Grease

We are often asked about the frequency or type of grease to use when servicing a drive shaft. The answer has always been; "we believe a frequent and thorough greasing is more important than the type of grease you use". This is primarily because, one of the main results of a proper is a "flushing out" of any contaminates. It seems that a little grease and dirt make an excellent grinding compound. While greasing, if you pump in grease until you see clean grease come out past ALL the seals, you will insure that most of the contaminants will be washed away.

We've taken a look at the lubrication recommendations from some Spicer universal joints (greasable and non-greasable) on my shelf and they read as follows:
 

  • "Spicer Re-Lube Light/Medium Duty..."
  • "Lithium base greases meeting NLGI Grade 1 or Grade 2 are preferred..."
  • "Spicer Pre-Lube Light/Medium Duty..."
  • "Do not add lubrication Do not mix bearing caps on journals..."
  • "Miss-matching of cups on cross will result in improper quantities of lubrication in cups causing premature joint failure..."
  • "Addition of lubricant may damage bearing cup seals leading to premature joint failure..."

The NGLI is the National Grease Lubricating Institute (it's probably a pretty boring place). It is the umbrella organization that sets the standards for the properties of different greases, oils and other lubricants. Again, although we are not authorities on the subject, we do know that the grade will typically refer to the viscosity of the lubrication, with a grade 1 being less viscous than a grade 2. The lithium is the base to which the lubrication is added. In this case, lithium is basically a soap base. There are other bases to which the lubrication can be added, Molybdenum Disulfide for example, which is typically referred to as; a "moly" grease.

Beyond that there are a few general parameters that we would suggest in selecting the grease. Temperature rating should be at least 300 degrees. This may sound awfully high but it wouldn't be uncommon for the drive shaft to reach an operating temperature of near 250 degrees and it's important that the lubrication doesn't separate from the base and boil off.

There is also a load rating to consider. Theoretically at least, if you can prevent metal to metal contact, you will prevent wear. Greases and oils will have what is known as a "Timken Load Rating". We are not qualified to explain all the technical information of a Timken Load Rating, it is basically the rating of the lubricant to withstand certain amounts of pressure before smearing so thin as to allow surface to surface contact. The Timken Load Rating should be sufficient for the intended use. Most grease will probably be adequate with the exception of thin motor assembly grease.

The viscosity should be in the range that will allow for a good flow past all the wearing components while servicing. Again, this is for the "flushing out" of the contaminates while servicing. Very high viscosity in the grease may actually be detrimental as higher viscosity grease tends to create more heat than would a more freely flowing grease. Remember to that ultimately, heat is one of the real enemies here.

If you run in a lot of water or mud, it may also be good to use a grease that has water resistant characteristics.