Differential and Final Drive Questions and Answers

Answer: C

Oil thrown from the crown wheel is caught in a trough and led along a cast gallery to the pinion bearings. A pump is used only on heavy duty units. Blocking the gallery during a rebuild with sealant is a classic and expensive mistake. 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

Excess sealant squeezes into the housing and can break away to block a gallery or a bearing, so a thin continuous bead is what the manufacturer specifies. Some covers use a gasket instead. Thread sealant on bolts entering the oil space is a genuine additional requirement. 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

Tightening a little at a time in a diagonal sequence pulls the cover down evenly and avoids distorting the flange. The same principle applies to any flange clamped by several fasteners. Uneven tightening is the commonest cause of a leaking cover. 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

Listening on a steady throttle, on the overrun and on a trailing throttle at a range of speeds reveals whether the setting is correct. Temperature is a useful secondary check. A noise appearing on one condition only points directly to the flank at fault. 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 new surfaces bed in during the first few hundred kilometres and generate heat, so heavy loading and towing are avoided and an early oil change is often specified. Constant speed is actually undesirable, since varying the load spreads the bedding across the flank. 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

The fine metal released during bedding is best removed before it circulates, so an oil change at a few hundred kilometres is common practice. Backlash does not change measurably during bedding. Crown wheel bolts are torqued once and locked. 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

Crown wheel bolts are highly loaded and are secured with a thread locking compound or a tab washer, and many are specified as single use. Spring washers are inadequate at these torques. Wire locking is used in aviation rather than in automotive final drives. 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

Some designs use left hand threads so that the direction of rotation tends to tighten rather than loosen the bolts. Attempting to remove them the usual way shears the heads. Checking the thread direction before applying force is a lesson usually learned once. 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

Recording backlash, shim thicknesses, bearing preloads and component orientation before dismantling saves a great deal of time and often makes the difference between success and failure. Marking components is genuinely valuable and is standard practice, so the last option describes part of the same discipline. 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

Starting from the original shim pack and adjusting from there is far quicker than calculating from first principles, and it is the method every manual describes. The shims must be identified by location as well as by thickness. Recording them is a few moments well spent. 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.