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What is a Differential? Open, Locking and Limited Slip Explained

the automotive world, especially Off-road trucks and SUVs, the difference always comes out. Is the diff lock limited slip, open? Do you have a transfer case? 1st or 2nd gear? What is the final drive ratio? And that before turning to various brand loyalty, ” ford 9 inch,” or 12 volt chevrolet That’s what you kill. “

Conversation can be a bit confusing, especially for beginners. Here’s a quick rundown of what differentials are, the different types of differentials, and why differentials are important.

What is Differential?

Differentials serve one important purpose: to send power to two wheels or all four wheels of a vehicle while simultaneously turning the vehicle. When turning, the car changes direction at a certain angle according to the radius of the corner. To do that, each of the four wheels would need to rotate at slightly different radii. That is, each wheel moves at a different speed.

For non-drive wheels, this is fine. Nothing binds them. But there is only one engine, and he rotates only at one speed at all times. To allow two or more wheels to rotate at different speeds while receiving power from a single power source, each drive wheel is connected to a shaft with a gear at the end, which in turn is a gear in the differential. is connected to

A differential performs a basic vehicle function of allowing the vehicle to turn.


These gears join more gears in the center and are mounted at a 90 degree angle in the center and on the other side to the shaft of the other wheel. All in all, there are four gears in the center, one from each wheel shaft and two at her 90 degree angles. These four gears (usually bevel gears, by the way) are in the assembly.

Separately, another gear is attached to the assembly and another gear at the end of it connects to the drive shaft (which transmits power from the engine). A gear at the end of the drive shaft rotates a gear in the assembly, which in turn rotates the assembly, which in turn rotates the two wheels connected to the assembly.

When the vehicle travels in a straight line, all drive wheels rotate at the same speed as the assembly rotates. That is, he in the assembly does not need to rotate any of the four gears. But when the vehicle starts rolling, each drive wheel must turn at a different speed. To make up for the difference, four gears are actuated, with the gear on the faster moving wheel effectively rotating around the gear on the slower moving wheel, and the entire assembly rotating as the vehicle turns corners. will move. wonderful!

What is an open differential?

All of the above also describes an open differential. A spherical mass in the center of the axle houses six gears, connected so that each wheel rotates at the desired speed. This is a very standard set-up for a vehicle that isn’t really intended for off-roading.

This is the trouble with open differentials. If one drive wheel has less traction than the other, there is no way to stop it from spinning while the other is waiting. When the road surface becomes bumpy, the weight of the vehicle shifts. Alternatively, there may be patches of uneven spots such as mud or rocks, loose gravel, sand, or moss. That’s where limited slip differentials and locking differentials come in.

Lexus LX600

The Lexus LX 600 F sports handling uses a Torsen limited slip differential.


What is a Limited Slip Differential?

A limited slip differential is an open differential with additional parts that help both drive wheels turn at or near the same speed. The traditional mechanical method of achieving limited slip of the differential is to use an open differential design and install a viscous coupling. Rather than physically connecting two wheels, a viscous coupling “connects” them by attaching a pair of clutches to the end of each wheel and filling the space between them with a thick viscous fluid. .

Basically, when one wheel starts spinning at a different speed than the other, rather than just the gear in the housing, the two clutch plates start spinning next to each other, creating a thick viscous fluid in the process. The fluid is agitated. This additional resistance makes it harder for the two wheels to spin at different speeds, causing more torque to go to the wheels with more traction. Good thing!

Modern cars mimic this behavior by applying braking pressure to the spinning wheels, the ones with less traction. Commonly called a brake-based limit-slip differential, it’s really just an open differential with the help of software and a braking system.

In fact, there are multiple ways to limit differential slip. These are just some of the most common.

mercedes g class

The Mercedes G-Class is one of the most capable off-roaders on the planet, with front, rear and center locking differentials.


What is a locking differential?

A locking differential is a differential that mechanically locks the two wheels together, locking the engine so they all spin at virtually the same speed. And it does so whether you’re turning a corner, on two different surfaces, or whether one wheel is on the ground at all.

This differential is simple and effective in overcoming difficult terrain. Just know that when you tell your car to turn a corner something has to skid. But note that it can have a locking, rear, front or center differential. Each serves a slightly different purpose.

locking center differential

A locking center differential keeps the front and rear axles rotating at the same speed. Additionally, each wheel may be connected by an open or limited slip differential, which means that individual wheels can spin at different speeds.

Locking the rear differential

Locking rear differentials are the most common type because they allow both rear wheels to rotate at the same speed for traction, while the front wheels rotate at different speeds to maintain some steering ability. is.

front differential lock

A locking front differential is present to aid trucks and SUVs, especially in treacherous terrain. A front-lock differential is most often used in conjunction with a rear-lock differential rather than alone. They are used when you want all four wheels of a four-wheel drive vehicle to turn at the same speed and go straight through a slippery road surface. Turning ability with the front differential locked is quite limited.

2021 JeepĀ® Wrangler Rubicon 392

Many crossovers have all-wheel drive systems, but the Jeep Wrangler uses a two-speed transfer case to switch between two-wheel and four-wheel drive.


What is a Transfer Case?

Four wheel drive trucks often include another part called a transfer case. These power all four wheels, not just two. A two-speed transfer case has a similar function, but incorporates an additional gear set that acts as a torque multiplier, making the engine rev significantly higher to reach the same speed. This allows the vehicle to climb particularly steep and slippery surfaces.

What is Final Drive Ratio?

The gear that connects the engine to the wheels in the differential is called the final drive ratio. Changing this number will also change the rotational speed of the engine compared to the speed of the car. In general, the higher the final drive ratio, the greater the torque increase and the lower the top speed.

There it is. Differentials allow the vehicle to turn, but they can also completely change how power is distributed and applied to the pavement – gravel, dirt, sand, rocks, etc. What is a Differential? Open, Locking and Limited Slip Explained

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