XL-7 2WD V6-3.6L (2007)
8 km/h (5 mph): 96 km/h (60 mph) divided by 8 km/h (5 mph) = 12 increments
3. Determine the rotational speed of the tires in revolutions per second, or Hz, at the specific vehicle speed 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 0.90 Hz = 10.80 Hz, rounded to 11 Hz
NOTE:
If the J 38792-A is not available, compare the calculated rotational speed to the frequency range associated with the symptoms of the vibration
concern.
4. Compare the rotational speed of the tires at the specific vehicle speed at which the disturbance occurs, to the dominant frequency recorded on the J
38792-A 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.
5. 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:
11 Hz X 2, for second order = 22 Hz second-order tire/wheel assembly rotation related
11 Hz X 3, for third order = 33 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.
Calculating Propeller Shaft Revolutions Per Second, or Hz at Concern Speed
1. Determine the first order rotational speed of the propeller shaft system in revolutions per second, or Hz, based on the first-order rotational speed of
the tire/wheel assemblies and the drive axle, or axles final drive ratio or ratios. 11 Hz X 3.42 drive axle final drive ratio = 37.62 Hz, rounded to 38
Hz, first-order propeller shaft rotation related
2. Compare the rotational speed of the propeller shafts at the specific vehicle speed at which the disturbance occurs, to the dominant frequency
recorded on the J 38792-A during testing. If the frequencies match, then a first-order disturbance related to the rotation of the propeller shaft is
present.
If the frequencies do not match, then the disturbance may be related to the second-order of propeller shaft rotation.
3. To compute a second order propeller shaft rotation related disturbance, multiply the first order rotational speed of the propeller shaft at the specific
vehicle speed at which the disturbance occurs, by the order number of 2: 38 Hz X 2, for second order = 76 Hz second-order propeller shaft
rotation related
If the computation matches the frequency of the disturbance, a disturbance relating to the second-order rotation of the propeller shaft 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 and the first and
second order of propeller shaft 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 11/2-8 km/h (1-5 mph) of speedometer error.
If the possible tire/wheel assembly and/or propeller shaft 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 or propeller shaft related.
