What the inputs mean
- Output angle: the transmission tail shaft, or the transfer case output on a four-wheel-drive rear shaft, measured on the output yoke or a machined surface in line with it.
- Driveshaft angle: the tube itself. The card below also works it out from the height drop and horizontal distance between the joint centres.
- Pinion angle: the pinion yoke centreline at the axle.
All three must use the same sign: here, positive means the part slopes down toward the rear. Park on level ground at normal ride height. If the ground is not level, the working angles are still right, because the slope adds the same amount to every reading and the calculator only uses differences.
The formula
A U-joint's working angle is the difference between the two parts it connects:
front angle = |driveshaft − output| rear angle = |pinion − driveshaft|Worked example
Output 3°, driveshaft 6°, pinion 1.5°. The front joint works at 3.0°, the rear at 4.5°, a difference of 1.5°. Output and pinion are 1.5° out of parallel. Rotating the pinion to 3° makes both joints 3.0° and the difference zero. For the driveshaft angle itself, a 4-inch drop over 48 inches of horizontal distance is 4.8°.
Standard shaft: equal and small
A single U-joint speeds up and slows down twice per turn when it runs at an angle. On a shaft with one joint at each end, the second joint cancels the first when both angles are equal and the yokes are in phase. The widely published guideline is to keep the two working angles within about 1 degree of each other, and small. The usual way to get equal angles is to set the pinion parallel to the output.
Double-cardan (CV) shaft
A double-cardan joint cancels its own speed change, so it can take a large angle at the transfer case. The single joint at the axle has nothing to cancel it, so the usual aim is a rear angle close to zero: the pinion points straight up the driveshaft. In the calculator, that means a pinion angle close to the driveshaft angle.
This page does the geometry only. It does not know your shaft length, speed or parts, and it does not say that a vibration will go away: check with your driveshaft shop.
Questions
How do I measure driveshaft angles?
Use an angle finder on the output yoke, the driveshaft tube and the pinion yoke, from the same side, with the vehicle at ride height. Write down whether each slopes down or up toward the rear and enter up as negative.
What should my pinion angle be?
It depends on the shaft. On a standard two-joint shaft, the common aim is a pinion parallel to the output so the two joint angles are equal: output 3° and pinion 3° under a 6° shaft gives 3.0° at each joint. On a double-cardan shaft, the pinion points up the shaft, so the rear joint angle is close to zero.
How much difference between U-joint angles is acceptable?
The widely published guideline for a two-joint shaft is within about 1 degree. Output 3°, shaft 6° and pinion 1.5° gives 3.0° and 4.5°, a 1.5° difference, outside that guideline.
How do I work out the driveshaft angle without an angle finder?
Measure the height drop between the U-joint centres and the horizontal distance between them. The angle is the arctangent of drop divided by distance: 4 inches over 48 inches is 4.8°.