Differential and Final Drive Questions and Answers

Answer: A

Rapid heating expands the fluid until the plates are forced into contact, producing a sudden large increase in torque known as hump mode. It provides a useful reserve of traction but stresses the driveline. Repeated humping shortens the life of the unit. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: B

A locker engages a dog clutch that ties a sun gear to the cage, forcing both wheels to turn at the same speed regardless of grip. It must be disengaged on high grip surfaces. Automatic lockers engage and disengage without driver action. The order in which the effects act is what decides the outcome, so it is worth establishing first. Reading the definition literally, rather than recalling a summary, avoids the usual confusion.

Answer: C

With both wheels forced to the same speed, the different path lengths through a corner strain the axle until a tyre slips. On loose surfaces the tyres slip harmlessly. On tarmac the strain damages the driveline and scrubs the tyres. 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: D

Ratchet lockers drive both wheels until one overruns, at which point that side ratchets freely, so the unit locks under power and unlocks on a corner. The characteristic clicking and the abrupt handling are well known. Viscous and electronic units also act automatically by different means. 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.

Answer: A

The unit locks as soon as power is applied, forcing the vehicle to run wide, and the transition between locked and free is abrupt. Wandering at light throttle is also reported. The behaviour is accepted off road but is unpleasant on the highway. 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: B

Torque vectoring uses clutches or an overdriving gear set to send more torque to the outer wheel in a corner, generating a yaw moment that improves turn in. It goes beyond limiting slip to shaping the handling deliberately. The brake based approach achieves a cruder version. 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: C

Driving the outer wheel harder than the inner produces a moment about the vertical axis in the direction of the turn, which reduces understeer. The outer tyre does have to work harder, which makes the second option a genuine limit on how far the technique can be pushed. 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: D

A banjo housing is pressed from steel and welded, with a large aperture at the centre into which a separate differential carrier is bolted. The carrier can be removed without disturbing the axle. Salisbury housings integrate the carrier into the casting. 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.

Answer: A

Unbolting the carrier from the front of the housing allows the whole crown wheel, pinion and differential to be removed and worked on at the bench. A Salisbury housing must be worked on in place through a rear cover. Lightness and cost favour the banjo as well. 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.

Answer: B

In a semi floating axle a single bearing near the hub carries the weight, so the shaft is subjected to bending as well as torsion. A broken shaft allows the wheel to leave the vehicle. It is simple and adequate for cars and light vehicles. 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.