Drive Axles and Differentials

A drive shaft is connected to the output shaft of a rear wheel drive transmission to the rear differential. The rear differential can be a mono-beam type or independent rear suspension type. Mono-beam front or rear differentials are used for heavy load designs. Heavy duty trucks use mono-beam axle differentials. Four wheel drive vehicles use a transfer case attached to the transmission to transfer power to the front differential. The image below displays two rear mono-beam differentials and drive axles. They are both capable of delivering power to each wheel.

Below is an image of a solid axle. This design has limitation because the movement of one wheel affects the movement of the wheel on the opposite side.

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The image below has independent rear suspension because one wheel can move up and down independently of the other wheel.

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Independent rear suspension uses half shafts with constant velocity joints. Constant velocity joints allow more up and down travel. Constant velocity joints are also used on front wheel drive vehicles when it is necessary for the half shaft to turn when steering.

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Front wheel drive trans-axles use constant velocity joints on each side of a half shaft. The differential is incorporated in the transaxle. Each half shaft is connected to one of the front wheels.

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The driveshaft on a rear wheel drive vehicle uses constant velocity joint or U-joints. U joints are limited to the degree of drive angle. A rear wheel drive shaft can have no more than 3 degrees of drive shaft angle. The U joint angles must be within 1 degree of each other. When the degree angle is too great, constant velocity joints are used instead of U joints or double Cardon U joints are used.

Below is an image of a U joint at the rear of the driveshaft connected to a differential.

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Below is an image of a double cardon U joint used for steep drive shaft angles.

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How does drive shaft angle effect drive shaft rotation?

Drive Shaft Velocity You Tube

Driveline Servicing and Symptoms

The drive shaft bearing need some angle because the bearing need some rational force to allow the torque to contact the bearing surfaces. Because the CV joints or U joints are absorbing so much force they are subject to failure. Failing driveshafts have the following symptoms:

knocking or clicking noises coming from any wheel especially during turning or under a heavy load
vibrations upon acceleration
vibration at cruising speed or knocking at cruising speeds

Drive shaft failure is common. The CV joints are protected by dust boots. The boots retain grease packed into the bearings. If a boot fails the bearing becomes contaminated by water and dirt.

Below is an image of a damaged CV joint boot.

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Below is an image of a damaged CV joint. Metal can be seen in the boot.

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