Drive Shaft Parts

There are many parts in the drive train that transmit torque from the engine to the wheels. These include the clutch, transmission, drive shaft and the differential. The role of the drive shaft is to transmit torque while allowing for movement of the differential. The two main drive shaft parts are the slip yoke and the universal joint. The slip yoke allows the drive shaft to change its length, while the universal joints allow the shaft to change its angle relative to the transmission and differential. Other drive shaft parts include the rubber boot, flange yoke and the shaft itself.

The slip yoke is a splined tube with a yoke at one end. Depending on the type of transmission, the slip yoke may be mounted before or after the front universal joint. In the case of a slip yoke that joins at the transmission, the outer surface of the tube is polished and the inner surface is splined. The splined inner surface fits into the splines of the tail shaft, while the polished outer surface allows for movement through the tail shaft seal. The seal keeps oil from leaking out of the transmission, and also keeps dirt and water from entering it and causing damage. The slip yoke may also be covered with a flexible rubber boot for extra protection.

The drive shaft also needs to change its angle to allow for movement of the differential, which is fixed to the suspension and also moves up and down. The universal joints allow the drive shaft to turn while it is not inline with the transmission or differential shafts. Most drive shafts have a front and rear universal joint, but some also have a third joint that allow them to operate at a constant velocity. The most common type of universal joint used is the Cardan joint, which is also called a cross and roller joint. Its cross-shaped shaft and four roller bearings effectively create two hinges perpendicular to each other.

The largest and heaviest of all the drive shaft parts is the shaft itself. This is normally a steel tube but can also be made of aluminum or even composite materials. The shaft has a long length and a small diameter, and is hollow to reduce weight. There is no need to have a solid shaft because torque loads are mostly carried in the outer surfaces, so there would be little benefit to having all that extra weight. However, a hollow shaft is more likely to be bent if it strikes an object on the road. This causes massive vibrations that can easily damage or destroy the transmission and differential.

The last two drive shaft parts are the rear universal joint and flange yoke. These two parts are collectively called the rear joint and join the shaft to the differential. The flange yoke is fixed to the differential shaft, so it does not have a splined section like the slip yoke. It has a backplate which is bolted onto another plate connected to the differential shaft. To allow the front and rear joints to turn at the same speed, both yokes should have their ears aligned. The ears are the two metal stubs with holes that hold the universal joint bearings.

The most common cause of failure for drive shaft parts is insufficient lubrication. Noise coming from the drive shaft area usually indicates that one or more bearings needs to be cleaned and lubricated. It is important to regularly inspect the slip yoke and universal joints because they are exposed to dirt and water from the road surface. Unusual vibrations coming from the drive shaft area are usually caused by the shaft being out of balance. This can happen if the yoke ears are not aligned, or if the shaft is operating out of its normal range of movement.

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