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:

This design causes 1 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 driveline working angles (1,2). Other factors may aggravate the condition.

Address the following factors before you attempt to measure or correct the driveline working angles:

On rear drive vehicles, the pinion nose tilts upward as you lower the rear 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.

Second-Order driveline vibration has the following signs and symptoms:

Launch shudder is the most common complaint of a second-order driveline vibration.

Launch shudder occurs during acceleration from 0-40 km/h (0-25 mph). Launch shudder appears as a low frequency shake, wobble, or shudder. The driver may feel the vibrations in the seat or steering wheel at low speeds of 0-24 km/h (0-15 mph). The vibrations will increase in frequency as the vehicle speed increases. Launch shudder feels more like driveline roughness at higher speeds of 24-40 km/h (15-25 mph). At speeds greater than 40 km/h (25 mph) the vibration usually disappears.

Launch shudder vibration is equal to a second-order vibration of the driveline. The EVA will not perceive frequency information due to the transitory nature of launch shudder.

Tools Required

Driveline working angle does not refer to the angle of any 1 shaft, but to the angle that is formed by the intersection of 2 shafts.

The procedure for measuring and correcting driveline working angles depends on whether the vehicle is equipped with a propeller shaft consisting of 1 piece, 2 pieces, or 3 pieces.

In order to verify the accuracy of the adapter, inspect the angle of an accessible joint with the inclinometer prior to assigning the adapter on an inaccessible joint.

One-Piece Propeller Shaft System

Raise the vehicle on a suitable hoist or on safety stands. Ensure that the rear axle is supported at curb height and that the wheels are free to spin. Refer to Lifting and Jacking the Vehicle in General Information. Place the transmission in Neutral. Ensure that the vehicle has a full tank of fuel or the equivalent amount of weight in the rear to simulate a full tank. The weight of 3.8 liters of gasoline (1 gallon) is approximately 2.8 kg (6.2 lb).

Inspect the propeller shaft for correct phasing. Correct phasing means that the front and the rear U-joint are directly in line or parallel with each other so that proper cancellation takes place.

1. Rotate the propeller shaft so that the propeller shaft rear U-joint bearing cap is vertical.



2. Ensure that the front bearing cap is also vertical.
3. Place the inclinometer on the propeller shaft rear U-joint bearing cap in order to ensure that both U-joints are vertical.
4. Set the indicator line above the sight glass on 15 (the horizontal reference). Rotate the propeller shaft until the bubble centers in the sight glass. This action brings the rear U-joint to vertical.
5. Remove the inclinometer without disturbing the setting. Leave the setting on 15.
6. Install the inclinometer on the front U-joint. The bubble should remain centered plus or minus 3 degrees if the shaft is properly phased.

The out of phasing of the single-piece propeller shaft is very unusual. If the shaft is visibly out of place, the end yokes are welded on in the wrong position or the shaft is damaged due to twisting. In either case, replace the propeller shaft before continuing with this procedure.

The working angle of a U-joint is the difference between the angles formed when 2 shafts intersect. One piece propeller shaft systems have 2 working angles, the front (1) and the rear (2).

The angles of these components are most accurately measured from the U-joint bearing caps. Verify that the bearing caps are free of corrosion or foreign material in order to ensure accurate readings. Remove any snap rings that may interfere with the correct placement of the inclinometer. Reinstall the snap rings after you take the measurements.

Take the measurements from the same side of the propeller shaft in order to maintain consistent angle measurements (either on the driver side or on the passenger side).

Record the readings on a diagram like the one shown as you proceed through the measurements.

Evaluation

The 2 working angles in a one-piece propeller shaft system should be equal to within ½ of a degree for effective cancellation.

In order to change the working angles, shim the components up or down. Look closely at the existing angles. Use the existing angles and the shims in order to achieve the correct working angles.

Compared to horizontal or true level, the components located at the rear of the vehicle are usually lower than the components located at the front of the vehicle. This condition is called down in the rear. If a component with a down in the rear angle is shimmed up at the rear, the shim will bring the component closer to the horizontal (zero). Alternately, if a component with a down in the rear angle is shimmed down, the component will move farther from the horizontal (zero).

Rear axle wind-up may cause launch shudder even when all of the working angles are within specifications. Rear axle wind-up occurs when heavy torque during acceleration causes the pinion nose to point upward. In order to compensate for axle wind-up, tip the pinion nose downward. Install the axle shims incrementally, performing a road test after each shim. Add shims until the road test indicates that the shudder is eliminated.

Wedge shims of different sizes are available through the parts' system and independent suppliers for the purpose of shimming the rear axle angle. Wedge shims are available in 2, 3, and 4 degrees.

Caution: Never attempt to shim a rear axle using anything except shims that are designed for this purpose. Failure to do so will result in the shims falling out and a loss of vehicle control and that could cause personal injury.

Install the shims (5) in order to increase or decrease the angle of the rear axle pinion. Install the shims between the leaf spring (3) and the spring seat (2). Depending on the design of the suspension [leaf spring on top or underneath the axle (1)], and the direction of the desired change, install the shims with either the thick side toward the front of the vehicle or toward the rear of the vehicle.

Important: After installing the shims, ensure that the U-bolt has 2 or 3 threads above the nut. Ensure also that the center bolt, located in the spring seat, is long enough to seat in the locator hole. If these 2 conditions do not exist, use longer U-bolts and center bolts. Longer U-bolts and center bolts are available through local spring shops.

If a transmission requires shims, order the shims through the parts distribution system.

Installing most shims will change the transmission angle approximately ½ degree.

When shimming transmissions, use a shim made from steel stock at the necessary thickness. Ensure that the shim contacts the full width of the area to be shimmed. Do not use washers.