Buick Encore 2012-2019 Service Manual / General Information & Maintenance / Vibration Diagnosis and Correction / Vibration analysis - road testing (EL-38792-A ELECTRONIC VIBRATION ANALYZER)

**Test Description**

The numbers below refer to the step numbers on the diagnostic table.

5

Obtaining rotational speed for the components rotating at tire/wheel speed is critical to systematically eliminating specific vehicle component groups. These component rotational speeds can be generated by using the EL-38792-VS Vibrate Software , or through calculating them manually.

10

**NOTE:** *Be certain to OBSERVE for disturbances that match the
customer
description FIRST, then look at the EL-38792-A Electronic Vibration
Analyzer 2 (EVA 2) frequency which corresponds with that disturbance.*

Proper location of the EL-38792-A Electronic Vibration Analyzer 2 (EVA 2) , sensor onto the component which is most excited by the vibration disturbance is critical to obtaining an accurate frequency reading.

This test will duplicate virtually any disturbance which occurs while the vehicle is in motion.

11

Accelerate to a speed high enough above the speed of the disturbance to allow for the time needed to shift into NEUTRAL and for the engine to decrease in RPM to idle speed, before coasting down through the disturbance range.

12

This test will either eliminate or confirm the engine as a contributing cause of the customer concern.

**Vibration Analysis - Road Testing**

**VIBRATION ANALYSIS - ROAD TESTING (CH-51450-NVH OSCILLOSCOPE)**

**Special Tools**

- CH-51450-NVH Oscilloscope Diagnostic Kit (w/NVH)
- EL-47955 Multi Diagnostic Interface (MDI)

For equivalent regional tools, refer to Special Tools and Equipment.

**Test Description**

The numbers below refer to the step numbers on the diagnostic table.

**NOTE:** *Be certain to OBSERVE for disturbances that match the
customers description
FIRST, then look at the CH-51450-NVH Oscilloscope Diagnostic Kit (w/NVH)
frequency which corresponds with that disturbance.*

10

Proper location of the CH-51450-NVH oscilloscope accelerometer onto the component which is most excited by the vibration disturbance is critical to obtaining an accurate frequency reading.

This test will duplicate virtually any disturbance which occurs while the vehicle is in motion.

11

Accelerate to a speed high enough above the speed of the disturbance to allow for the time needed to shift into NEUTRAL and for the engine to decrease in RPM to idle speed before coasting down through the disturbance range.

12

This test will either eliminate or confirm the engine as a contributing cause of the customer concern.

**Vibration Analysis - Road Testing (CH-51450-NVH Oscilloscope)**

**COMPONENT ROTATIONAL SPEED CALCULATION**

**Special Tools**

- CH-51450-NVH Oscilloscope Diagnostic Kit (w/NVH)
- EL-38792-A Electronic Vibration Analyzer (EVA) 2
- EL-47955 Multi Diagnostic Interface (MDI)

For equivalent regional tools, refer to Special Tools and Equipment.

**NOTE:*** If using the CH-51450-NVH Oscilloscope Diagnostic Kit (w/NVH)
, the
component rotation is integrated into the tool. The diameter of the pulley will
need to be measured and manually entered into the NVH software.*

**Tire Rotational Speed**

**Determining Tire Revolutions Per Second at 8 km/h (5 mph) - Using EVA**

Tire and wheel assembly rotational speed can be obtained through using the EL-38792-A Electronic Vibration Analyzer (EVA) 2. Perform the following steps using the EL-38792-A Electronic Vibration Analyzer (EVA) 2 to obtain the rotational speed at 8 km/h (5 mph). Use the Enter key to advance and the Exit key to backup.

- On the Main Menu screen, select Auto Mode.
- On the Suspected Source screen, select Vehicle Speed.
- On the Tire Info Source screen, select Manual Entry.
- On the Tire Width screen, enter the specific width of the tires.

For example: For a P245/45/R18 tire, enter 245.

- On the Aspect Ratio screen, enter the specific aspect ratio of the tires.

For example: For a P245/45/R18 tire, enter 0.45.

- On the Rim Diameter screen, enter the specific rim diameter size.

For example: For a P245/45/R18 tire, enter 18.0.

- On the Driveshaft Configuration screen, enter FWD, even if the vehicle is a rear wheel drive.
- The next screen will display the tire size just entered for confirmation.

