Differential

The differential is a gearbox located between the drive wheels that serves two critical functions: it redirects the rotational power from the driveshaft (or transmission output) by 90 degrees to the axle shafts, and it allows the left and right wheels to rotate at different speeds when the vehicle turns. Without a differential, the driven wheels would be forced to spin at the same rate, causing tire scrubbing, drivetrain stress, and poor handling through corners.

The most common type is the open differential, which uses a set of spider gears (also called planetary gears) to split torque equally between both wheels while permitting speed differences. While simple and reliable, open differentials have a weakness: if one wheel loses traction, all the power goes to the spinning wheel. This limitation led to the development of limited-slip differentials (LSD), which use clutch packs, viscous fluid, or gear mechanisms to transfer more torque to the wheel with grip.

Vehicles can have front differentials (front-wheel drive), rear differentials (rear-wheel drive), or both plus a center differential (all-wheel drive and four-wheel drive systems). Differential fluid — a heavy gear oil — lubricates the gears and bearings inside the housing. This fluid breaks down over time and should be changed according to the manufacturer's schedule, typically every 30,000 to 60,000 miles.

Symptoms of differential problems include whining or howling noises (especially at specific speeds), clunking when shifting from drive to reverse, vibration, and fluid leaks from the differential cover or pinion seal.