Noise or Vibration, Four-Wheel Drive Vehicles
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Noise, defined as any unpleasant sound, may be described in a variety of ways such as tapping, chirping, squealing, whistling, buzzing, humming, clunking or booming. You can associate these various descriptions of noise with a probable cause. Based on experience, these descriptions will assist in isolating the problem and correcting it. Generally recognizable problem areas are engine, drivetrain, wind and road surface noises. Other less obvious areas that should be considered as noise problem sources are any of the problems that cause the vibrations described in this section.
Noise Acceptability
A gear driven unit, especially a drive axle, will produce a certain amount of noise. Some noise is acceptable and may be audible at certain speeds or under various driving conditions: for example, tire noise on a newly paved blacktop road. Such noise is in no way detrimental to the operation of the vehicle and must be considered normal.
Also, Traction-Lok or Limited-Slip axles may produce a slight chatter on slow turns after extended highway driving, which is normal.
Noise from the transfer case in four-wheel drive may be the result of transfer case chain noise. This noise may take the form of a high or low frequency whine or growl and is normal in four-wheel drive vehicles. The noise is most pronounced when driving on hard surfaced roads in four-wheel drive and is due to driveline binding between the front and rear axles causing the chain to contact the front or rear of the sprocket teeth depending on whether the vehicle is accelerating or coasting. In addition, this noise may be present in two-wheel drive with the manual hubs in the LOCK position or with the automatic locking hubs engaged, but to a lesser degree. To improve this noise, rotate the tires per the frequency and method directed by the owner guide, adjust the individual tire pressure as specified on the safety compliance certification label and confirm that the front-to-rear axle ratio difference is not greater than 0.01.
NOTE: It is important that the rear axle noise on vehicles equipped with either a manual or automatic overdrive transmission be evaluated in both direct drive and overdrive.
Vibration, technically, is a high-frequency trembling, shaking or grounding condition, felt or heard, that is constant or variable in intensity and occurs during a portion of the total operating speed range. The types of vibrations that can be felt in the vehicle can be divided into three groups:
1. Vibrations of various unbalanced rotating parts of the vehicle.
2. Body and frame vibrations excited by powertrain, wind or road inputs.
3. Tip-in moans or resonance vibrations from stressed engine or exhaust system mounts or driveline flexing modes.
These vehicle vibrations can also be subdivided into those that occur at low speeds and those that are most noticeable at higher speeds. Since the dividing line between low and higher speed vibrations is not clear, there will be vibrations that overlap the two ranges.
Typical Low-Speed Vibrations (Less than 72 km/h [45 mph])
* Driveline vibrations due to driveline angles.
* Engine harshness.
* Power steering pump disturbances.
* Air conditioner compressor or drive belt vibrations.
* Take-off shudder (clutch or driveline problems).
* Brake roughness or harshness.
* Driveline roughness.
* Clutch torsion vibration.
* Manual transmission gear rattle.
* Exhaust vibration.
* Tire roughness due to high non-uniformity (force variation).
* Galled, dirty, rusty, worn or improperly lubricated driveline slip yoke splines or U-joint bearings.
Typical High-Speed Vibrations (Above 72 km/h [45 mph])
* Companion flange (end yoke) runout or imbalance.
* Driveshaft imbalance.
* Excessive tire-wheel and drum assembly imbalance.
* Rear axle pinion gear pitch line runout.
* Excessive tire and wheel runout.
* Worn suspension components.
* Front end accessory vibrations.
* Exhaust vibration.
Harshness is the term commonly used to describe the ride quality of the vehicle. Hard ride or harshness is usually caused by the tires or suspension system, namely:
* Over-inflated, wrong size or wrong type tire or wheel installed on the vehicle.
* Suspension not sufficiently lubricated.
* Worn suspension components.
* Suspension components installed with preload on pivot points, bearings and bushings.
