Friday, February 3, 2023


Be kind to your differential – It’s all you have

By Greg Illes
Deep down under your rig, far behind the driver’s seat and usually caked with dirt, grease and road grime, is one of the most critical members of your drive train – the rear axle and its differential.

From Wikimedia

Whether you drive a motorhome or pull a trailer or fifth wheel, you and your entire load rely on that rear axle to propel you down the road. Every single pony of your engine’s horsepower must route through a compact cluster of incredibly tough gears in order to twist your axles, spin your tires and push you up that hill or across that valley.

Although these units are pretty reliable, they are not maintenance-free. Sure, everybody checks their engine oil, transmission fluid, engine coolant and all the usual “stuff” to keep the beast running. But how often does anyone check the “rear end”?

In our heavily loaded rigs, the differential gets a heavier workout than in any street automobile – really more comparable to a working truck. Tender loving care (TLC) is very appropriate and can take several forms.

Leak checks of the differential

There’s no “dipstick” on your differential. The precious gear lube inside is all that keeps those wheels turning. Visually check the axle now and then, both at the center and out at the inside of the wheel hubs. If you see any signs of grease leakage, it means that some of that fluid is gone. Check the fluid level by removing the fill plug and sticking your finger inside; the fluid should be nearly up to the plug hole. If the leakage is any more than a very slight seepage, seals are beginning to fail and it’s time for a serious inspection.

Periodic fluid changes

Check your owner’s manual and be sure to have the rear-end fluid changed at least as often as stated. Run the best fluid you can buy. Most axles love synthetic fluids, but be sure to use a manufacturer-approved product. If you’ve had the axle in extensive dusty conditions or fully underwater, change the fluid right away.

After-market differential covers

Many axle models have after-market differential covers available. Don’t think that these are just for the hot-rodders or teenagers. These oversized, finned aluminum covers provide for extra fluid capacity, and the fins create additional cooling surface. Your differential fluid, and all your components, will run cooler with this add-on. Cooler is better, and your gears and bearings will thank you.

The bottom line is to be aware of, and sensitive to, the critical work done by that rear axle. Take care of it, and it will continue to take care of you.

Greg Illes is a retired systems engineer who loves thinking up RV upgrades and modifications. When he’s not working on his motorhome, he’s traveling in it. You can follow his blog at

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1 year ago

I find the short articles by Greg Illes well written and educational.
However, this Newby never worked on cars growing up, and just bought a big DP as first RV.
Therefore, adding some photos or diagrams to supplement those articles would help immensely.

1 year ago

My wife and I have a 18 foot senior couple travel trailer pulled by a 07 Jeep GC with the 3.7 V6. Every spring before camping season starts the Jeep goes to the local Chrysler dealer for a check up. This year not only fluid levels, brakes, etc new replacement shocks and load leveling bump stops are being installed. We are going to Yellowstone for 2weeks and anything we can do to make our trip trouble free, yours in RV ing, Ray and Joy.

Robert Cross
1 year ago

Banks does a real good testing of Different Diff Covers. Eye opening.

1 year ago

I replaced my diff cover with a finned aluminum aftermarket version. It has a drain plug eliminating the mess from a fluid change and it even has a small window to visually verify the quantity and quality of the fluid. One brand does have a dip stick.

1 year ago

When I bought my truck I had the engine bulletproofed so I wouldn’t have any problems pulling my 9000 pound travel trailer.
When I bought the 18000 pound fifth wheel I put on a finned differential cover that added another quart of fluid. Plus an SCT engine tuner, stage 1 turbo, coolant filter, high flow engine oil cooler, cold air induction, 1/2 step larger injectors. Exhaust Gas Temperature gauge, high flow dual exhaust system, studs on the heads, 250 amp alternator, drilled and slotted brake disks, enhanced engine braking system, and an extra 72 gallon fuel tank. Now all I have to worry about is keeping my foot 🦶 off the dang accelerator pedal.

David Telenko
1 year ago
Reply to  bisonwings

WOW, sounds more like a RACE engine preparation, I know I’ve done it with even more done to my engine! Yours should live long with enough power for that 18K fiver!

Ian Anderson
1 year ago

My 1999 F-53 came with synthetic oil in the differential case. Ford says it is good for life. I did change it out at about 50,000 miles. It takes 12 quarts of 75/140w oil which is quite expensive..

Bob P
1 year ago

In a way this could be misunderstood as a commercial but it’s not intended to be. Gale Banks engineering did several YouTube videos on differential covers, their design, styling, etc. In the end it showed how they designed their cover but the main part was about how inefficient most covers are at providing good circulation and cooling, I found it interesting as well as informative. You might say if it matters why doesn’t the factory use a better cover, well simple answer cost. The factory cover is a stamped steel that they make one every 3 seconds, and as long as the oil does it’s job through the warranty period that’s all that matters.

1 year ago
Reply to  Bob P

Gale Banks makes parts that actually work. The YouTube videos provide great information.

1 year ago
Reply to  Bob P

Banks at least analyzed and tested differential cover ideas and designs instead of just assuming more oil is better and then producing an easy to manufacture square cornered cover. Some RAM one tons come with an finned aluminum cover that is very similar to the Banks design except for the air scoops. I found one for about $100 on the internet to put on my RAM 2500. I did it mostly because I like the “bling,” like most of us that have added decorative covers.

Tommy Molnar
1 year ago
Reply to  Bob P

Banks finally came out with his own scientifically designed diff cover and demonstrates how and why he is better than the competition. I have a Banks iDash gauge in my 2016 F-350. This little piece of engineering marvel is fabulous! It can be set up to monitor every sensing unit in the truck. Over the years I’ve installed many of Banks’ offerings and have had good luck with every one of them. I totally trust anything that Gale Banks offers.

Marty chambers
1 year ago

Well written Greg, the Punkin and brake fluid never get thought of by many.

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