Every modern vehicle has a differential, some even two (and if you’re reading this, you probably drive a vehicle with two!). Upgrading your differential is a smart move for the causal to serious off-roader. If you’re thinking about beefing up your differential, use this guide to understand the differential’s function and what are your options for modifying.
How Differentials Work
Before diving in to modifying your differential, it’s important to understand the device. On the very basic level, the purpose of the differential is to split torque two ways to allow each output to turn at a differential rate.
An automotive differential functions in three roles:
- To direct the power from the engine to the wheels
- To serve as the last gear reduction before the rotational speed hits the wheels
- To move power to the wheels while also allowing them to move at different speeds (hence the name differential!)
So why does your vehicle need a differential? Your truck or SUV’s wheels spin at different speeds while you’re driving. The outside wheels travel a longer distance than the inside wheels. If your vehicle did not have a differential, the wheels would be locked together and forced to spin at the same speed. This would make turning a very difficult task — in order to turn, one tire would have to slip. Modern tires and roads don’t make it easy to lose traction, and it would put a great deal of strain on your axles if this were the case.
Here’s the best video you’ll ever see regarding how differentials work – it is legendary, especially considering how old it is:
Off-Roading and Choosing A Differential
The main concern when it comes to off-roading and your differential is traction. In “normal” driving conditions, free of ice, mud, water, loose dirt, etc., traction isn’t a concern. When things get slippery, the amount of torque delivered to the wheels is limited to the greatest amount possible without slipping. If there isn’t enough traction from the tires and surface, the wheels will slip and spin faster — any off-roader realizes what this means: you’re going to get stuck!
This is why differential upgrades are so popular with off-road enthusiasts. Depending on your needs and your budget, you can choose a differential that works best for your vehicle. Here are the three main options off-road enthusiasts typically consider:
NOTE: Many newer 4×4 vehicles have limited slip differentials as standard equipment, and some even offer electric locking diffs. Therefore, your vehicle might not need an upgrade based on the equipment you have.
Limited Slip Differential
A limited slip differential is based on clutches between the right and left axles. It responds to input torque by tightening the clutches and limited RPM differences between the left and right axle. Application of the clutches is linear and makes it a well-mannered street mechanism with increased traction benefits. Limited slip differentials have a preload that determines the amount of resistance between the axles at all times — this means it’s never truly open. Some units allow for preload adjusting by changing the springs.
This kind of differential is mechanically locked under normal conditions and will unlock under low-torque conditions (like turning). The way the lock-up mechanism is constructed varies greatly from manufacturer to manufacturer, but the function is consistent. A locker is less likely to allow the RPM differences between the tires. These are the top choice for serious off-roaders and rock crawlers who need more than a limited slip differential can offer. However, they may scare off some drivers due to their lack of street manners — they can be heard and felt unlocking when turning and frequently cause the tires to chirp or squeal on slick surfaces.
This is a versatile differential that allows the driver to control the locking and unlocking of the differential. The way the driver controls this function varies by manufacturer. Some units use a vacuum line, electrical circuit, or cable. Manual differentials are ideal for extreme off-roaders and those who want it “all” out of a differential, including total control. Most allow the differential to operate open in normal, everyday driving conditions.
Modifying Your Current Differential
There are other ways to modify your differential other than changing it out completely. Here are the most popular differential modifications:
Welding Your OEM Differential
We’re NOT saying do this, but drivers have been known to weld their stock differential — a very controversial modification. A welded differential has the spider gears welded together in the factory differential. This basically makes for an unreliably locked differential. Should you choose to go this route (don’t), you might want to start saving up for a new differential as soon as you do.
The factory differential cover is not made to protect the internals from the punishments of off-roading. When you take your vehicle off-road, it will enviably encounter the kinds of obstacles and hazards that will likely inflict damage to your cover — therefore causing pricey damage to what’s behind it. To prevent this, upgrade to a stronger cover that will protect the internals – the trail is suddenly a safer place for your ring and pinion set!
New Gear Set
Speaking of ring and pinion sets — this is one of the most popular upgrades and a great place to start (although it’s at the very end). Upgrading your gear set to performance gears means that your gears won’t strip under intense conditions. You can also change the gear ratio to a larger size to help raise your RPMs much faster and get them within your power band.
Note: Unless you’re an experienced gear head, it’s recommended that you enlist the help of a professional mechanic when modifying your differential. They can be complex.