* Units equipped with tires not specified by the manufacturer. (Different brand tires often give different ride qualities to vehicle.)
* Bent or bound-up shock absorbers.
* Heavy-duty components installed on vehicle.
* Improper installation of body or cab mounts (groundings).
Other vehicle ride motions may be summarized as follows:
* Vehicle bounce -- The vertical motion of a vehicle on its suspension system, front and rear in phase. A low frequency "float," an intermediate frequency "kick."
* Vehicle pitch -- The out-of-phase vertical motion of the front and rear of the vehicle. A flat ride would be considered the opposite of a pitch ride.
* Vehicle roll -- The side-to-side rotation of the vehicle body about the front and rear axles.
Verify the condition by road testing.
NOTE: For four-wheel drive vehicles, verify concern with known quality conventional tires. If symptom still exists:
1. Shift transfer case into two-wheel drive.
2. Unlock front hublocks (or remove front driveshaft).
3. If condition disappears, concern is in front axle or driveshaft.
4. If condition persists, remove rear driveshaft and road test using front drive.
5. If condition disappears, concern is in rear driveshaft.
6. If condition persists, see driveline chart or other sources.
Acceleration:
1. Light -- Increase in speed at less than half throttle.
2. Heavy -- half to full throttle increase in speed.
3. WOT -- Wide-open throttle.
Ambient Temperature: Surrounding or prevailing temperature. Normally, the temperature in the service area or outdoors, depending on where testing is taking place.
Articulation: Vertical movement of the front driving or rear axle relative to the frame of the vehicle to which they are attached.
Belt Chirp: An intermittent noise usually at idle caused by belt misalignment.
Belt Squeal: A continuous high-frequency noise caused by a frozen accessory or insufficient tension.
Boom: A very low-frequency (sometimes cycling) noise often accompanied by sensation of pressure on the eardrums.
Bound Up: Refers to a stressed, rubber-mounted component that transmits any NVH which would normally be absorbed by the mount. (See Neutralize.)
Brakes Applied: When vehicle is stationary, service brakes applied with enough force to hold vehicle against acceleration with transmission in gear or drive.
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 kingpin 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.
Coast/Neutral Coast: Engine/transmission taken out of gear with driveshaft/driveline by placing transmission selector in neutral or by depressing clutch (manual transmission).
Coupling Shaft: The front shaft in a two-piece driveline.
CPS: Cycle Per Second.
Cruise: Steady highway speed, neither accelerating nor decelerating; even pressure on accelerator pedal on level ground.
Controlled Rear Suspension Height: The height at which the components of a particular vehicle should be set when driveline angle measurements are made.
Deceleration: Slowing of vehicle by releasing foot from accelerator at cruise and allowing engine to slow vehicle without application of brakes.
Driveline Angle: Angle between the engine/transmission and the driveshaft or angle between the driveshaft and the rear axle pinion. Both are usually measured with a protractor.
Driveshaft (Propeller Shaft/Propshaft): Shaft which powers the rear axle input shaft (pinion shaft). Also, the rearmost shaft in a two-piece shaft.
Drivetrain: Includes all power transmitting components from the engine to the wheels, including clutch/torque converter, transmission, transfer case, driveline, and front or rear drive axles.
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 fails to fire at the proper time.
Engine Run-Up Test: Operation of engine through normal rpm range with vehicle sitting still, transmission in neutral. Used for engine and accessory vibration check.
Extension Housing Damper: A counterweight attached to an arm on the rear of the transmission extension housing and designed to "soak up" or dampen unwanted driveline or powertrain vibrations.
Flat Spots (Tires): Commonly caused by letting vehicle stand while tires cool off. Can be cured by again operating vehicle until tires are warm. Also, regular tire wear patterns in the tire tread resulting from wheel-locked skids.
Float: A cruising drive mode in which throttle setting matches engine speed to road speed, neither accelerating nor decelerating.
Gravely 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 over-inflated tires.
