Once the vibration can be readily duplicated and is thought to be abnormal, the next step is to identify the frequency of the vibration. (If the vibration has not yet been duplicated, refer to Road Test .) Use the Smart Electronic Vibration Analyzer (Smart EVA) in order to measure the vibration frequency. If the Smart EVA is NOT available, the vibration frequency can be categorized into different groups according to how the vibration feels or sounds. The majority of vibrations will fit into one of the following categories; depending upon whether the vibration can be felt or heard.

Refer to the following list of vibration category definitions:

Shake

A low frequency vibration, 5 to 20 Hz. Sometimes SHAKE is visible in the steering wheel, the seat, or the console. The best way to describe shake is to compare it to the way an out-of-round or imbalanced tire feels.

Customers may refer to shake using one of the following terms:

shake usually relates to one of the following two groups.

Roughness

A vibration with a slightly higher frequency than the shake, 20 to 50 Hz. Roughness is similar to the feeling of holding a jigsaw.

This type of vibration is usually related to driveline components.

Buzz

A vibration with a slightly higher frequency then roughness, 50 to 100 Hz. Buzz is similar to the feel of an electric razor. Buzz may be felt in the hands through the steering wheel, in the feet through the floor, or in the seat of the pants.

This type of vibration is often related one of the following:

Tingling

The highest frequency vibration that can still be felt. Tingling may sometimes produce a pins-and-needles sensation. Customers may say the vibration puts their hands or feet to-sleep.

Boom

A low frequency interior noise, 20 to 60 Hz. Sometimes the customer complains of a pressure in their ears. Examples of noises that are similar to boom include; a bowling ball rolling down an alley, deep thunder, or a bass drum.

Words commonly used to describe boom:

Boom may or may not be accompanied by a perceptible vibration (roughness).

Boom is usually related to driveline components.

Moan or Drone

A sustained tone at low frequency, 60 to 120 Hz, somewhat higher than boom.

Examples of noises that are similar to moan or drone include; a bumblebee, or blowing air across the top of a soda bottle.

Words commonly used to describe moan or drone:

Moan or drone may be accompanied by a perceptible buzzing vibration.

Many times moan or drone is related to one of the following:

Howl

A noise at mid-range frequency, 120 to 300 Hz. Howl sounds like the wind howling.

Whine

A prolonged, high-pitched sound; frequency, 300 to 500 Hz. Sounds that are similar to whine include; mosquitoes, turbine engines, and vacuum cleaners.

Whine is usually related to the meshing gears or gear noise.

At this point in the diagnosis, the vibration has gone through the following analysis:

Automotive vibrations are usually related to the rotating speed of a component. Calculate the speed of these components using either an engine speed method or a vehicle speed method. Use the engine RPM readings taken during the road test in order to diagnose the vibrations that are sensitive to engine speed.

Vehicle-Speed Related Calculation

If the vibration is vehicle-speed related, the rotational speed of the tires needs to be determined. As long as the vehicle is operated at a constant speed (km/h, mph), the tires will operate at their own constant speed. The speed of the tires can be measured in how many times the component (the tires) cycles or rotates in one second. This component rotational speed can then be compared to the frequency of the vibration, which is also measured in cycles per second.

For the calculation to determine the rotational speed of the tires, and for continued diagnosis of a vehicle-speed related vibration, refer to the following:

The Smart EVA program is designed to perform targeted frequency calculations on a suspected vibration source. The tire size, axle ratio, number of cylinders, vehicle speed and engine rpm are factored into a calculation that determines the predominant vibration frequency, amplitude and the suspected vehicle system producing the vibration.

1. Use the Smart EVA to determine the speed at which the vibration occurs.
2. From the Smart EVA main menu, select Auto Mode, then press enter; select Vehicle Speed, then press enter.
3. Enter the vehicle tire size information with one of three options:

•	RPS at 5 mph -- Refer to the Tire/Speed table below for the Hertz value at 8 km/h (5 mph) for that tire size.

•

Database -- Select the tire type and tire size from each selection screen. Tip: when browsing the tire size or axle ratio list, press a number key to go to a related point in the list; for example, press 1 to go to the top of the list; press 4 or 5 to go to the middle of the list; press 9 to go to the bottom of the list.

•	Manual Entry -- Select Manual Entry to enter tire size directly. Enter the tire width (100-500 mm), aspect ratio (0.30-1.50) and rim diameter (10.00-25.00 in).

4. Enter the driveshaft configuration.
5. Enter the axle ratio, refer to the Axle Ratio table below,(2.00-9.00) from the Axle Ratio selection screen. Note: Axle Ratio is not applicable if front wheel drive (FWD) is selected.
6. Select the vehicle speed units in miles-per-hour (MPH) or Kilometers-per-hour (KPH).
7. Enter the vehicle speed at which the vibration is felt.
8. As the test is run, the vehicle speed must be manually adjusted to match the actual vehicle speed:

•	Select the incremental step you want to increase/decrease vehicle speed, then press enter.

•	View the frequency ranges applicable for the speed selected, press enter to go to the active data screen or exit to go back one screen.

•	Press the up or the down key to adjust the on-screen vehicle speed on the live data screen to match the actual vehicle speed.

9. Data is displayed as averaged (A is displayed) or instantaneous (I is displayed). Press average (avg) key to toggle. The amplitudes of the vibrations detected are displayed in descending order beginning with line 2. Repair the strongest vibration first. One to three sources of vibration are identified:

•	TIRE 1,2,3 or 4 (1st, 2nd, 3rd or 4th order tire/wheel system concern).

•	PROP 1 or 2 (Propshaft concern).

•	OVERLAP (overlap of Tire 3 and Prop 1 frequencies).

•	UNKNOWN (vibration source is unknown).

10. Data is received through input A (A is displayed) or B (B is displayed). Press key 4 to toggle.
11. The vehicle speed (V) is displayed in mph or kph. Press the down or up key to manually adjust this figure to match actual vehicle speed.
12. An identification letter symbol displays during record (R) or playback (P).
13. During record or playback the event and frame numbers are displayed. If an event is not selected, a "?" appears. During record or playback the frame number cycles from 0 to 9; for example, 0:0, 0:1, 0:2-0:9.
14. Amplitude of the signal is displayed in number of G forces (G).

Steering and suspension assembly vibrations are the first level of testing for low-frequency vibrations that are sensitive to vehicle speed. The symptoms of a steering/suspension first-order vibration are a shimmy or a shake. This is usually felt in the steering wheel or in the seat. Inspect the following components for wear or damage: