Differential and Final Drive Questions and Answers

Answer: A

The pair is run together with an abrasive compound after hardening, which corrects the heat treatment distortion and gives the matched contact pattern. That is why they must be replaced together. Ground sets are used where the highest accuracy is needed. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision. The shared behaviour explains why these belong together and the differences explain why both exist.

Answer: B

The lapped surfaces are matched to one another, so an unmatched pair has an incorrect contact pattern that no adjustment can fully correct. Noise and rapid wear follow. This is why the matched numbers stamped on the components must be checked. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: C

Examining the flanks for pitting, spalling, scuffing and the position of the wear pattern reveals both the condition and the history of the setting. Backlash is measured as well but tells less. The pattern is photographed before dismantling on a serious investigation. Most errors here come from carrying across a result from a neighbouring case where it does not hold. Reading the definition literally, rather than recalling a summary, avoids the usual confusion.

Answer: D

Repeated contact stress initiates subsurface cracks that break out as small pits, which then grow and coalesce into spalling. It is the classic fatigue failure of a gear flank. Scuffing is a lubrication failure with a quite different appearance. Naming what changes and what stays the same is the reliable route through questions of this shape. Most errors here come from carrying across a result from a neighbouring case where it does not hold.

Answer: A

When the film cannot separate the surfaces they weld locally and tear, producing the radial scratches characteristic of scuffing. Extreme pressure additives exist to prevent it. High temperature and heavy load are the promoting conditions. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. Naming what changes and what stays the same is the reliable route through questions of this shape.

Answer: B

Pitch line velocity is the product of the pitch circle radius and the angular velocity, and it governs the lubrication regime and the noise generated. High values demand better finish and more careful lubrication. It is a standard design parameter for any gear pair. Checking which component actually carries the load settles most questions of this kind at once. The order in which the effects act is what decides the outcome, so it is worth establishing first.

Answer: C

The contact pressure elastically flattens the surfaces and raises the viscosity of the oil enormously, forming a very thin but effective film. Boundary lubrication takes over where the film fails, which is where extreme pressure additives act. Understanding the regime explains why oil specification matters so much. Tracing the requirement back to the physical constraint that produces it makes the answer follow. Checking which component actually carries the load settles most questions of this kind at once.

Answer: D

Elastohydrodynamic film thickness depends on how strongly the viscosity rises with pressure, which is why synthetic oils with a high coefficient give thicker films. Pour point and flash point describe low and high temperature limits. Base number belongs to engine oils. The shared behaviour explains why these belong together and the differences explain why both exist. Tracing the requirement back to the physical constraint that produces it makes the answer follow.

Answer: A

Synthetic base stocks flow at lower temperatures and retain viscosity at high ones, and their pressure viscosity behaviour gives thicker films. Cost is higher rather than lower. A low pour point is desirable, so the last option inverts the requirement. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision. The shared behaviour explains why these belong together and the differences explain why both exist.

Answer: B

The pinion head bearing sits above the oil level and relies on splash from the crown wheel, so a low level starves it first. Baffles and oil galleries are provided to direct the flow. The crown wheel itself runs in the oil and is well supplied. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.