Hz: Hertz (Cycles Per Second).
Imbalance (or Unbalance): Out of balance; more weight on one side of a rotating component causing shake or vibration.
Inboard: Toward the centerline of the vehicle. (See Outboard.)
Isolate: Separate from the influence of other components.
NVH: Noise, Vibration, Harshness.
Neutral Engine Run-Up Test (NERU): Operation of engine through normal rpm range with vehicle standing still, transmission in neutral. Used for engine and accessory vibration check.
Neutralize (Normalize): To return to unstressed position. Used to describe various mounts and exhaust system hangers. (See Bound Up.)
Outboard: Toward the outside of the vehicle rather than toward the centerline. (See Inboard.)
Pinion Shaft (Stem): The input shaft to a driving axle, usually a part of the smaller driving or input gear of a "Ring and Pinion" gear set.
Pumping Feel: A 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, lateral is at 90 degrees to the plane of rotation.
Ring Gear: The large gear, driven by the pinion gear of a "Ring and Pinion" driving axle gear set. Not applicable to transaxle.
Road Test: Operation of vehicle under conditions designed to recreate the problem condition.
Runout: Out of round or wobble.
Shake: Low frequency vibration, usually results in visual movement of components.
Slip Yoke (Slip Spline): Driveshaft coupling device (half of a U-joint) which compensates for changes in shaft length due to articulation of axle; used at one end of driveshaft.
Tire Force Variation: Tire vibration 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.
Two-Plane Balance: Radial and lateral balance.
Tire Deflection: Bending of the body of the tire during rotation.
T.I.R.: Total Indicated Runout.
Tip-In Moan: A light moaning noise heard when the vehicle is lightly accelerated, usually between 40-104 km/h (25-65 mph).
Vibration: Regular movement of a component that results in a sound or feel of movement.
See also:
http://www.supermotors.net/registry/6098/56159-4 
![nvhworksheet.jpg Noise or Vibration, Four-Wheel Drive Vehicles
IF THE IMAGE IS TOO SMALL, click it.
Noise, defined as any unpleasant sound, may be described in a variety of ways such as tapping, chirping, squealing, whistling, buzzing, humming, clunking or booming. You can associate these various descriptions of noise with a probable cause. Based on experience, these descriptions will assist in isolating the problem and correcting it. Generally recognizable problem areas are engine, drivetrain, wind and road surface noises. Other less obvious areas that should be considered as noise problem sources are any of the problems that cause the vibrations described in this section.
Noise Acceptability
A gear driven unit, especially a drive axle, will produce a certain amount of noise. Some noise is acceptable and may be audible at certain speeds or under various driving conditions: for example, tire noise on a newly paved blacktop road. Such noise is in no way detrimental to the operation of the vehicle and must be considered normal.
Also, Traction-Lok or Limited-Slip axles may produce a slight chatter on slow turns after extended highway driving, which is normal.
Noise from the transfer case in four-wheel drive may be the result of transfer case chain noise. This noise may take the form of a high or low frequency whine or growl and is normal in four-wheel drive vehicles. The noise is most pronounced when driving on hard surfaced roads in four-wheel drive and is due to driveline binding between the front and rear axles causing the chain to contact the front or rear of the sprocket teeth depending on whether the vehicle is accelerating or coasting. In addition, this noise may be present in two-wheel drive with the manual hubs in the LOCK position or with the automatic locking hubs engaged, but to a lesser degree. To improve this noise, rotate the tires per the frequency and method directed by the owner guide, adjust the individual tire pressure as specified on the safety compliance certification label and confirm that the front-to-rear axle ratio difference is not greater than 0.01.
NOTE: It is important that the rear axle noise on vehicles equipped with either a manual or automatic overdrive transmission be evaluated in both direct drive and overdrive.
