Torsional Analysis Calculator

Enter driveline installation data into the fields, and the Spicer Torsional Analysis Calculator will perform an instant torsional and inertial analysis. You can then revise the data and correct problems right from your desk.

Prevent Torsional and Inertial Effects—Right from Your Desktop

U-joint operating angles are typically created during the design of a new vehicle, which is why vehicles usually do not leave the factory with vibration problems caused by improper u-joint operating angles. Yet over time, parts and suspensions wear, causing operating angles to change. In addition, businesses sometimes modify a vehicle’s wheelbase by shortening or lengthening it from the OEM’s original specification, inadvertently changing operating angles.

In the past, you would have had to go to your garage and add a few shims between the frame and axle. Then you would have to drive the vehicle to see if it vibrated. If it did, you would have to repeat the process over and over until you got the best results.

Yet with this calculator, you can prevent the torsional and inertial effects that can damage many of the driveline components in a vehicle, all online.

Getting Started

Gather the initial data

• Measure all angles with an accurate protractor (preferably digital)
• Measure all angles and determine all slopes from the driver’s side of the vehicle
• You will need to be able to accurately measure lengths, and to have a good understanding of slopes as they relate to drivelines

Slopes

• Down slope: When the rear of a component is lower than the front of a component
• Up slope: When the rear of a component is higher than the front of a component
• Example: Most axles have an end yoke that points up, but since the rear of the axle is lower than the front of the axle, it is a down slope for the purposes of this program

Determine the following:

• Maximum driveshaft RPM, determined by dividing driver RPM by the lowest transmission ratio
• The angle and slope of the driving member (usually a vehicle’s transmission)
• The true center line of the application
• The angle and slope of all driveshafts in the application
• The length, in inches, from the center of the u-joint to the center of the u-joint on all driveshafts in the application
• The angle and slope of the driven member (usually a vehicle’s axle)
• The offset, if applicable, of any components when looking down from the top

Identify the Problem

A driveline setup in a truck usually consists of a transmission attached to a driveshaft which attached to an axle. All three of these components usually have a down slope. Ideally, the angles and slopes between these components are not large enough to cause a torsional or inertial problem.

This calculator takes the data you have measured from your vehicle and determines if your torsional and inertial levels could cause a problem. It provides an alert if something is wrong.

If you get an alert, you can go back into the calculator and make modifications to the setup that you can then apply to the vehicle to remedy the problem. Typically, the corrective procedure involves changing the angle of the axle with a shim. This will then change the angle of the driveshaft, because the driveshaft is connected to the axle.

Re-enter your new data into the calculator. If further modifications are required, you will receive another alert and you can readjust the data and reanalyze the results, until you get the results you want. Your goal is to get torsional and inertial results that are as close to zero as possible.

How to Use the Torsional Analysis Calculator

This tutorial will walk you through the use of the calculator for a typical vehicle with two driveshafts. Use the figures below as though they are the data you measured from your vehicle. For this scenario, we have a vehicle with a new vibration problem: the shafts were removed, and the center bearing shims were inadvertently left out upon re-installation of the first shaft.

We will check the torsionals on the vehicle the way it is sitting, then go back and put the shims back in and check it again.

Note: Slope is immaterial when you enter a zero-degree angle.

Enter the initial vehicle data above

• If you notice a mistake in your data entries, you can return to that field and re-enter your data

• You can return to the Top/Side View buttons at any time to revise your entries if your results are too high
• When you go back, you can only change certain data, based on the type of vehicle data you have entered:
  • On a one-shaft vehicle, you can only change the angle of the driven member. You cannot change the angle of the driving member because it is “fixed” in the vehicle. You also cannot change the driveshaft because it is attached to the driven member and “moves” with any changes in the angle of the driven member.
  • On a multi-shaft vehicle, you cannot change the angle of the driving member or the rearmost driveshaft because it is attached to the driven member and “moves” with any changes in the angle of the driven member. However, you can change the angles of any driveshafts in front of the rearmost shaft. You usually do that by adding or removing shims under the center bearings.

Click “Results”

• Torsionals are high and the inertia effects at the driven end of the shaft are excessive
• That tells you that your angles are not canceled and your operating angle at the driven end of your shaft is probably too large

Add new data and re-calculate

• Click “Side View Angles and Lengths”

• Change the angle of the first shaft from zero to 3.5˚ degrees (the result of installing the center bearing shims); Select “Down”
• Note that the Shaft 2 Angle changed, because it is attached to Shaft 1
• Click “Results”
• Torsionals are now suitable and the inertia effects at the driven member have been reduced to acceptable limits

Points to Remember

• The smaller the operating angle, the smaller the inertia vibrations
• The closer the operating angles at each end of a driveshaft are to being equal, the smaller the torsional vibrations
• Our torsionals are so good because have small angles on both ends

Please download our step-by-step tutorial.