Editor’s note: Written by Richard Reina, Product Training Director at CARiD.com
While not the most glamorous or well-known part of your vehicle, the differential gears, usually called the “differential” or just “diff,” is part of the drive axle/final drive. On a traditional front engine/rear-wheel drive vehicle, the differential changes power direction 90 degrees from the driveshaft to the rear axles. It also allows the two rear tires to revolve at different speeds in turns. Four-wheel-drive vehicles have a front diff along with the rear diff. The differential gears have a cover, typically stamped steel, over them. Some vehicles have a drain plug in the bottom of the axle and a fill plug in the cover. Other vehicles may require removing and reinstalling the cover to perform an oil service.
Factory differential covers don’t get a lot of attention from vehicle manufacturers. Most of them are lightweight, but are fine for day-to-day driving. However, if you take your truck or SUV off-road, your vehicle’s differential internals, gear oil, and protective cover are all subject to greater stress, higher temperatures, and damage from external influences. One of the easiest and most cost-effective ways to provide additional protection is an upgrade to a performance diff cover. If your rig is lifted (and if you’re off-roading, it likely is), the differential is more exposed, and a dressier cover can also add some ‘bling’.
When shopping for aftermarket differential covers for an off-road vehicle, you can consider upgrades based on three distinct improvements: cooling ability, impact protection, and of course, style.
KEEP YOUR COOL!
The harder or faster you drive your vehicle, the more it is subject to elevated temperatures. This is as true for the differential as it is for any other moving parts of your truck. Like engine oil, diff oil both lubricates those parts and dissipates heat from them. Keeping temperatures in check helps ensure the longevity of the gears and bearings.
An upgraded differential cover helps with cooling in one of three ways. The first being the material itself: aluminum covers will expend heat very well. Aluminum also has a weight advantage. Compared to steel or iron ones, diff covers made of aluminum are also significantly lighter.
A second way that a cover can help keep things cool is by design. A finned cover has a greater surface area, so no matter what the material, it will shed heat more quickly than a non-finned cover. Picture the cooling fins on an air-cooled engine and you’ll get the idea.
The third way a cover can help is by increased oil capacity. A larger cover can hold more oil; that greater amount of oil gives it a greater chance to carry away heat. The more oil there is, the more heat it can shed.
PROTECT YOUR GEARS
The main function of a differential cover is right there in its name: it needs to adequately cover the gears to prevent dirt, dust and moisture from reaching them and the fluid within. If you’re roughing it off-road, where you’ll likely encounter dirt, sand, mud, flying rocks, massive boulders and water (both standing and running), and having a strong yet protective differential cover can make all the difference.
A factory cover of thin stamped steel just won’t hold up well to direct hits. Once it’s dented or scraped, oil may seep out, or it may flex and fail further, allowing debris in. Either way, your diff could fail, which is an expensive fix!
Serious off-roaders should consider heavy-duty diff covers. Cast-iron covers offer tremendous strength advantages over OE covers, at the expense of added weight. Don’t neglect to consider heavy-duty aluminum ones, which get their strength from their thickness, while still providing weight advantages over cast-iron. A beefier cover not only can take the knocks; it can also serve as a brace for the differential housing itself.
Perhaps the ultimate in additional strength are performance diff covers which include load bolts. These bolts are tightened up against the differential bearing caps during installation, further bracing the entire assembly from deflection under severe loads.
SHOW OFF YOUR STYLE
Now that we’ve covered some of the more technical reasons to add a performance differential cover, let’s talk about style. There are countless ways to upgrade your truck or SUV to show off your personality, particularly if you use it for off-roading. With all the lights, racks and tire upgrades out there, customizing something like your differential covers might not be the first thing you think of, but there are some cool and dressy options available if you want an added flair!
On a lifted truck, the diff cover is one of the few “greasy underside bits” that’s easily spotted, so why not call attention to it? Cast-iron ones can be painted or powder-coated in almost any color. Two-toned finned covers are both highly functional and make a strong styling statement. Aluminum can be polished to a high gloss, and for the ultimate in gloss, consider a chrome-plated cover.
For many drivers, differentials and their covers fall into the “out of sight, out of mind” category. They are hidden beneath the vehicle and only get attention when serviced by a mechanic. Regular drivers with ordinary cars might not even know that they are there! However, if you’re a proud SUV or truck owner looking for upgrades to withstand off-roading treks, you shouldn’t overlook differential covers. A performance cover offers significant advantages which could make all the difference the next time you hit the trail!
Editor’s Note: Richard Reina is the product training director at CARiD.com and an auto enthusiast and expert with over 30 years of experience working with cars and trucks.