Maintenance Tip: Don’t Forget the Differentials

The engines and drivetrains found in today’s trucks are incredibly powerful and wonderfully complex. In order to keep everything running smoothly, periodic oil changes are required. Failure to perform this maintenance on your truck can result in expensive repairs costing thousands of dollars. Everyone knows how important it is to change the engine oil on a regular basis, but for many owners, the differential’s get scant attention, if at all. That’s too bad, because changing the oil in a differential is important. Like an engine, metal-to-metal contact in the differential creates heat from friction that over time wears down parts. There’s no doubt about it, failure to keep fresh oil in the differential will inevitably lead to a breakdown that could leave you stranded on an outing.

At this point, it’s important to understand what a differential does and where it’s located. If you look at your rear axle, you’ll see what looks like a large pumpkin in the center. That’s your differential. The ring gear and drive pinion inside the differential perform two important functions. One, they transfer power from the driveshaft to the rear wheels. Two, they allow the inside and outside of your wheels to spin at different speeds during turns. This difference in speed is needed because the outside wheel travels farther than the inside. There’s also a front differential on four-wheel drive trucks, but it typically doesn’t get as much of a workout as the one in the rear.

How often should you change the oil in your rear differential if you haul and tow a lot? Every 30,000 miles? Every 60,000 miles? The answer is neither. For those who work their trucks hard, the oil in your rear diff should be changed every 15,000 miles. Why? Because of the work loads we place on our trucks. Hauling around a 3,000-pound camper or towing a 15,000-pound fifth wheel is hard on a rear differential. If you don’t believe me, take a reading of your rear differential with a temperature gun after driving for a couple of hours on the freeway. You’ll be shocked at the number. As for the front differential, unless you use four-wheel drive a lot, the oil in it can be changed every 30,000 miles. If in doubt, consult the maintenance manual for your truck.

When it comes to changing the gear oil in your differential, you have two choices on how to get it done. You can do the work yourself or you can take it to a shop. Doing the work yourself, of course, can save you big money. The AAM axles on my truck take a total of 6 quarts of oil (2 quarts front and 4 quarts rear). At $20 a quart, the total job will cost you $120. That’s much cheaper than the $300 or $400 a shop will charge you. The choice is yours, unless you have a special lifetime warranty that requires that you take your truck into the dealership for servicing.

The Job

If you’ve never changed the oil in your differential it’s actually pretty easy. To do the job, you’ll need an oil pan, a drop cloth, gloves, and the required tools to remove the cover and reinstall it. If you’re lucky, your differential will have a drain plug on the bottom. If it doesn’t have a drain plug, then you’ll need to remove the entire cover to change the oil. Differential oil smells pretty bad so be prepared for the stench. To remove the cover, unscrew the mounting bolts, leaving a bolt on top partially removed to hold the cover in place. To remove the oil, use a putty knife or flat-bladed screwdriver to gently pry open the cover. Let the oil drain completely, then remove the cover.

Thoroughly cleaning the differential after draining the oil is important. If this is your first oil change, you should assume that the leftover oil is filled with metal shavings. Because of this, you’ll want to thoroughly wipe down the inside of the housing and the cover with a rag to ensure that all shavings are removed. Before reinstalling the cover, you’ll also want to ensure that the mating surfaces of the housing and cover are also cleaned using a lint-free cloth and brake cleaner. And speaking of brake cleaner, some owners like to use it to clean the insides of the differential. If you do this, make sure the brake cleaner is fully evaporated before refilling the differential with oil. The last thing you want is any residual amounts of brake cleaner messing with the viscosity of your oil.

AAM 11.5 Diff Cover and Gasket removed from my Ram 3500.