Vibration, technically, is a high-frequency trembling, shaking or grounding condition, felt or heard, that is constant or variable in intensity and occurs during a portion of the total operating speed range. The types of vibrations that can be felt in the vehicle can be divided into three groups:
1. Vibrations of various unbalanced rotating parts of the vehicle.
2. Body and frame vibrations excited by powertrain, wind or road inputs.
3. Tip-in moans or resonance vibrations from stressed engine or exhaust system mounts or driveline flexing modes.
These vehicle vibrations can also be subdivided into those that occur at low speeds and those that are most noticeable at higher speeds. Since the dividing line between low and higher speed vibrations is not clear, there will be vibrations that overlap the two ranges.
Typical Low-Speed Vibrations (Less than 72 km/h [45 mph])
* Driveline vibrations due to driveline angles.
* Engine harshness.
* Power steering pump disturbances.
* Air conditioner compressor or drive belt vibrations.
* Take-off shudder (clutch or driveline problems).
* Brake roughness or harshness.
* Driveline roughness.
* Clutch torsion vibration.
* Manual transmission gear rattle.
* Exhaust vibration.
* Tire roughness due to high non-uniformity (force variation).
* Galled, dirty, rusty, worn or improperly lubricated driveline slip yoke splines or U-joint bearings.
Typical High-Speed Vibrations (Above 72 km/h [45 mph])
* Companion flange (end yoke) runout or imbalance.
* Driveshaft imbalance.
* Excessive tire-wheel and drum assembly imbalance.
* Rear axle pinion gear pitch line runout.
* Excessive tire and wheel runout.
* Worn suspension components.
* Front end accessory vibrations.
* Exhaust vibration.
Harshness is the term commonly used to describe the ride quality of the vehicle. Hard ride or harshness is usually caused by the tires or suspension system, namely:
* Over-inflated, wrong size or wrong type tire or wheel installed on the vehicle.
* Suspension not sufficiently lubricated.
* Worn suspension components.
* Suspension components installed with preload on pivot points, bearings and bushings.
* Units equipped with tires not specified by the manufacturer. (Different brand tires often give different ride qualities to vehicle.)
* Bent or bound-up shock absorbers.
* Heavy-duty components installed on vehicle.
* Improper installation of body or cab mounts (groundings).
Other vehicle ride motions may be summarized as follows:
* Vehicle bounce -- The vertical motion of a vehicle on its suspension system, front and rear in phase. A low frequency "float," an intermediate frequency "kick."
* Vehicle pitch -- The out-of-phase vertical motion of the front and rear of the vehicle. A flat ride would be considered the opposite of a pitch ride.
* Vehicle roll -- The side-to-side rotation of the vehicle body about the front and rear axles.
Verify the condition by road testing.
NOTE: For four-wheel drive vehicles, verify concern with known quality conventional tires. If symptom still exists:
1. Shift transfer case into two-wheel drive.
2. Unlock front hublocks (or remove front driveshaft).
3. If condition disappears, concern is in front axle or driveshaft.
4. If condition persists, remove rear driveshaft and road test using front drive.
5. If condition disappears, concern is in rear driveshaft.
6. If condition persists, see driveline chart or other sources.
Acceleration:
1. Light -- Increase in speed at less than half throttle.
2. Heavy -- half to full throttle increase in speed.
3. WOT -- Wide-open throttle.
Ambient Temperature: Surrounding or prevailing temperature. Normally, the temperature in the service area or outdoors, depending on where testing is taking place.
Articulation: Vertical movement of the front driving or rear axle relative to the frame of the vehicle to which they are attached.
Belt Chirp: An intermittent noise usually at idle caused by belt misalignment.
Belt Squeal: A continuous high-frequency noise caused by a frozen accessory or insufficient tension.
Boom: A very low-frequency (sometimes cycling) noise often accompanied by sensation of pressure on the eardrums.
Bound Up: Refers to a stressed, rubber-mounted component that transmits any NVH which would normally be absorbed by the mount. (See Neutralize.)
