What is a differential, and why can ignoring potential diff problems become an expensive mistake?

What does your car’s differential actually do and how do you know if it’s breaking down? Discover the essential job of the differential and a few ways to spot its impending death.

The humble differential is one of those components that few people pay much heed to during regular maintenance of their cars. It’s tucked neatly out of sight, doing its job flawlessly… until it doesn’t.

Let’s start at the beginning though; what exactly is a differential? In simple terms, a differential uses specialised gears that allow two wheels, connected to the same axle, to turn at different speeds. When you turn a corner, the outside wheel needs to turn faster than the inside one, which is where the differential, or diff, comes in.


Diffs have become increasingly complicated over the years, evolving to meet the needs of more powerful and more refined cars. The three most common types of differential are the following:


The oldest and most common design, the open diff is simple, reliable and widely used. In the case of this diff, the powered pinion gear (at the end of the driveshaft) meshes with the ring gear, which in turn transmits power to both axles through a second set of gears. This setup is perfectly suited to most production cars. It’s only weakness is that when one wheel begins to slip, all power is essentially sent to the wheel with the least traction. Not ideal for clambering over rocks, or for high-speed racing.


A limited-slip diff is essentially an open diff with an integrated clutch system. The clutch mechanism will lock the left and right sides of the axle together when one wheel begins to lose traction. For obvious reasons, this is often the diff of choice for high performance vehicles, vehicles set up to tow heavy loads and drag racers.


A differential with torque vectoring represents the latest advancement in diff technology. Torque vectoring involves using a complicated array of sensors and electronics to gather data from the steering system, the throttle position, the road surface and more. The smart diff is then able to distribute power to each wheel, according to this data. In this way, it can provide maximum traction while corning, considerably increasing performance.

When you consider the importance of its function, it becomes immediately clear why it’s so important to ensure that your diff is in tip-top shape. It’s a relatively complicated component and any maintenance work on it is probably best left to the professionals. However, you can learn to identify diff problem warning signs, so that you can take action before real damage occurs.

If you encounter any of these symptoms, have your diff checked out as soon as possible:

  • A whining noise when accelerating.
  •  A whirring noise when decelerating.
  • Rumbling at the steering wheel or a whirring sound when you exceed a certain speed.
  • A regular clanking sound, which repeats every metre or so.
  • A banging sound when turning a corner.
  • Rumble while turning may indicate worn wheel bearings.
  • A steady vibration that increases with the vehicle’s speed can be caused by worn u-joints or an out of balance driveshaft.

Clunking only when starting to move or getting on and off the gas might be loose yokes, bad u-joints, a worn transfer case, or transmission parts.