Vibration Conditions

Technically, vibration is a low-to high-frequency excitation, shaking or grounding condition, felt or heard, that is steady or variable in level and occurs during a portion of the total operating speed range. The types of vibrations that can be felt in the vehicle are divided into three groups:
- Vibrations of various unbalanced rotating parts of the vehicle.

NOTE: Halfshafts are not balanced and do not contribute to rotational vibration disturbances.

- Body and frame vibrations excited by powertrain, wind, or road inputs.
- Tip-in moans or resonance vibrations from stressed engine, 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 line between lower 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]):
- exhaust vibration
- engine harshness/vibration
- driveline vibration due to improper drivel me angles or bad U-joints
- power steering pump vibrations
- drive belt vibrations
- engine cooling fan vibration
- take-off shudder (driveline concerns)
- brake roughness or harshness
- driveline roughness
- excessive wheel runout
- tire flat spots
- driveline slip-yoke or pinion flange
- components/material trapped between the body and the frame, the engine and the frame or the engine and the body
- automatic transmission clutch slippage

Typical High-Speed Vibrations (Above 72 km/h [45 mph]):
- axle and pinion flange runout
- driveshaft imbalance
- excessive tire-wheel and brake disc or drum assembly imbalance
- tire roughness due to high non-uniformity (force variation) or out-of-balance condition
- rear axle pinion gear pitch line runout
- excessive tire and wheel runout
- components/material trapped between the body and the frame, the engine and the frame, or the engine and the body
- worn suspension components
- front end accessory vibrations
- exhaust vibration

Harshness is the term commonly used to describe the ride quality concern of the vehicle. A hard ride or harshness is usually caused by the tires or suspension system, namely:
- components/material trapped between the body and the frame
- overinflated, wrong size, or wrong type of tire installed on the vehicle
- suspension insufficiently lubricated
- worn suspension components
- suspension components installed with preload on the pivot point, the bearings, and the bushings
- vehicles equipped with tires that are not specified by the manufacturer (different brand tires often give different ride qualities to the vehicle)
- bent, bound-up or worn shock absorbers or shock isolators
- heavy-duty components installed on the vehicle
- air ride/load leveling suspension inoperative, damaged, deflated or improperly adjusted

Other harshness conditions that effect ride quality are 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 is considered the opposite of a pitch ride.
- Vehicle roll - the side-to-side rotation of the vehicle body about the front and the rear axles.