Reinstalling the differential cover and refilling the differential is pretty simple. Most differentials have a gasket, you’ll want to reuse it. If not, then you’ll need to use a liquid gasket product designed for extreme heat and oil exposure like Permatex Ultra Black. Don’t skimp when buying the oil for your differential. Use a synthetic gear oil like Royal Purple. Most newer trucks, including my Ram 3500, call for a synthetic GL-5 SAE 75W-90 gear oil, though some owners prefer to use a heavier 75W-140 oil for the rear differential. Refer to your owner’s manual if in doubt. If you’ve got the clearance, fill the differential directly from the bottle. If not, use a hand pump like the Amsoil G2039. Hand pumps like these are pretty cheap and can be bought any auto parts store. Fill the oil to the bottom of the plug hole until the oil starts dripping out. Reinstall the fill plug and torque it to spec. The job is done.

Aftermarket Differential Covers

The procedure outlined above is primarily for differential’s without a drain plug. The process takes longer and is messier if your truck’s differential doesn’t have a drain plug, but it doesn’t have to be that way. You can buy an aftermarket differential cover that has one. This is what I did. I bought an aluminum AFE Power diff cover (Part. No. 46-70010) for my 2013 Ram 3500 pickup truck. This particular cover is very functional. Not only does it have a drain plug on the bottom and a fill plug on top, but it also has an overfill plug on the side. I also purchased the optional deep reach magnetic fill plug and optional oil level sight glass for the overfill port.

Rear of cover along with O-ring, decals, and instructions.
Closeup of the oil level sight glass.
Closeup of the deep reach magnetic fill plug.
View of installed AFE Power Diff Cover.

As you’d expect, installing the AFE Power differential cover was quick and easy. For the job, you’ll need to use the enclosed O-ring which is basically a rubber gasket that is installed on the back of the cover. Some aftermarket covers may call for the use of the OEM gasket, but not this one.

The AFE Power diff cover is a great addition to my truck. Not only does it look great, but it keeps the oil cooler through the use of cooling fins and a larger reservoir (this particular cover holds 5 quarts compared to the 4 quarts OEM). These features are nice, but honestly, the main reason I bought it was for the drain plug. Having it will make future oil changes fast and easy since removing the cover will no longer be necessary. With rear diff oil changes occurring every 15,000 miles, this time-saving feature will be welcome. I bought my AFE Power differential cover on Amazon.com for $230. This price does not include the oil sight glass and deep reach magnetic fill plug.

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About Mello Mike 534 Articles
Mello Mike is an Arizona native, author, and the founder of Truck Camper Adventure. He's been RV'ing since 2002, is a certified RVIA Level 1 RV Technician, and has restored several Airstream travel trailers. He currently rolls in a 2013 Ram 3500 with a 2021 Bundutec Roadrunner truck camper mounted on top. He retired from the U.S. Navy in 2004 as a CWO3 after 24 years, worked in project management, and now runs Truck Camper Adventure full-time. He also does some RV consulting, repairs, and inspections on the side.

6 Comments

  1. The differentials haven’t really changed much since the 1950s. They had locking differentials in those days too. They have more different types of locking ones today. Ring and pinion gears are a matched set, they are polished together. This goes back even farther.When replaced they must be adjusted in three different adjustments to obtain a perfect gear contact pattern.
    When it comes to aftermarket covers most are not as good as the factory ones. This has been thoroughly tested by automotive engineer Gale Banks. I have been in the automotive industry over 50 years.

  2. I’m glad you mentioned that the large pumpkin in the center of the rear axle is the differential. That is really cool that it allows the inside and outside of your wheels to spin at different speeds during turns. That is really interesting that your wheels can do that. I never thought about how you would have to have different speeds when you turn. Thank you for the information!

  3. The drivetrain on my truck has been making strange noises and this has me worried about how long this will last. I found it interesting that you had mentioned that the drivetrain is very complex in newer vehicles these days. I don’t think I’d be able to handle that myself, I might just have to start looking around for a drivetrain repair company.

  4. It’s interesting to learn that when it comes to fixing a pickup truck that there are some different things we need to consider having done. I like how you mentioned that when it comes to changing the gear oil that there are two ways we can go about doing it to help get it done, either through a shop or do it ourselves. Personally, I think it would be better for us to take it into a shop to make sure that it is done correctly.

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