Measuring propshaft Angles

Measuring Propshaft Angles

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. The following diagnostics apply to front and rear propshafts.

Theory and Information

There are three commonly used powertrain angle configurations:

The first configuration is for rear propshafts of two-wheel drive or four-wheel drive trucks. Both working angles should be equal within specifications; however, as shown below, the front working angle (from the transmission to the propshaft) will be angled downward and the rear working angle (from the pinion gear to the propshaft) will be angled upward. This is because the engine and transmission, propshaft, and pinion gear are all tilted upward towards the front of the vehicle. This is an UP, UP, UP powertrain configuration..

The second configuration is for the front propshaft of a four wheel drive vehicle. Both working angles should be equal within specifications; however, as shown below, the front working angle (from the pinion gear to the propshaft) will be angled upward and the rear working angle (from the transfer case to the propshaft) will be angled upward. This is because the engine and transmission are tilted upward towards the front of the vehicle. If the front pinion gear was tilted upward to match the angle of the transmission, the working angles of the front propshaft would be excessive. Instead, the pinion angle is pointed downwards at the same angle the transfer case front output shaft (which is the same angle as the transfer case rear output shaft) is pointing up. This is an DOWN, UP, UP powertrain configuration..

The third configuration is for rear propshafts of two-wheel drive passenger cars. Both working angles should be equal within specifications; however, the front working angle (from the transmission to the propshaft) will be angled upward and the rear working angle (from the pinion gear to the propshaft) will be angled downward. This is because the engine and transmission are tilted upward towards the front of the vehicle and the pinion gear is is tilted downward towards the front of the vehicle. This is an UP, UP, DOWN powertrain configuration.

Improper propshaft working angles can cause a second order propshaft speed related vibration. The following procedures will allow you to measure and diagnose propshaft working angle problems. Before measuring propshaft angles, inspect the propshaft phasing and lateral alignment as shown below. Correct any phasing or lateral alignment problems first.

Propshaft Phasing

On multiple piece propshafts make sure the U-joints should all in phase with each other. (see the figure below). There are some exceptions to this rule which are designed to counter a vibration concern called "Launch Shudder". See the vehicle manufacturer's service information for more information.
Keep in mind that the front half of the propshaft shaft acts like an extension of the transmission/transfer case output shaft, and phasing is not as critical as single piece propshaft as long as this alignment is maintained.

Propshaft Lateral Alignment

On multiple piece propshafts make sure the propshafts are laterally aligned with each other. (see the photos below).
Lateral alignment can be checked by placing a piece of string stretched from the front U-joint bearing cap to the rear U-joint bearing cap. Visually inspect the alignment of the propshafts with the string. Relocate the center support bearing to make the propshaft assembly as straight as possible.

Improper Lateral Alignment

Relocate the center support bearing to make the propshaft assembly as straight as possible.

Center Support Bearing

Good Alignment

Tools Required

An inclinometer of some type must be used to measure transmission, propshaft, and axle angles. There are several different types of inclinometers including electronic versions. However, unless the inclinometer can attach to the U-joint bearing cap, it will probably not be able to measure the angle of the transmission or pinion pear. The tools shown below are used in the examples in this section.

Kent-Moore - http://gmspecialservicetools.spx.com/ J-23498-A Driveshaft Inclinometer, and J-23498-20 Inclinometer Adapter. The adapter is to be used when a cross-member or other components interfere with the placement of the inclinometer.

Setup Procedure

Lift and support the vehicle by the axles or tires, but not the frame. The full weight of the vehicle must be on the suspension to insure the propshaft is at the normal ride height.
Rotate the propshaft so that the transmission output shaft yoke 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 slip yoke U-joint bearing cap at a right angle with the propshaft. Keep the front of the inclinometer facing the rear of the vehicle.

Measurements

Measure the transmission angle:

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.

Rotate the inclinometer 90 degrees so that it is lined up parallel with the vehicle's propshaft.

Re-center the bubble with the swing arm and note the difference between where the swing arm was and where it is now.
- If the bubble moved towards the front of the vehicle, the transmission angle is upward.
- If the bubble moved towards the rear of the vehicle, the transmission angle is downward.
In the example below, the front of the vehicle is to the right of the photo and the bubble moved toward the front of the vehicle indicating an UPWARD angle. The sight glass bubble is centered when the swing arm is pointing to 19.25 degrees upward. The difference between 15 degrees and 19.25 degrees is 4.25 degrees. The angle of the transmission/transfer case being measured is UP 4.25 Degrees.

Measure the propshaft angle:

Install the inclinometer on the propshaft front U-joint bearing cap as shown below.
Set the swing arm on the center of the dial at 15 degrees. Rotate the propshaft to center the bubble on the sight glass as shown below. This establishes a horizontal reference point.
Rotate the inclinometer 90 degrees so that it is lined up parallel with the vehicle's propshaft.
Re-center the bubble with the swing arm and note the difference between where the swing arm was and where it is now.
- If the bubble moved towards the front of the vehicle, the propshaft angle is upward.
- If the bubble moved towards the rear of the vehicle, the propshaft angle is downward.
In the example below, the front of the vehicle is to the right of the photo and the bubble moved toward the front of the vehicle indicating an UPWARD angle. The sight glass bubble is centered when the swing arm is pointing to 23.5 degrees upward. The difference between 15 degrees and 23.5 degrees is 8.5 degrees. The angle of the propshaft being measured is UP 8.5 Degrees

Install the inclinometer on the propshaft rear U-joint bearing cap and obtain its angle. It should be the same as the front of the propshaft.

