"A mechanic friend suggested I use CV joint grease containing molybdenum disulfide for the front-wheel bearings of my passenger car. Should I take his recommendation?"
If in doubt about which grease to use in wheel bearings, consult the vehicle manufacturer and/or the bearing manufacturer. In general terms, light vehicle wheel bearings are adequately lubricated with an NLGI (National Lubricating Grease Institute) Grade 2 multipurpose or EP grease with a base oil viscosity of approximately 200 centistokes and meeting NLGI Service Category GC, which covers service typical of wheel bearings operated in passenger cars, trucks and other vehicles under mild to severe duty.
Greases containing moly are recommended for roller bearings subjected to very heavy loads and shock loading, especially in slow or oscillating motion such as found in universal joints and CV joints. If such greases are used in high-speed bearings, problems can be experienced with roller “skidding” where the bearing roller fails to rotate through the full 360 degrees due to reduced friction. As a result, the roller develops flat spots, and its service life is reduced.
In addition, CV joint grease is often manufactured to NLGI Grade 1 and would therefore not be suitable for automotive wheel bearings.