When you think about your axles and how to make them better, the first things that come to mind are usually gears and lockers. But don't you want to protect those major investments as well? There are a few things that can really hurt a differential: power input with excessive traction but without vehicle movement, incorrect setup, heat buildup, and dirty oil or oil contaminated with water.
There is also the constant danger of a head-on collision between your differential cover and a solid unmoving rock attached to the center of the earth. When this happens the only thing between your new gears and locker and the offending boulder is a few quarts of oil and the diff cover. As the highly technical scientific testing journal that we are, we decided a diff cover test was in order-plus we like to smash things.
The Contenders: We decided to test six Dana 60 covers, being a popular rearend and expensive frontend. From left we have the finned aluminum cover offered by Off Road Unlimited, a clear polycarbonate cover from Clear Gearz, a cast-iron cover from Dynatrac, a cast stainless steel cover from Molten Image Design (this cover can be ordered with or without an oil fill plug), a stock 11/48-inch steel diff cover from Dana Spicer, and a cast-iron Tera 60 cover from Tera Manufacturing. (Tera's cover as tested will not fit a standard Dana 60, but they will soon be offering one made from the same material that does.) We bolted the entire group to 11/44-inch steel plates for real-world testing. This would ensure the covers would not flex and would hopefully keep them from bouncing around under testing.
Our first test was with the Hammatron. This device is similar to an 8-pound sledge with a more scientific name. We gave each cover three direct hits with the same ferocity you would use to smash an approaching rattlesnake. After this first test the stock cover was dented quite badly, the aluminum cover's fins were getting flattened, and the Dynatrac cover lost some powdercoating. The others showed nearly no wear at all, and the Clear Gearz almost killed us when the Hammatron bounced back towards our head where it almost embedded our safety glasses into our skull.
The next test really opened the gap between tough and not-as-tough. At this point we employed the help of renowned axle builder John Currie of Currie Enterprises. He was qualified to help because he didn't have a diff cover in the test, and he is the only person we know in the Los Angeles area with a tracked bulldozer. Currie crushed the competition by crawling over all six of them with his John Deere 555. The covers were close together for the first pass and a few would support the weight at the same time. However, this had no effect on the covers. Then we set them apart to have each cover support the entire weight of the machine's track. This crumbled a few. The Clear Gearz cover caved in, although it may have popped back if there was really a ring gear behind it. There wasn't in our test, thus it rippled and cracked.