The propeller shaft or driving shaft is the member which connects the transmission to the differential.
The main shaft or output shaft from the transmission and pinion shaft extending from the differential unit are connected to the universal joints and the propeller shaft. A sliding joint is also used between the propeller shaft and the universal joint near the gearbox.
The rotary motion of the transmission main shaft is carried out through the propeller shaft to the differential, causing the rear wheels to rotate.
The propeller shaft has to withstand the torsional stresses of the transmitting torque and yet it must be light and well balanced so that vibrations and whip will not occur at high speeds. For these reasons, it is made of a strong steel tube. Solid propeller shafts are also used.
The propeller shafts may be exposed to the atmosphere or protected by an outer tube. Some operations include bearings at or near the propeller shafts to support it. On some applications, the propeller shafts are in two sections, supported by a center bearing and coupled together by a universal joint.
It is to be noted that the transmission main shaft and the differential pinion shaft are not in one horizontal level. The rear axle housing with differential is attached to the frame by springs, therefore, the distance between the gearbox and the differential changes due to road irregularities.
This also changes the angle of the drive. In order that the propeller shaft must take the curve of these two changes, it is provided with one or more universal joints to permit variations in the angle of the drive. Also, it must be provided with a sliding joint that permits the effective length of the propeller shafts to change.
Where the engine and axles are separated from one another, as on four-wheel-drive and rear-wheel-drive vehicles, it’s the propeller shaft that serves to transmit the driving force generated by the engine to the axles. The longer the shaft, a lot of liable it’s to bend, and bending is additionally promoted once the rotation is applied inflicting vibrations and leading to a rise in noise. For this reason, the propeller shafts have been designed to suppress vibrations arising from a good range of causes.