Glossary of Terms Used In Pinpoint Tests
ACCELERATIONLight
Part throttle increase in speed such as 0-97 km/h (0-60 mph) in approximately 30 seconds.
Heavy
One-half to full throttle increase in speed such as 0-97 km/h (0-60 mph) in approximately 20 seconds.
WOT
Wide open throttle.
Ambient Temperature
Surrounding or prevailing temperature. Normally the temperature in the service area or outdoors, depending on where the testing is taking place.
Articulation
Vertical movement of the front driving or rear axle.
Belt Chirp
An intermittent noise usually at idle caused by belt misalignment.
Belt Squeal
A continuous noise by a frozen accessory or insufficient tension.
Boom
A cycling, low frequency rhythmic noise often accompanied by a sensation of pressure on the ear drums.
Bound Up
Refers to a stressed, rubber-mounted component that transmits any NVH which would normally be absorbed by the mount. Refer to Neutralize.
Brakes Applied
When vehicle is stationary, service brakes applied with enough force to hold vehicle against acceleration with transmission in gear.
Camber
Angle formed between front wheel spindle axis and horizontal as viewed from in front of the vehicle.
Camber is positive when the wheel tops are farther apart than the wheel bottoms.
Caster
Angle formed between the front suspension lower arm centerline axis and a vertical axis as viewed from the side of the vehicle. Caster is considered positive when the top of the kingpin axis is behind the vertical axis.
Chuckle
Refers to the noise that occurs on 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 or pinion gear.
Clunk
Due to excessive ring gear backlash, elongation of the differential pinion shaft holes in the differential case, or missing side gear or pinion gear thrust washers. If none of these conditions exist, clunk may be caused by a loose fit of the front wheel drive shaft joints to the side gear splines.
Coast/Deceleration
Slowing of vehicle by releasing foot from accelerator pedal at cruise and allowing engine to slow vehicle without application of brakes.
Coast/Neutral Coast
Engine/transmission taken out of gear with driveshaft/driveline by placing transmission range selector in NEUTRAL or by depressing clutch in manual transmission.
Controlled Rear Suspension Height
The height at which the components of a particular vehicle should be set when driveline angle measurements are made.
CPS
Cycles Per Second (Hz).
Cruise
Steady highway speed; neither accelerating nor decelerating; even pressure on accelerator pedal on level ground.
Deceleration
Slowing of vehicle by releasing foot from accelerator pedal at cruise and allowing engine to slow vehicle without application of brakes.
Driveline Angles
Difference of alignment between the transmission output shaft, driveshaft and rear axle pinion centerline.
Driveshaft
Rearmost shaft of a driveline which powers the rear axle input shaft (pinion shaft).
Drivetrain
Includes all power transmitting components from the rear of the engine to the wheels, including clutch/torque converter, transmission, driveline and rear driving axles.
Drivetrain Damper
A counterweight attached to an arm on the rear of the transmission extension housing and designed to "soak up" or damp unwanted driveline or powertrain vibrations.
Engine Imbalance
Some component in the engine which is normally smoothly balanced now causing a perceptible vibration in the vehicle.
Engine Misfire
One or more cylinders in the engine fail to fire at the proper time.
Engine Runup Test
Operation of engine through normal rpm range while vehicle is sitting still. Used for engine vibration check.
Float
A cruising drive mode in which throttle setting matches engine speed to road speed between cruise and coast.
Gravelly Feel
A grinding or growl in a component, similar to the feel experienced while driving on gravel.
Harshness
A harder than usual behavior of a component, like riding a vehicle with overinflated tires.
Heavy Brake Applies
Firm brake pedal pressure pending lock-up.
Hose Clamp
Screw-type hose clamp.
Hz
Hertz (Cycles Per Second).
Imbalance
Out of balance; more weight on one side of a rotating component causing shake or vibration.
Inboard
Toward the centerline of the vehicle.
Isolate
Separate from the influence of other components.
Knock
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.
Knock, which can occur on all driving phases, has several causes. In most cases, one of the following conditions has occurred:
A gear tooth damaged on the drive side is a common cause of the knock. This can usually be corrected by grinding the damaged area.
NOTE: Be sure to measure the end play with a dial indicator, not by feel. A guess usually feels like far more end play than there actually is.
Knock is also characteristic of excessive end play in the axle shaft. Up to 0.762 mm (0.030 inch) is allowed in most axles. The frequency of knock will be less because the axle shaft speed is slower than the driveshaft.
Light Brake Applies
Enough brake pedal pressure to just begin to slow vehicle while off the accelerator.
Neutralize (Normalize)
To return to unstressed position. Used to describe mounts. Refer to Bound Up.
NVH
Noise, vibration, harshness.
Outboard
Toward the outside of the vehicle, rather than toward the centerline.
Pinion Shaft
The input shaft to a driving axle is usually a part of the smaller driving or input hypoid gear of a ring and pinion gearset.
Pumping Feel
Very slow vibration that results in a movement of vehicle components similar to pumping the service brakes slightly.
Radial/Lateral
Radial is in the plane of rotation, while lateral is at 90 degrees to the fore-and-aft plane of the vehicle.
Ring Gear
A large bevel gear driven by the pinion gear of a ring and pinion driving axle gearset.
Road Test
Operation of vehicle under conditions designed to recreate the condition.
Runout
Out-of-round or wobble.
Shake
Low frequency vibration, most noticeably results in visual movement of components such as the seat and steering wheel.
Slip Yoke (Slip Spline)
Driveshaft coupling device which compensates for changes in the shaft length due to movement of the axle or transmission used at one end of driveshaft.
Tip-In Moan
A light moaning noise is heard when the vehicle is moderately accelerated between 40-64 km/h (25-40 mph).
TIR
Total indicator runout.
Tire Deflection
Bending of the body of the tire during rotation.
Tire Force Vibration
Tire vibrations caused by variations in the construction of the tire, resulting in a vibration when the tire rotates against the pavement. This condition may be present on perfectly round tires because of variations in the inner construction. May occur at wheel rotation frequency or twice rotation frequency.
Tires-Flat Spots
Commonly caused by letting vehicle stand when tires are warm. Can be cured by operating vehicle until tires are warm. This concern is more likely to occur with H, V and Z-speed rated tires.
Two-Plane Balance
Balance of two parallel planes of a rotating component.
Vibration
Regular movement of a component that results in a sound or feel of movement.
Typical vibration frequencies, measured in cycles per second, (Hz) are:
- Engine accessories (up to 160 Hz) (usually caused by engine firing pulses).
- Engine (40 Hz); firing (80 Hz) (engine firing frequency depends on the number of cylinders).
- Pinion (40Hz); ring gear (13Hz).
- Wheels and tires (13 Hz).
- Driveshaft (40 Hz); rear axle shaft universal joint (80 Hz). The vehicle normally responds to a certain driveline frequency. If the rear axle shaft universal joints are the source, the condition will occur at one-half the speed of a typical high speed driveline concern.
- Wheel bearings (6 Hz).