Drive-line Geometry

How to measure and calculate drive-line angles

Place a spirit level protractor on the driveshaft about halfway between the transmission and the Differential. Read and record the angle shown on the protractor scale and note whether the driveshaft points up or down at the front. Record the angle as “3 degrees up” or “2 degrees down,”etc. Next, measure the transmission and differential angles. You must first locate a machined surface on the transmission and differential. The surface must be clean and true, free of any nicks and burrs. Again, record the angles and note whether the angles are up or down. Once all of the components have been measured, calculations can be made to figure the operating angles and to compare angles to see if the angle alignment is correct.

CALCULATE AND COMPARE OPERATING ANGLES

To calculate operating angles, you must add or subtract the component angles- that is, the relationship of the operating angles between the transmission, driveshaft and the differential, on each side of the driveshaft (drive and driven ends). This example shows 3 degrees of angle up for the transmission, 7 degrees up for the driveshaft and 3 degrees up for the differential. Please note that the transmission and the differential are parallel, the rules of geometry guarantee that the two operating angles will also be equal + or – 1 degree. Even though you know that the operating angles are equal + or – 1 degree, you must still calculate the operating angle (what the U-joint feels) to be sure that they are within specifications. Elbe U.S.A. specifies a maximum of 6 degrees of operating angle, with lower speed applications exceeding this limit. Because all of the angles are up, you need to subtract the smaller component angle from the larger component angle at each joint. The same would be true if all the component angles were down.