4x4 - Home

U-joint Lubrication

Shortly after I had installed my Tom Wood front drive shaft, I came across an on-line forum thread that was started by a friend of mine.  It dealt with his front CV drive shaft rebuild.  Somewhere along the line, the discussion got around to u-joint grease and what was appropriate for the application.  I had never given the topic much thought as I have used a synthetic grease (Mobil 1) in my grease gun for years.  Some of the comments in the thread left me wondering about proper u-joint lubrication. 

I dropped Tom Wood an e-mail to see what his views on the subject might be....after all, Tom should have some insight into this since he makes a living from building drive shafts that are full of u-joints.

Here is part of Tom's response:

I get asked this question often and the answer has always been that; "I 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 lubrication 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.

I'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" * ar (ours´┐Żobvious miss-spelling)

The NGLI is the National Grease Lubricating Institute (I' ll bet it's 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 I am not an authority on the subject, I 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 I believe that 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. You or your readers can get all the information they need or want about the specific properties of each grade and designation of greases at this web site.

Beyond that there are a few general parameters that I 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 ~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". While I'm 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 greases 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 greased tend 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.

First, I want to thank Tom for taking the time to respond to my e-mail.  I appreciate the comments and viewpoint from someone who has been in the business for a while. 

Armed with some info from Tom, I hit the internet and did some digging around.  I found that the "NLGI Grade" that Tom mentioned runs the range from Grade 000 to Grade 6.  To give you an idea what this range includes, 000 is semi-fluid (pourable) grease while Grade 6 holds its shape and is too hard to be worked.  Grade 2 is the most common grease grade and Grade 1 is slightly softer than Grade 2.  If the grease is too stiff, it will may not feed into areas requiring lubrication.  If the grease is too fluid, it can leak out.  Either situation can result in damage to the components that are depending on proper lubrication, like the needle bearings in your u-joint.

My friend that had started the forum thread was told by the shop he got his parts from that the grease used on the u-joints should be extreme pressure rated.  The more I dug around the NLGI web site, the more I realized that Tom's comment about that place being pretty boring was oh so true.  Don't do a search on extreme pressure, you'll find more info than a normal person could handle in a life time.  Let's just say that you want a grease that exhibits good extreme pressure qualities....I'm not sure how that is measured just yet....and I'm not going to try to find out either. 

So after a bit more poking and prodding with the web browser, I finally surfed over to the Mobil1 web site to see what I could find out about the grease I was using.  Over all, I was pleased with the results, based on what I had seen on the web and gotten from Tom's e-mail.  I found the following:

I've no doubt that if you go to other lubrication manufacturer's web sites, you will find similar data stating that their products are good.  

I know a little more about grease now then I did earlier today.  According to Mobil1's web site, the grease I am using should work well for everything I use it for.  And I plan on following Tom's suggestion about properly "flushing out" the contaminates that may get into the components. 

Some night, if you find yourself at the edge, and counting sheep is looming on the horizon as the only way you may fall asleep, try surfing on over to the NLGI web site and so a search on extreme pressure.  If you make it through the first white paper without falling asleep, maybe you should consult the services of your family doctor......I think you may be suffering from a severe sleep disorder.  <grin>




4x4 Off-Road    Homestead    Firearms    RC Flying