The propeller shaft, sometimes known as Cardon shaft or drive shaft is the medium by which the power from the engine driven gearbox is transmitted to the driving axles. It is made of steel and whether fitted in a front or rear wheel drive or between the main gearbox and an auxiliary gearbox, conforms to a similar pattern in which, one or two universal joints are incorporated. There are two types known as the open type and the enclosed type.
Whenever driving or braking efforts are applied through the rear live axle of a vehicle, the axle structure as a whole tends to turn over or rotate about the axis of the wheels. When the brakes are applied, the tendency to rotate in a forward direction, while when the vehicle is driven forward the axle structure tends to rotate backwards. The rotation of the axle structure must be prevented by a torque stay or by means of road springs, the later arrangement being known as hotch-kiss drive. The rear axle road springs are pivoted at front end and shackled at rear end, which resists the driving and braking torque.
The Open Type Propeller Shaft
This type is generally used on all heavy commercial vehicles and on most types of cars and light vehicles. The shaft is tubular in cross section and not enclosed in any outer casing or tube. It is fitted with a universal joint at each end, one to the gearbox main shaft through flange and the other to the driving axle bevel pinion shaft. On vehicles where the propeller shaft is comparatively long the shaft is made up of two portions connected by an additional universal joint and supported to the chassis cross member by a bearing. This centre bearing or support functions as a steady to obviate ‘Whip’ which may develop in the shaft. The front universal joint is splined to the propeller shaft and provides a telescope action for any fore and aft movement of the rear axle relative to the gearbox. When reassembling, the yokes of both universal joints must be in line and the correct position is usually indicated by arrows on the universal joints sleeve and on the propeller shaft.
The Enclosed Type Propeller Shaft
This type is of the solid cross-section and is more often enclosed in a tubular structure known as the ‘Torque Tube’ which is rigidly connected at its rear end to the rear axle casing and front end connected to the gearbox casing by a ball joint. As this tube resists the torque and twisting motion of the rear axle casing (due to application of brakes) and reaction of the drive, named as torque tube.
The propeller shaft is smaller in diameter than the open type and is supported by roller bearings inside the torque tube at the front and rear. There is only one universal joint fitted and this is located at the front end adjacent to the gearbox. The rear end of the shaft is attached to the bevel pinion shaft by a splined sleeve, which is secured by rivets to both the shafts to prevent longitudinal movement.
The front end of the torque tube is flared and is located between an inner cap and an outer cap both of which are semi-spherical in shape. The two caps, which form the housing for the torque tube is thus flexible mounted to allow for the up and down movement of the tube.
Where enclosed type of propeller shaft is fitted, the rear suspension is a transverse semi-elliptic spring which is mounted on the rear cross member of the chassis frame. The rear spring is shackled at both ends, so as to permit the axle to move in an arc when it rises and falls.
To reinforce the torque tube and axle casing two radius rods are fitted, the front ends of which are secured to the torque tube and the rear to the outer ends of the axle casing. Sometimes each rod is extended rearwards, beyond the casing to form the mounting for the rear spring shackles.
Removal of Propeller Shaft
(a) Unscrew bolts fastening rear propeller shaft coupling with the rear axle tail pinion coupling with the rear axle tail pinion. Carefully lower rear end of the propeller shaft on the ground.
(b) Disconnect fastening bolts of the rear propeller shaft from the front coupling carefully and remove the rear propeller shaft. Do not remove the sliding yoke from the propeller shaft.
(c) Remove bolts holding centre-bearing bracket of the front propeller shaft from the chassis cross member. Carefully lower the propeller shaft on the ground.
(d) Remove the coupling bolts of the front propeller shaft from the transmission end and remove front propeller shaft.
Refitting of Propeller Shaft
(a) Clean the mating surface of the coupling flanges on the tail pinion and on the centre-bearing bracket on chassis cross member.
(b) Connect the front coupling flange of the front propeller shaft to the transmission-coupling flange.
(c) Suspend the centre-bearing bracket on the chassis cross member through its bolts.
(d) Connect the front coupling flange of the rear propeller shaft to the centre bearing bracket rear flange on the chassis cross member through its bolts.
(e) Connect the rear-coupling flange of the rear propeller shaft to the tail pinion-coupling flange through its bolts.
(f) Grease all the nipples of the propeller shafts and universal joints and road test the vehicle.