Measure the pinion gear angle:

Install the inclinometer on the rear axle pinion gear companion flange U-joint bearing cap as shown below.
Set the swing arm on the center of the dial at 15 degrees. Rotate the propshaft to center the bubble on the sight glass as shown below. This establishes a horizontal reference point.
Rotate the inclinometer 90 degrees so that it is lined up parallel with the vehicle's propshaft.
Re-center the bubble with the swing arm and note the difference between where the swing arm was and where it is now.
- If the bubble moved towards the front of the vehicle, the rear axle pinion angle is upward.
- If the bubble moved towards the rear of the vehicle, the rear axle pinion angle is downward.
In the example below, the front of the vehicle is to the right of the photo and the bubble moved toward the front of the vehicle indicating an UPWARD angle. The sight glass bubble is centered when the swing arm is pointing to 20.5 degrees upward. The difference between 15 degrees and 20.5 degrees is 5.5 degrees. The angle of the rear axle being measured is UP 5.5 degrees.

Calculating U-joint working angles:

After measuring the transmission, propshaft, and pinion angles, the working angles of the U-joints must be calculated.

The working angle is the difference between, or sum of the angles of the two components that the u-joint connects together.

Working Angle Calculation Guidelines

If both angles are upward, subtract the smaller angle from the larger angle to obtain the working angle.
If both angles are downward, subtract the smaller angle from the larger angle to obtain the working angle.
If one angle is upward and the other angle is downward, add the two angles together to obtain the working angle.

Example vehicle with bad working angles:

From the measurements shown in the above photographs,

The transmission angle was UP 4.25 degrees.
The propshaft angle was UP 8.5 degrees.
The pinion angle was UP 5.5 degrees.

Since the angles were UPWARDS, the calculated working angles will be the difference between the two angles.

The difference between the transmission angle and the propshaft angle is 8.5 - 4.25 = 4.25 degrees; the front working angle. (Could be out of specification depending on the propshaft rotational speed)
The difference between the propshaft angle and the pinion angle is 8.5 - 5.5 = 3.0 degrees; the rear working angle. (In specification)
The difference between the two working angles is 4.25 - 3.00 = 1.25 degrees. (Out of specification)

Example Vehicle with good working angles: 2003 GMC Sierra 2500 HD

Specifications

The two working angles should be equal within 1/2 of a degree on high speed propshafts and 1 degrees on low speed propshafts.
The working angles themselves should not exceed:
- 4 degrees on high speed propshafts (2700-3500 RPM). Propshaft speed = Engine RPM / Transmission gear ratio.
- 5 degrees on low speed propshafts (1800-2700 RPM). Propshaft speed = Engine RPM / Transmission gear ratio.
If the working angles cannot be brought into specification because of a suspension modification, an attempt to make both working angles the same should minimize the potential to create a vibration.
The working angles themselves should not equal zero. This is because with a zero working angle, the needle bearings within a U-joint will not rotate causing brinelling and premature wear of the U-joint.
On vehicles with two piece propshafts there is an odd joint. (see the figure below) The working angle of the odd joint should be kept below 1/2 degree and above zero degrees. This is because there is not a companion U-joint. Think of the front piece of a two piece propshaft as being an extension of the transmission output shaft.

On vehicles with three piece propshafts there are two odd joints. (see the figure below) The working angle of the odd joints should be kept below 1/2 degree and above zero degrees. This is because there is not a companion U-joint. Think of the front two pieces of a three piece propshaft as being extensions of the transmission output shaft.

Diagnostic Actions

If the working angles are out of specification, proceed with the following:

Ideally, the the rear working angle should be set to be 0.5 degrees less than the front working angle. This way as the pinion nose rises under acceleration or with the suspension under a load, the front and rear working angles will stay be within specifications.
When appropriate, add or subtract axle, transmission, engine, center support bearings, etc. shims to bring the propshaft angles within specifications and road test the vehicle again. Vibrate 5.1 has a "Propshaft Angle Correction Tool" found under the Tools menu, which will calculate the required shims and placement to bring the working angles into the ideal range.
When shimming transfer cases, transmissions, center support bearings, and axles, use a shim that is made from steel stock in the desired thickness. Make sure the shim contacts the full width of the area to be shimmed.

Correcting Propshaft Angle Problems

A rear wheel drive one-piece propshaft system has 8 different possible configurations and 32 possible corrections. A four wheel drive system has 32 different possible configurations and 128 possible corrections. Use the Propshaft Angle Correction Tool to assist you in deciding which corrections to make.

Select the component you wish to adjust from the following list:

This page was last modified Thursday, May 31, 2012 06:19:10 PM