Vibration Conditions

Technically, vibration is a low-frequency trembling, shaking, or grounding condition, felt or heard, that is constant 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 may 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 a 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.
1. Typical Low-Speed Vibrations (Less Than 72 kph [45 mph]):
- Exhaust vibration.
- Engine harshness.
- Driveline vibration due to improper driveline angles.
- Power steering pump vibrations.
- Air conditioner compressor or drive belt vibrations.
- Take-off shudder (driveline problems).
- Brake roughness or harshness.
- Driveline roughness.
- Tire flat spots.
- Driveline slip-yoke or companion flange.
- Automatic transmission clutch slippage.
2. Typical High-Speed Vibrations (Above 72 kph [45 mph]):
- Axle and companion flange runout.
- Driveshaft imbalance.
- Excessive tire-wheel and hub 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.
- Worn suspension components.
- Front end accessory vibrations.
- Exhaust vibration. Exhaust vibration is greatly reduced in exhaust systems de-coupled by a flexible coupling and mounted with blade and block hangers.

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:
- Overinflated, wrong size, or wrong type tire installed on the vehicle.
- Suspension insufficiently lubricated.
- Worn suspension components.
- Suspension components installed with preload on pivot point, bearings, and bushings.
- Vehicles equipped with tires not specified by the manufacturer (different brand tires often give different ride qualities to the vehicle).
- Bent or bound-up shock absorbers.
- Heavy-duty components installed on vehicle.

Other harshness conditions that effect ride quality 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.