Some historic military vehicle service and maintenance tasks are so mundane, boring or dirty that we sometimes just put them off. Common examples are lube jobs, checking and/or changing the gear oil in transmissions, transfer cases and axles, and draining, flushing, and renewing the engine coolant and brake fluid. Ironically, it’s often the dirty, boring, and relatively simple maintenance duties that do a lot to keep our vehicles on the road, in good mechanical condition, and ensure that they have a long and dependable life. At the top of many don’t-wanna-do lists is servicing a vehicle’s air cleaner.
Back in the early days of Military Vehicles Magazine I started the question-and-answer “Tech Tips” column, and one of the first letters I received was about an oil-bath air cleaner on an M38. The question was: “Where does the extra oil come from to raise the level in the oil cup from Normal to Service?” My answer was (and is) that the oil level doesn’t rise because extra oil mysteriously appears, but rather because of dirt and dust particles – sediment --collected by the air cleaner, which settle to the bottom of the oil cup.
Answering this and other questions about air cleaners (or air filters, if you prefer) is what this article is about. In past articles I’ve mentioned various vehicular components that seem shrouded in mystery in regard to how they work or what their useful purpose might be. I’ve also written about components that seem so long-lived and trouble-free that their service is often overlooked until they finally wear out and fail. Wheel bearings and universal joints are two examples. But, after sixty-some years experience, I would have to say that the most universally-neglected and least-serviced component of many vehicles are their air cleaners. In fact, I would bet that the air-cleaners on about 80 percent of the world’s vehicles need servicing at this very moment, and probably also a few simple and inexpensive repairs, because they’re dirty and/or otherwise not functioning properly.
One of the major differences between components such as universal joints and air cleaners is that when a universal joint fails it’s often suddenly and may leave one stranded somewhere, whereas even total failure of an air cleaner --such as being so clogged with dirt that an engine won’t run --is seldom a sudden occurrence. Basically, when an air-cleaner fails, an engine only wears out faster. This wear is accelerated if a vehicle is being used in dusty or dirty environments.
I was once doing a demolition job in Central California, operating an ancient Allis-Chalmers bulldozer