Brakes Applied: When vehicle is stationary, service brakes applied with enough force to hold vehicle against acceleration with transmission in gear or drive.
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 kingpin 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.
Coast/Neutral Coast: Engine/transmission taken out of gear with driveshaft/driveline by placing transmission selector in neutral or by depressing clutch (manual transmission).
Coupling Shaft: The front shaft in a two-piece driveline.
CPS: Cycle Per Second.
Cruise: Steady highway speed, neither accelerating nor decelerating; even pressure on accelerator pedal on level ground.
Controlled Rear Suspension Height: The height at which the components of a particular vehicle should be set when driveline angle measurements are made.
Deceleration: Slowing of vehicle by releasing foot from accelerator at cruise and allowing engine to slow vehicle without application of brakes.
Driveline Angle: Angle between the engine/transmission and the driveshaft or angle between the driveshaft and the rear axle pinion. Both are usually measured with a protractor.
Driveshaft (Propeller Shaft/Propshaft): Shaft which powers the rear axle input shaft (pinion shaft). Also, the rearmost shaft in a two-piece shaft.
Drivetrain: Includes all power transmitting components from the engine to the wheels, including clutch/torque converter, transmission, transfer case, driveline, and front or rear drive axles.
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 fails to fire at the proper time.
Engine Run-Up Test: Operation of engine through normal rpm range with vehicle sitting still, transmission in neutral. Used for engine and accessory vibration check.
Extension Housing Damper: A counterweight attached to an arm on the rear of the transmission extension housing and designed to "soak up" or dampen unwanted driveline or powertrain vibrations.
Flat Spots (Tires): Commonly caused by letting vehicle stand while tires cool off. Can be cured by again operating vehicle until tires are warm. Also, regular tire wear patterns in the tire tread resulting from wheel-locked skids.
Float: A cruising drive mode in which throttle setting matches engine speed to road speed, neither accelerating nor decelerating.
Gravely 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 over-inflated tires.
Hz: Hertz (Cycles Per Second).
Imbalance (or Unbalance): Out of balance; more weight on one side of a rotating component causing shake or vibration.
Inboard: Toward the centerline of the vehicle. (See Outboard.)
Isolate: Separate from the influence of other components.
NVH: Noise, Vibration, Harshness.
Neutral Engine Run-Up Test (NERU): Operation of engine through normal rpm range with vehicle standing still, transmission in neutral. Used for engine and accessory vibration check.
Neutralize (Normalize): To return to unstressed position. Used to describe various mounts and exhaust system hangers. (See Bound Up.)
Outboard: Toward the outside of the vehicle rather than toward the centerline. (See Inboard.)
Pinion Shaft (Stem): The input shaft to a driving axle, usually a part of the smaller driving or input gear of a "Ring and Pinion" gear set.
Pumping Feel: A 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, lateral is at 90 degrees to the plane of rotation.
Ring Gear: The large gear, driven by the pinion gear of a "Ring and Pinion" driving axle gear set. Not applicable to transaxle.
Road Test: Operation of vehicle under conditions designed to recreate the problem condition.
Runout: Out of round or wobble.
Shake: Low frequency vibration, usually results in visual movement of components.
Slip Yoke (Slip Spline): Driveshaft coupling device (half of a U-joint) which compensates for changes in shaft length due to articulation of axle; used at one end of driveshaft.
Tire Force Variation: Tire vibration 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.
Two-Plane Balance: Radial and lateral balance.
Tire Deflection: Bending of the body of the tire during rotation.
T.I.R.: Total Indicated Runout.
Tip-In Moan: A light moaning noise heard when the vehicle is lightly accelerated, usually between 40-104 km/h (25-65 mph).
Vibration: Regular movement of a component that results in a sound or feel of movement.
See also:
http://www.supermotors.net/registry/6098/56159-4](https://www.supermotors.net/getfile/576902/fullsize/nvhworksheet.jpg)