For example: 245 0.45 18.0 -Front Wheel Drive. If the tire size displayed is correct, press Enter.

- On the Vehicle Speed Units screen, press Enter, disregard mph or km/h.
- Press the Exit key several times slowly while watching the backwards progression of the screens. Stop at the Tire Info Source screen.
- On the Tire Info Source screen, select RPS at 5 mph.
- The next screen will display the revolutions per second (RPS) at 8 km/h (5 mph) for that specific tire size

For example: The P245/45/R18 will display 1.08 RPS.

**Calculating Tire Revolutions Per Second at 8 km/h (5 mph) - Without
Ocilloscope or EVA**

If the EL-38792-A Electronic Vibration Analyzer (EVA) 2 is not available, the tire and wheel assembly rotational speed can be calculated approximately by performing the following steps.

- Convert the rim diameter size from inches to centimeters.

For example: For a P245/45/R18 tire, the rim diameter of 18 in X 2.54 converts to 45.72 cm.

- Calculate the radius of the rim by dividing the rim diameter by 2.

For example: For a P245/45/R18 tire, the rim diameter of 18 is converted to 45.72 cm divided by 2 = rim radius 22.86 cm.

- Calculate the approximate tire sidewall height by multiplying the
specific tire tread width by the aspect
ratio, then reduce 7 percent from the amount by multiplying by 93 percent to
approximate load on the tire reducing the sidewall height.
For example: For a P245/45/R18 tire, tread width 245 mm X aspect ratio as a decimal 0.45 = 110 mm X 0.93 = approximate sidewall height 102.30 mm.

- Convert the calculated approximate tire sidewall height from millimeters to centimeters.

For example: For a P245/45/R18 tire, approximate sidewall height 102.30 mm converts to 10.23 cm.

- Calculate the approximate tire and wheel assembly radius by adding the rim radius and approximate sidewall height, both in cm.

For example: For a P245/45/R18 tire, rim radius 22.86 cm + 10.23 cm = approximate tire and wheel assembly radius 33.09 cm.

- Calculate the approximate circumference of the tire and wheel assembly
by multiplying 2 X pi, or
6.283185 X the approximate tire and wheel assembly radius.
For example: For a P245/45/R18 tire, 6.283185 X approximate tire and wheel assembly radius 33.09 cm = approximate tire and wheel assembly circumference 207.911 cm.

- Calculate the approximate revolutions per kilometer by dividing the
number of cm in 1 km, 100,000 cm
by the approximate tire and wheel assembly circumference.
For example: For a P245/45/R18 tire, 100,000 cm divided by approximate tire and wheel assembly circumference 207.911 cm = approximate revolutions per kilometer 480.975.

- Calculate the approximate revolutions per second (RPS), or Hz, by
dividing the approximate revolutions
per kilometer by the number of seconds to travel 1 km at a speed of 8 km per
hour, 450 seconds.
For example: For a P245/45/R18 tire, approximate revolutions per kilometer 480.975 divided by the number of seconds to travel 1 km at a speed of 8 km per hour, 450 seconds = approximate RPS, or Hz 1.069 rounded to 1.07.

**Calculating Tire Revolutions Per Second, or Hz at Concern Speed**

A size P235/75R15 tire rotates ONE complete revolution per second (RPS), or 1 Hz, at a vehicle speed of 8 km/h (5 mph). This means that at 16 km/h (10 mph), the same tire will make TWO complete revolutions in one second, 2 Hz, and so on.

- Determine the rotational speed of the tires in revolutions per second (RPS), or Hertz (Hz), at 8 km/h (5 mph), based on the size of the tires. Refer to the preceding Tire Rotational Speed information.

For example: According to the Tire Rotational Speed information, a P245/45R18 tire makes 1.08 revolutions per second (Hz) at a vehicle speed of 8 km/h (5 mph). This means that for every increment of 8 km/h (5 mph) in vehicle speed, the tire's rotation increases by 1.08 revolutions per second, or Hz.

