the vehicle from moving.
Camber
The angle of the wheel in relation to the true vertical as measured looking from the front of the vehicle. Camber is positive when the wheel angle is offset so that the top of the wheel is positioned away from the vehicle.
Caster
The angle of the steering knuckle in relation to the true vertical as measured looking from the side of the vehicle.
Chuckle
The noise that occurs during the coast driving phase, usually caused by excessive clearance due to differential gear wear or by a damaged tooth on the coast side of the final drive ring gear.
Clunk
A short-duration, dull sound, usually associated with the transmission engaging in reverse or drive, or heard upon initial drive-away.
Coast/Deceleration
The vehicle is in motion and the transmission is engaged, but no pressure is applied to the accelerator pedal. Speed control, if equipped, is disengaged.
Coast/Neutral Coast
The vehicle is in motion with the transmission disengaged.
Controlled Rear Suspension Height
The height that a designated vehicle element must be at when driveline angle measurements are made.
Coupling Shaft
The front shaft in a two-piece driveline system.
CPS
Cycles per second.
Cruise
Constant speed on level ground; neither accelerating nor decelerating.
Deceleration
Slowing of the vehicle by releasing the accelerator pedal, but without using the brakes.
Drive Engine Run-Up Test
The operation of the engine through the normal rpm range with the vehicle standing still and the transmission engaged. This test is used for 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 axle input shaft (pinion shaft). In a two-piece driveline, it is the rearmost shaft.
Dynamic Balance
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.
Drivetrain
All power transmitting components from the engine to the wheels; includes the clutch or torque converter, the transmission, the driveline, and the 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.
Dynamic Balance
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
An exaggerated engine movement or vibration that directly increases in frequency as the engine speed increases.
Engine Shake
A condition in which an engine's mass center is not concentric to the rotation center.
Engine Misfire
When ignition in one or more cylinders does not occur or occurs at the wrong time.
Flexible Coupling
A flexible joint in the exhaust pipe located between the catalytic converter and muffler, designed to eliminate binding conditions in the exhaust system and eliminate exhaust NVH.
Float
A drive mode on the dividing line between cruise and coast where the throttle setting matches the engine speed with the road speed.
Gravelly Feel
A grinding or growl in a component, similar to the feel experienced when driving on gravel.
Harshness
A firmer-than-usual response of a component.
Hose Clamp
A screw-type circular clamp.
Hz
Hertz; a frequency of one cycle per second.
Imbalance
Out of balance; heavier on one side than the other. In a rotating component, imbalance often causes vibration.
Inboard
Toward the vehicle centerline.
In-Phase
The in-line relationship between the forward coupling haft yoke and the driveshaft centering socket yoke of a two-piece driveline.
Isolate
To separate from the influence of other components.
Knock
The noise caused by gear tooth damage on the drive side of the final drive ring gear, and also by the relative motion of components that are supported by bearings.
Neutral Engine Run-Up 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 relieve stress from possible bound-up components.
NVH
Noise, vibration and harshness.
Outboard
Away from the centerline of the vehicle.
Pinion Shaft
The input shaft in a driving axle that is usually a part of the smaller driving or input hypoid gear of a ring and pinion gearset.
Pumping Feel
A slow pulsing movement.
Radial/Lateral
Radial is in the plane of rotation; lateral is at 90 degrees to the plane of rotation.
Ring Gear
The large, circular, driven gear in a ring and pinion gearset.
Road Test
The operation of the vehicle under conditions intended to produce the concern under investigation.
Runout
Out of round or wobble.
Shake
Low frequency vibration, usually with visible movement.
Slip Yoke/Slip Spline
The driveshaft coupling that allows length changes to occur while the suspension articulates and while the driveshaft rotates.
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.
Tip-In Moan
A light moaning noise heard during light vehicle acceleration, usually between 40-100 km/h (25-65 mph).
TIR
Total indicated runout.
Tire Deflection
The change in tire diameter in the area where the tire contacts the ground.
Tire Force Vibration
A tire vibration caused by variations in the construction of the tire that is noticeable when the tire rotates against the pavement. This condition may be present on perfectly round tires because of variations in the inner tire construction.
Tire Flat Spots
A condition commonly caused by letting the vehicle stand when the tires are warm. It can be corrected by driving the vehicle until the tires are warm. This concern is more likely to occur with N, V and Z-speed rated tires.
Tire wear caused by wheel-locked skids.
Two-Plane Balance
Radial and lateral balance.
Vibration
An unwanted periodic motion of a body or medium. It can be felt, heard or seen.