The differential - which houses an array of gears and bearings - is used to transform the twisting power of your driveshaft's torque into the spinning motion of your wheels. It gets its name from its ability to allow inner and outer wheels to turn at different speeds. (The outer wheel needs to turn faster than the inner wheel when you make a turn.)

If properly lubricated, a differential will offer many years of trouble-free operation.

Recommended Maintenance

• Replace every 24 months/48,000 km

Maintenance tips
Rear-wheel-drive or four-wheel-drive vehicles should have their differential lubes changed on a regular basis. (Consult your owner's manual for the specific schedule.)

Just keep in mind that all lubes are not created equal. Synthetic formulas will do a better job at lubricating parts in cold weather and handling extreme heat - as when turning. Positive-lock differentials - typically known by brand names such as "Positraction" or "Traction-Lock" - can require a special lubricant or the use of an additive.

Four-wheel-drive vehicles also have a separate differential for each axle.

Trouble-signs:

• A high-pitched sound when accelerating or slowing
• A howling sound
• A "clunking" when accelerating or shifting between reverse and drive
• Hopping when turning in one direction only

Hid you know?
Differentials are not completely sealed from the elements and water can find its way inside if the component is submerged. It's a common problem if you tow a boat or go off-roading in an SUV. If you're driving in these environments, replace the differential fluid on an annual basis.

Positive-lock differentials can shift torque from a slipping wheel to one that still has traction.