What You Need To Know About Grease

Q: I shot a bunch of expensive marine-style grease into the bearing buddies on my bass-boat trailer last fall. It was recommended to me by a marine mechanic as the best product for my trailer, because the wheels get dunked regularly, and this particular type of grease is supposed to be more water-resistant. I finally got a chance to go fishing last weekend and noticed that the grease cups had all leaked oily snot all over my brakes. So instead, I spent the afternoon cleaning and repacking all six wheel bearings and replacing all of the greasy, oily brake shoes. Can you suggest a brand of grease that won’t do this?

A: You mentioned the brand of grease in your letter, which I removed, because it's a perfectly good product, and the correct one for your application. Specifically, i t ' s an aluminum-complex grease, and this type of grease has excellent performance when there's a chance of water contamination, like on your trailer.



A primer about grease: It's basically nothing more than a heavy oil mixed with enough soap to make it stringy and clingy enough to remain in place as the bearing spins. This will ensure the bearing's rollers or balls are constantly covered in the oil. The soap is based on a variety of compounds, notably lithium or aluminum complexes for most of the greases used in cars, trucks and boats.



Problem: Not all the soaps are compatible with each other. This causes the soap and the oil to separate, letting the latter settle to the bottom of the cavity the bearing is in. No surprise—a lot of grease caps have a poor metal-to-metal seal and will let the oil leak out after some weeks. Like yours did.



Your wheel bearings were probably originally lubed with a lithium-12-complex grease, a perfectly good grease for wheel-bearing use, even on a boat trailer if it’s maintained. Shooting some more grease into the bearing cap with a grease gun isn’t a bad idea. Shooting an incompatible grease in is.



This counterpoints the need to completely remove the last vestiges of old grease from a bearing whenever it's repacked. Yes, you want to remove the dirt and wear particles, but odds are you won't know what kind of grease the last mechanic used.



I'm not going to print a huge grease compatibility chart here, although that kind of information is available on the Internet. If you always clean the bearings properly before repacking, it will never be a problem.



Don't have a nice parts-washing sink with recirculating solvent handy to your driveway? It's still easy to clean the bearings properly. Remove the bearings, inner and outer, and any shims, lockwashers and clamp nuts. The bearing inner or outer races can stay pressed in place, however. Scrub the inside of the bearing cavity with paper towels until you've got as much grease out as possible, and wipe as much off the bearing itself. Dump the used paper towels. My favorite bearing cleaner for the field is a disposable aluminum pie tin, but any suitable vessel will do. One at a time, clean the parts in solvent, whether it's turpentine, paint thinner, kerosene or even hot, soapy water in a pinch. Keep the bearings separate so they go back into the same wheel-don't mix and match. Use a cheap disposable paintbrush to scrub all the old grease out. Let dry, then finish with a quick blast of carb or brake cleaner to get the last dust off. If you have compressed air, you can use it to dry the bearings as long as you don't spin them into destruction. Pack the bearings by hand, and fill the cavity approximately halfway with grease.