What is a Differential and How Does it Work with Differential Diagram

What is a Differential and How Does it Work with Differential Diagram

View All Parts From This Machine: John Deere 724J Wheel Loader
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While you might already know that every time you round a corner in a wheeled machine a differential is being put to work, you might still wonder exactly how it works, what it does, and how all its parts come together to pull off its tasks. Whether you’re simply an inquisitive reader in search of knowledge or you have a differential disassembled in your shop, we’ve put together this simple overview of differentials — with images and videos — to help demystify differentials.

Inside the differential gears work in coordination to allow the differential to change the direction of power, send power to each wheel, and allow each wheel to operate independently. » Click video to play/pause animation.


What is a Differential?

At its most basic, a differential is a system of interconnected gears powered through a driveshaft that (most commonly) accomplishes four tasks:

The Differential Changes the Direction of Power

If you imagine the power being output from an engine traveling along driveshafts to the wheels, it will immediately be clear that for each powered wheel that energy will need to be converted 90 degrees. To do this, a differential uses a drive pinion connected perpendicularly to a ring gear. As the drive pinion rotates, the teeth in the drive pinion turn the ring gear and rotate the force 90 degrees so it can be applied to the wheels.

The Differential Divides Power Between Wheels on the Same Axle

In the case of front and rear differentials, two powered wheels exist at opposite ends of the differential. At the same time as the direction of power is rotated, the differential also splits the power and sends power to each of the wheels.

The Differential Alters Torque Through Gear Reduction

Because of the configuration of the differential, a differential can also be used to transfer power with a high rotational force into output with a lower speed, higher torque force.

The Differential Allows Wheels to Turn at Different Speeds Relative to Each Other

With the exception of a locked differential, one of the most important functions of the differential is undoubtedly its ability to allow each wheel to rotate at different speeds. If you’ve ever pushed a cart where wheels are directly fixed to each other in a solid axle, you already know that since the rotation of each wheel is locked, turning becomes more difficult. By connecting the axles (and in turn the wheels) in a way that allows for changes in the rotational speed of each, the difficulties of cornering are greatly reduced.

A diagram of a number of parts in the differential.
A pulled apart view of the differential gives a better look at how each part works inside the differential.

How Does a Differential Work to Allow Each Wheel to Turn Independently?

Every time a wheeled machine rounds a corner, the distance each wheel needs to travel is no longer equal. As the inside wheel carves a path along part of a smaller curve, the outside wheel must cover a longer path that can be amplified by the sharpness of the curve and the width of the axles. Without a differential this difference would force either the inside wheel to slip as it rotates too fast or the outside wheel to skid as it rotates too slow. Overtime, this constant imbalance would wear heavily on tires, axles, and the entire machine.

To correct this problem, the differential connects each axle through side gears and spider gears that allow a loose connection of the axles instead of a fixed connection. With each side gear mounted in a mirror fashion and connected to each other through spider gears mounted between them the side gears can either rotate in unison or, when a difference in force is detected, independently of one another.

As should be clear in the animation above, at times when one wheel is experiencing less resistance a look inside a differential would show the spider gears rotating to allow each wheel to turn at different speeds. 

What Are The Most Common Types of Differentials?

While the open (or standard) differential solves the issue of correcting for different rotational speeds of each wheel, the differential also introduces a new issue into the drive system: correcting for road conditions where the resistance of one wheel is greatly reduced through a loss of traction. To correct this a few modifications to the standard differential have been implemented.

Open (Or Standard) Differential

This type of differential is the one demonstrated in the above animation. In it, no system is implemented to correct for slippage when wheels encounter imperfect road conditions. However due to its reliability and the reduced complexity of its design compared to other differential types, it is the most common type of differential.

Locked Differential

A locked differential simply trades off the advantages of the wheels turning at different speeds for the advantages of the wheels always turning in unison by eliminating the independence of each axle. This effect can either be manually controlled and able to turn on and off or permanent. It is most common in vehicles where difficult road conditions (or even the non-existence of roads) is the standard and not the exception.

Limited Slip Differential

The limited slip differential is a marriage of the open differential and the locked differential wherein the differential routinely acts like an open differential but under certain conditions can be influenced to act like a locked differential. This effect can be created either through a viscous coupling or through a clutch system, and is most often found in high performance cars.

a rebuilt differential
Here, a freshly rebuilt differential sits at the center of a rear axle.

Where On a Machine is A Differential?

Depending on a machine and how power is divided and delivered to each of the wheels, a differential can exist at the front of the machine along the front axle, at the rear of the machine along the rear axle, or at the center of the machine dividing the front and rear axles.


Hopefully, how a differential works and what it does should be clear now, but if you’re interested in learning more, why not take a video trip into one of the Recon and Rebuild shops and see a differential being rebuilt? You can watch that in our How to Rebuild a Front and Rear Axle post. Or keep scrolling for a gallery of disassembled differentials and diagrams.

At H&R, we’ve earned a reputation as a top source for rebuilt transmissions for wheel loaders, articulated trucks, and other heavy construction equipment. We know that reputation comes from our commitment to our rebuild process and the expert knowledge our parts technicians bring to every project. If you’re in search of a replacement differential, reach out to our Parts Specialists and they’ll connect you to our deep inventory and provide fast information about availability and pricing.

Differential Image and Diagram Gallery

A differential hub.
A hub, bearings, gears, and carriers from a differential are waiting for a tech to put together for a differential rebuild.
A differential ring gear
The ring gear rests on its side. During a rebuild, a ring gear must be closely inspected to ensure teeth are not damaged and replaced if they are worn.
A differential spider shaft and spider gears.
The spider gears are set out, with the spider in the center, in anticipation for assembly and insertion into the differential.
A differential disassembled.
Here, an assembled differential with the back case removed gives a clear picture of the internals of the part.
A differential separated into its component parts.
The ring gear, side gears, and other parts are laid out on a workbench before being incorporated into the differential.
A tech works on a differential.
An H&R parts technician puts on some of the final touches before completing this differential rebuild.
Two axles at opposite ends of a differential in a diagram.
At each side of the differential, an axle connects the differential to a wheel and transfers power to the wheel.
Two bears in a differential diagram.
Bearings facilitate movement of axles and allow the internal of the differential to rotate freely.
A drive pinion at the center in a differential diagram.
A pinion shaft at the end of the center axle of the machine transfers power to the differential.
The ring gear in a differential in a differential diagram.
A large ring gear connects to the pinion drive and rotates the direction of force 90 degrees.
Two side gears in a differential diagram.
Side gears connected to shafts allow the turning of the ring gear to turn the wheels of the machine or — when the spider gears are put into motion — each wheel to rotate independently.
A set of spider gears in a differential diagram.
Spider gears are held together in a spider shaft, and while the shaft rotates in unison with the ring gear, the spider gears only turn when there is an imbalance in the rotational speed of each wheel.