Be kind to your differential — It’s all you’ve got


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.

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 — 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 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.

photo: Wikimedia

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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