Spicer Driveline Installation Service Manual - Manual (Page 7)

4
Installation Techniques
Common Causes of
Vibration
Maximum Possible Driveshaft RPM
To calculate the maximum possible driveshaft RPM in vehicles having an overdrive transmission, divide the maximum possible
engine RPM by the overdrive ratio. (See examples below.)
Compare the maximum possible driveshaft RPM with the safe operating speed determined from the Safe Operating Speed Calcu-
lator. If the maximum possible driveshaft RPM meets or exceeds the safe operating speed determined from the calculator, you
must do whatever is required to raise the critical speed of the driveshaft you have chosen for the application.
Sample Specification:
To specify a driveshaft for the application described in Example 1 above, compare the safe operating speed for the driveshaft se-
lected with the maximum possible driveshaft RPM calculated (2658 RPM). Make sure the safe operating speed of the driveshaft
is greater than 2658 RPM.
Changing the Safe Operating Speed of a Driveshaft
A driveshaft’s safe operating speed can be raised by increasing its tube diameter or by shortening the installed center-to-center
length of the driveshaft. Changing the installed length of a driveshaft will require the use of multiple driveshafts with center bear-
ings.
Important: The critical speed of an assembly can be affected by driveshaft imbalance, improper universal joint operating angles,
or improperly phased driveshafts. (A properly phased driveshaft has the in-board yokes of the shaft in line with each other.) Each
of the above items will tend to lower the true critical speed from the values shown on the calculator.
Since critical speed can ultimately cause driveshaft failure, it is extremely important to be very precise in all applications.
Example 1:
Max. engine RPM: 2100
Overdrive ratio: .79
2100/.79 = 2658 maximum possible driveshaft RPM
Example 2:
Max. engine RPM 6000
Overdrive ratio: .66
6000/.66 - 9091 maximum possible driveshaft RPM