Address:No.7 Xinye Road, Jinyun
Industrial Park, Jinyun County,
Zhejiang Province, China
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 compatiblewith each other. This causes thesoap and the oil to separate, letting thelatter settle to the bottom of the cavitythe bearing is in. No surprise—a lot ofgrease caps have a poor metal-to-metalseal and will let the oil leak out after some weeks. Like yours did.
Your wheel bearings were probablyoriginally lubed with a lithium-12-complexgrease, a perfectly good greasefor wheel-bearing use, even on a boattrailer if it’s maintained. Shooting somemore grease into the bearing cap with agrease gun isn’t a bad idea. Shooting anincompatible grease in is.
This counterpoints the need to completelyremove the last vestiges of oldgrease from a bearing whenever it'srepacked. Yes, you want to remove thedirt and wear particles, but odds areyou won't know what kind of grease thelast mechanic used.
I'm not going to print a huge greasecompatibility chart here, although that kind of information is available on theInternet. If you always clean the bearingsproperly before repacking, it willnever be a problem.
Don't have a nice parts-washingsink with recirculating solvent handy toyour driveway? It's still easy to cleanthe bearings properly. Remove thebearings, inner and outer, and anyshims, lockwashers and clamp nuts.The bearing inner or outer races canstay pressed in place, however. Scrubthe inside of the bearing cavity withpaper towels until you've got as muchgrease out as possible, and wipe asmuch off the bearing itself. Dump theused paper towels. My favorite bearingcleaner for the field is a disposable aluminumpie tin, but any suitable vesselwill do. One at a time, clean the partsin solvent, whether it's turpentine,paint thinner, kerosene or even hot,soapy water in a pinch. Keep the bearingsseparate so they go back into thesame wheel-don't mix and match.Use a cheap disposable paintbrush toscrub all the old grease out. Let dry,then finish with a quick blast of carb orbrake cleaner to get the last dust off. Ifyou have compressed air, you can useit to dry the bearings as long as youdon't spin them into destruction. Packthe bearings by hand, and fill the cavityapproximately halfway with grease.