- Determine the number of increments of 8 km/h (5 mph) that are present,
based on the vehicle speed in
km/h (mph) at which the disturbance occurs.
For example: Assume that a disturbance occurs at a vehicle speed of 96 km/h (60 mph). A speed of 96 km/h (60 mph) has 12 INCREMENTS of 8 km/h (5 mph): 96 km/h (60 mph) divided by 8 km/h (5 mph) = 12 increments

- Determine the rotational speed of the tires in revolutions per second,
or Hz, at the specific vehicle speed
in km/h (mph) at which the disturbance occurs.
For example: To determine the tire rotational speed at 96 km/h (60 mph), multiply the number of increments of 8 km/h (5 mph) by the revolutions per second, or Hz, for one increment:

12 increments X 1.08 Hz = 12.96 Hz, rounded to 13 Hz

**NOTE: **

- Compare the rotational speed of the tires at the specific vehicle speed
at which the disturbance occurs, to
the dominant frequency recorded on the EL-38792-A Electronic Vibration
Analyzer (EVA) 2 during
testing. If the frequencies match, then a first-order disturbance related to
the rotation of the tire/wheel
assemblies is present.
If the frequencies do not match, then the disturbance may be related to a higher order of tire/wheel assembly rotation.

- To compute higher order tire/wheel assembly rotation related disturbances, multiply the rotational speed of the tires at the specific vehicle speed at which the disturbance occurs, by the order number: 13 Hz X 2, for second order = 26 Hz second-order tire/wheel assembly rotation related 13 Hz X 3, for third order = 39 Hz third-order tire/wheel assembly rotation related If any of these computations match the frequency of the disturbance, a disturbance of that particular order, relating to the rotation of the tire/wheel assemblies and/or driveline components, also rotating at the same speed, is present.

**Component Rotational Speed Worksheet**

Utilize the following worksheet as an aid in calculating the first, second and third order of tire/wheel assembly rotational speed related disturbances that may be present in the vehicle.

If after completing the Tire/Wheel Rotation Worksheet, the frequencies calculated do NOT match the dominant frequency of the disturbance recorded during testing, either recheck the data, or attempt to rematch the figures allowing for 1 1/2 -8 km/h (1-5 mph) of speedometer error.

If the possible tire/wheel assembly rotational speed related frequencies still do not match the dominant frequency of the disturbance, the disturbance is most likely torque/load sensitive.

If after completing the Tire/Wheel Rotation Worksheet, one of the frequencies calculated DOES match the dominant frequency of the disturbance, the disturbance is related to the rotation of that component group - tire/wheel assembly related.

**Fig. 1: Tire/Wheel Rotation Worksheet**

**VIBRATION ANALYSIS - TIRE AND WHEEL**

**Test Description**

The numbers below refer to the step numbers in the diagnostic table:

4 A build-up of foreign material on a tire and wheel assembly and/or a damaged, abnormally or excessively worn tire and wheel assembly could cause a vibration disturbance.

6 Tire and wheel assemblies that exhibit excessive runout when measured while mounted on the vehicle, may or may not be contributing to, or causing a vibration disturbance. On-vehicle runout, if present, could contribute to, or cause a vibration disturbance, but the cause of the on-vehicle runout may not be the tire and wheel assemblies.

7 Tire and wheel assemblies that exhibit excessive runout when measured off of the vehicle could cause a vibration disturbance.

9 Tire and wheel assemblies that exhibit marginal runout-within acceptable limits, but close to the maximum-when measured off of the vehicle could still be contributing to a vibration disturbance, if its mating hub/axle flange also exhibits marginal runout. When the tire and wheel assembly and the hub axle flange are mounted to each other, the combined stack-up of their marginal amounts of runout could combine to produce an excessive amount of runout, which could cause a vibration disturbance.

14 Brake rotors and/or brake drums, if equipped, that exhibit excessive imbalance could contribute to, or possibly cause a vibration disturbance.

15 A hub/axle flange and/or wheel studs that exhibit excessive runout could cause a vibration disturbance.

16 When the tire and wheel assembly and the hub axle flange are mounted to each other, the combined stack-up of their marginal amounts of runout could combine to produce an excessive amount of runout, which could cause a vibration disturbance. Match-mounting or vectoring the tire and wheel assembly to the hub/axle flange will modify the amount of combined runout.

18 Force variation may be present in a tire and wheel assembly that exhibited acceptable balance and runout.

Force variation, if present, could contribute to, or cause a vibration disturbance.

20 Vibration disturbances could be affected by, or possibly caused by, components that are susceptible to steering input and/or torque-load input.

22 On-vehicle balancing, or finish-balancing can be used to reduce small amounts of imbalance which may be present as a result of the combined stack-up of the tire and wheel assembly with other components which may exhibit marginal balance.

**Vibration Analysis - Tire and Wheel**

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