Propeller Shaft and Universal Joints Questions and Answers

Answer: C

Grease escapes and water and grit enter, and the joint wears rapidly until it clicks on lock and eventually fails. Replacing the boot promptly is far cheaper than replacing the joint. Boot condition is a standard inspection item. The order in which the effects act is what decides the outcome, so it is worth establishing first. Most errors here come from carrying across a result from a neighbouring case where it does not hold.

Answer: D

The characteristic rhythmic click on full lock under load is produced by the worn balls riding over the damaged tracks. A rumble in a straight line suggests a wheel bearing. The condition under which the noise appears identifies the component. Checking which component actually carries the load settles most questions of this kind at once. Naming what changes and what stays the same is the reliable route through questions of this shape. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: A

A worn tripod joint produces a shudder felt through the vehicle as it accelerates hard from low speed, particularly on full lock. The outer joint clicks instead. The two faults are distinguished by the symptom rather than by inspection. Tracing the requirement back to the physical constraint that produces it makes the answer follow. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: B

A hollow tube gives the greatest torsional stiffness for a given weight, since the material furthest from the axis carries the most stress. Aluminium and composite shafts are used where weight or critical speed matter. Solid bar would be needlessly heavy. The shared behaviour explains why these belong together and the differences explain why both exist. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: C

Torsional stiffness depends on the fourth power of the radius, so material near the axis contributes almost nothing and is better removed. The same principle governs bending. A hollow section also has a higher critical speed for its weight. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision. The order in which the effects act is what decides the outcome, so it is worth establishing first.

Answer: D

A shaft has a natural frequency of lateral vibration, and above the corresponding rotational speed it bows outward violently. The critical speed falls as the square of the length. Torsional strength is essentially unaffected by length. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. Checking which component actually carries the load settles most questions of this kind at once.

Answer: A

Halving the unsupported length quadruples the critical speed, which is why long shafts are made in two pieces with an intermediate support. Increasing the diameter helps as well. Adding wall thickness increases mass and stiffness together and helps very little. Most errors here come from carrying across a result from a neighbouring case where it does not hold. Tracing the requirement back to the physical constraint that produces it makes the answer follow. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: B

A sealed ball bearing in a rubber carrier bolted to the underbody supports the shaft while isolating vibration and permitting small movements. Perished rubber is a common source of vibration and noise. The bearing itself is sealed for life. Naming what changes and what stays the same is the reliable route through questions of this shape. The shared behaviour explains why these belong together and the differences explain why both exist. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Answer: C

A worn bearing or a perished rubber carrier allows the shaft to move and produces vibration that peaks at the speeds corresponding to the shaft resonances. Inspection with the vehicle raised usually reveals excessive play. Replacement is straightforward. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: D

The shaft is spun on a balancing machine and small weights are welded to correct the imbalance in two planes. Static balancing corrects only one plane and is insufficient for a long rotating component. The balance weights must not be disturbed during service. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Most errors here come from carrying across a result from a neighbouring case where it does not hold. Checking the units of each quantity catches a wrong formula before the arithmetic begins.