Canceled Out Driveline Angles

Engineers design drivelines in order to compensate for the accelerations and decelerations in order to produce a smooth, constant flow of power, as listed below:
- The transmission drives the front yoke of the propeller shaft at a smooth and constant speed.
- The first U-joint causes the power to fluctuate twice for each revolution of the propeller shaft.
- The second U-joint, oriented 90 degrees from the first U-joint, causes the power to fluctuate opposite that of the first U-joint.
- As the first U-joint slows down, the second U-joint speeds up.
This design causes I U-joint to cancel out the effect of the other U-joint. The cancelled effects result in a smooth, constant power flow from the output yoke of the propeller shaft.
Second-order driveline vibrations occur when the cancellation becomes unequal between the front U-joint and the rear U-Joint.
The main objective of this section is to correct the conditions that interfere with the proper cancellation effect of the U-Joint. The most common condition, especially where the launch shudder is concerned, is incorrect drivel me working angles. Other factors may aggravate the condition.
Address the following factors before you attempt to measure or correct the drivel me working angles:
- Worn, failed, damaged or improperly installed U-Joint
- Worn, collapsed, or improper powertrain mounts
- Incorrect vehicle trim height adjustment for the front suspension which aggravates the launch shudder
- Incorrect trim height adjustment for the rear suspension
- Trim height inspection includes trim heights that are too low or too high. The following vehicles fit into this category:
- Vehicles equipped with aftermarket lift kits
- Vehicles constantly loaded with cargo
- Custom conversion vans

On rear drive vehicles, the pinion nose tilts upward as you lower there are trim height.
If a second-order driveline vibration exists after you correct these conditions, measure and correct the driveline angles.

If the complaint is present only with cargo in the vehicle, perform the measurements with the vehicle fully loaded. Once you correct a second-order driveline vibration with the vehicle loaded, the vibration may reappear with the vehicle unloaded. The reverse of this condition is also true. You may have to reach a compromise with the customer in this case.