Second Order Propshaft Speed Related Vibrations

Second Order Propshaft Speed Related Vibrations

Second order propshaft speed related vibrations cause two shakes or disturbances for each revolution of the propshaft. On standard 4-wheel drive or all-wheel drive vehicles, don't forget that the front propshaft can also cause this same type of vibration. Shift the vehicle in and out of four-wheel drive in an attempt to verify and isolate the concern.

Note: Some vehicles equipped with an automatic transfer case can still have the front propeller shaft rotate in two-wheel drive; however, it will not rotate at the same speed as it normally would in four-wheel drive. Shift the vehicle into four-wheel drive during diagnosis to eliminate the this potential diagnostic problem.

The following diagnostics apply to front and rear propshafts.

IMPORTANT: A component that is out of balance will NEVER cause a second or higher order vibration, only a first order vibration.

NOTICE: The following items should be checked in the order shown.

Second order propshaft vibrations are usually caused by:

Incorrect Vehicle Trim Height
Powertrain Mounting Problems
Failed or failing U-Joints
Improperly phased or twisted propshafts
Improper propshaft angles
Drive axle problems

Incorrect Vehicle Trim Height.

Vehicles that are heavily loaded, towing a trailer, or have modified suspension systems can cause the trim height to be incorrect resulting in improper propshaft angles. This will change the Universal Joint (U-joint, Cardan Joint, Hardy-Spicer Joint, Hooke's Joint) working angles which can cause improper U-joint acceleration and deceleration cancellation to take place. This can result in a second order propshaft speed related vibration. If the vehicle has been raised with a lift kit or lowered, the vibration may not be totally correctable. It is still possible to reduce the vibration to a minimum by following the procedures in this section.

Perform the following before measuring the trim heights:

Make sure the vehicle is on a level surface, such as a alignment rack.
Remove the alignment rack floating pins.
Set the tire pressures to the pressure shown on the certification label.
Check the fuel level. Add additional weight if necessary to simulate a full tank.
Make sure the rear compartment is empty except for the spare tire.
Close the doors and hood.
Inspect, measure and repair the front and rear trim height as necessary.

In the example shown above (2003 Chevrolet 2500 HD 4WD) the Z height should be 4.5 inches.

Worn, Collapsed, or Improper Powertrain Mounting

If the powertrain is allowed to move excessively, the working angles of the U-joints can be affected. This can cause improper U-joint acceleration and deceleration cancellation to take place. This can result in a second order propshaft speed related vibration.

Failed or failing U-Joints.

As the propshaft rotates, the Universal Joints (U-joint, Cardan Joint, Hardy-Spicer Joint, Hooke's Joint) actually speed up and slow down twice per revolution, this is not a constant velocity device. A U-joint which is failing can cause these speed fluctuations to be felt or heard by the driver of the vehicle. To diagnose U-joint problems, perform the following steps:

Mark the propshaft's relationship to the pinion flange and transmission/transfer case.
Remove the propshaft and Inspect the joints for looseness and roughness through their full range of motion.
Look for missing or damaged parts.

Improperly phased or twisted propshafts.

A twisted or improperly manufactured propshaft can have U-joints which are out of phase. This causes improper U-joint acceleration and deceleration cancellation to take place. The result is a second order propshaft speed related vibration. To check U-joint phasing, perform the following steps:

Rotate the propshaft so that the propeller shaft rear U-joint bearing cap is vertical.
Remove any dirt, or rust that might be present on the bearing cap. Remove any snap rings that may interfere with the correct placement of the inclinometer, but be sure to reinstall them.
Install an inclinometer on the rear propshaft U-joint bearing cap at a right angle with the propshaft. Keep the front of the inclinometer facing the front of the vehicle.
Set the swing arm on the center of the dial at 15 degrees as shown below.

Rotate the propshaft to center the bubble on the sight glass as shown below. This establishes a horizontal reference point.

Carefully move the inclinometer to the front U-joint bearing cap. Keep the front of the inclinometer facing the front of the vehicle.
Without moving the propshaft, re-center the bubble by moving the swing arm.
The difference between the rear and front readings is the propshaft phasing measurement. The bubble should remain centered in the sight glass within plus or minus three degrees if the propshaft is properly phased. Obviously, the lower the phase angle, the better the propshaft build.

General Specification: The difference between the two readings should be no more than 3 degrees.

If the phasing reading is within specification, go to the next step to measure propshaft working angles.
If the phasing is out of specification, replace the propshaft or have the propshaft repaired by a reputable driveline shop.
Road test the vehicle to insure the vibration concern has been corrected.

Improper propshaft working angles.

Click here to diagnose and repair improper propshaft working angles.

Drive axle problems.

Click here to diagnose and repair drive axle problems.

This page was last modified Thursday, March 05, 2009 09:02:31 PM