In The Shop: Grease Gun Guidelines
Jan 22, 2012
Using a grease gun is not a mindless maintenance routine. Done correctly, it takes at a bit of knowledge and attention to detail to ensure optimum benefit.
First, be sure the gun is filled with the right kind of grease. Any grease is better than no grease, but certain types of grease work better in specific applications. "Moly" greases work well under extreme pressure, and are sometimes preferred in situations where mechanical parts rock back and forth rather than spin in full circles that keep the grease distributed. Lithium-based greases resist "wash out" from water, but not as well as greases labeled as "waterproof," which are recommended in places frequently subjected to immersion (boat trailer wheel bearings, ATV wheel bearings on ATVs that cross a lot of streams, etc.). Synthetic greases are extremely heat resistant, very waterproof, excellent lubricants that are nearly miracle-workers, but are so expensive that they may not be cost-effective for normal use. Use synthetic grease in situations where extreme heat, extreme pressure or extreme cost of repairs justify the higher cost of that lubricant.
The current go-to grease for general use on farm equipment is polyurea-based grease. Polyurea greases exceed most of the lubrication, temperature, moisture resistance and other baseline requirements. Unless the owner's manual specifies another type of grease in a particular place on a machine, polyurea grease is probably the best all-round grease to keep in a farm grease gun.
The grease gun itself makes a difference. I prefer hand-operated grease guns for daily maintenance. Air- or battery-powered grease guns are okay for filling gearcases, but I'm uncomfortable with their lack of "feel." It's possible to overfill with grease a bearing or bearing housing. Too much grease can pop off the bearing seals, and in some cases excess grease actually increases bearing heat because of "churning." That's why I prefer a hand-operated grease gun--when I feel resistance I know the bearing is full. Powered grease guns keep pumping until the trigger is released.
One exception to the rule of "stop greasing before it's full" is a universal joint. The seals on a u-joint are one-way seals, designed to purge excess grease. Pat Fagen, u-joint guru at the Axle Exchange in Des Moines, Iowa, recommends greasing conventional u-joints until you can hear grease "popping" from the seals, or until you can see traces of grease at each of the four seals on the u-joint's "cross."
I'll post more greasy goodies in my next post.