Propeller Shaft and Universal Joints Questions and Answers

Answer: A

The propeller shaft transmits torque from the gearbox output to the final drive pinion while accommodating the movement of the axle on its suspension. Half shafts carry the drive outward from the differential to the wheels, which is a separate stage. The shaft must also accommodate a change of length as the axle rises and falls. The order in which the effects act is what decides the outcome, so it is worth establishing first.

Answer: B

As the axle rises and falls the angle between the shaft and the gearbox changes and the straight line distance between the two alters, so both a universal joint and a sliding joint are required. Axle wind up under torque also changes the angle. A rigid connection would fail immediately. Checking which component actually carries the load settles most questions of this kind at once. Most errors here come from carrying across a result from a neighbouring case where it does not hold.

Answer: C

A cross and needle roller universal joint at each end allows the shaft to operate at an angle while transmitting the drive. The sliding spline accommodates the length change instead. Both features are needed on any shaft driving a live axle. Tracing the requirement back to the physical constraint that produces it makes the answer follow. Naming what changes and what stays the same is the reliable route through questions of this shape. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: D

The output speeds up and slows down twice per revolution when the joint operates at an angle, the variation growing rapidly with the angle. At thirty degrees the fluctuation is about fifteen per cent. Two joints in the correct phase relationship cancel the effect. The shared behaviour explains why these belong together and the differences explain why both exist. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb.

Answer: A

Placing a joint at each end with the yokes in the same plane and the two working angles equal makes the second joint undo exactly what the first did. Unequal angles leave a residual fluctuation that appears as vibration. Correct phasing is why the shaft must be reassembled in its original orientation. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision. A symptom that appears under one condition and not another is what narrows the diagnosis quickly.

Answer: B

Out of phase yokes leave the speed fluctuations of the two joints adding rather than cancelling, producing a torsional vibration felt through the vehicle. The shaft is marked so that the two halves can be reassembled correctly. It is a common error after a sliding joint is separated. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. The order in which the effects act is what decides the outcome, so it is worth establishing first.

Answer: C

A constant velocity joint keeps the driving and driven members in a plane that bisects the angle between the shafts, so no speed fluctuation occurs. Rzeppa and tripod designs are the common types. Front wheel drive would be impossible without them. Most errors here come from carrying across a result from a neighbouring case where it does not hold. Checking which component actually carries the load settles most questions of this kind at once. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: D

The Rzeppa joint uses six balls in a cage between an inner and outer race and accommodates the large angles that steering requires. The tripod inner joint permits the plunge that suspension movement demands. Each is used where its particular capability is needed. Naming what changes and what stays the same is the reliable route through questions of this shape. Tracing the requirement back to the physical constraint that produces it makes the answer follow. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: A

As the suspension moves, the distance between the differential and the hub changes, so the inner joint must allow the shaft to slide as well as to articulate. The tripod design does both. Angular capacity is greater at the outer joint because of the steering. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. The shared behaviour explains why these belong together and the differences explain why both exist.

Answer: B

Constant velocity joints use a special grease containing molybdenum disulphide, retained by the boot and packed in the correct quantity on assembly. Ordinary bearing grease is not adequate. Overfilling bursts the boot and underfilling starves the joint. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. The shared properties explain why these belong to one family, and the differences explain why more than one exists.