So, while this thread really has nothing at all to do with M151s per se, you are going to notice some similarities in the manner in which we hash things out on these forums and you may be surprised how some people habitually cling to time-worn lines of thinking
(that may just be wrong and leave us asking all the wrong questions), and the problems associated with 'Group Think' and the fascinating array of options that modern chemistry has presented us with, particularly in dealing with old trucks. So, here we go.
I title this -
Steering Knuckle Lubrication - The Great DivideThe Tech Manuals for the M38 call for specific lubrication within the steering knuckle called, GAA , "Grease, Automotive and Artillery." This lubrication is introduced into the steering knuckle through a hole that is blocked off with a pipe plug, much like those we find on most differentials and manual transmissions. The reason for this is to allow you to see that you have a proper amount of lubricant in there. Just like your differential, the fill line is the bottom of the plug hole.
Well, what if I told you that GAA has given way to new types of lubrication and has become an anachronism? What if I told you that it is no longer being used by the military which has found something other than (and very likely
better than) GAA to use? What if I told you that the people who have purchased these surpluses of GAA are charging an arm and a leg for it or quite often, will only sell it in bulk amounts. And, what if I told you that rigid adherence to the time-worn and erroneous idea that the information in the Tech Manuals was brought down from the mount by Moses (along with the ten commandments) is entirely the
wrong way to think about things with the many options available to us? Two schools of thought - GAA is sacred stuff -or- GAA is not sacred stuff. Two schools of thought, hence our title
The Great Divide.
Crusty old salts who, if they had their way, would have us
still enjoying the company of our equine friends, give us their short answer, "Suck it up buttercup, go source some GAA grease, bust out your wallet, do what the book tells ya and tell yer mama I said hello." My response is, "Well, sorry Charlie, I've never been much of a joiner." In saying that, I'm left feeling like I'm left standing on the precipice of a great chasm, staring over at the other side where all the other happy little boys with their golden cans of GAA are standing and they, staring back at me, see me standing there with my tube of "
other-than-GAA lube", while waiting for me to step forward and fall into the depths. It's a lonely, sometimes scary place..
This all began with something quite simple. If you have been following along, you have seen how the steering knuckle is assembled with the king pin bearings living in the same space with the axle's universal joint and thus, inevitably sharing the same lubrication, especially with the lower king pin bearing fully submerged. And yet, I was getting advice from old sages who were telling me to lubricate the king pin bearings with wheel bearing grease. Wait!
WHAAAAT?!! What happened to the use-GAA-or-die-a-horrible-death thing?
Over the years, some of the original perspective on these assemblies has been lost to the sands of time. The old mechanics pack up their tools one last time and go home, and the new mechanics, when faced with old technology, go with what they know. Such as - a cone bearing must be "packed" and packing involves wheel bearing grease, which is thick, ergo - cone bearings all get wheel bearing grease. Eventually it becomes a sort of institutional group-think and I submit to you that George Patton Jr. put it best. "If everybody is thinking alike, then
somebody isn't thinking!"
Now, they both may be cone-type bearings but they do
entirely different jobs - wheel bearings are employed at relatively high speeds with 360 degrees of revolution on a vertical plane in a small space where they have only the lubrication they were packed with whereas, king pin bearings are employed at almost NO speed, in a large space where they enjoy almost constantly refreshed lubrication, and are moving only a few degrees at a time on a horizontal plane. They generally look the same and that's about where the similarity ends.
And the principle that a layperson should not blindly mix lubricants is sacred law. Ask any chemist.
So I did! Three hours of hashing this out over the phone. THREE HOURS!
I happen to have a buddy, now retired, who spent his professional career as a chemist. Working for Uncle Sam, it was his job to make sure that military vehicles and all sorts of things associated with military vehicles were using the correct stuff. Some of that stuff had wheels and some of it had wings and some of it was so specific that using the wrong stuff meant having to send very expensive pieces back to the factory for re-coating or writing the parts off altogether.
So, I knew when I made the phone call, that his having over twenty years of saying, "Use only what the book tells you to use." would result in getting the
suck-it-up-buttercup answer. Oh! I learned a
lot about lubrication and a lot of it based on the chemistry of the stuff. Stuff that I felt I needed to know to make some informed decisions because I felt GAA was going to be out of reach for several very practical reasons, not the least of which was
availability, not only roadside, but also in the long term. We also reaffirmed that mixing lubricants was still a no-no and could result in some rather serious consequences, particularly when mixing lubes actually degrades the lubricity (I LOVE that word because it sounds so dirty) to the point where it no longer lubricates. He presented that to me as what I would call
"a dire warning", so if you do this, you do it at your peril.
But were we approaching the problem from the right direction? We weren't any closer to solving the problem than when I dialed his number. Were we asking the right question? Because
sometimes, folks, it isn't always about Mil Spec. Sometimes it's better to work the problem from the
civilian perspective.
So, after two hours of chatting, I finally challenged my chemist's standard answer with a simple statement of fact. The M38 has a
civilian counterpart using the same front axle group - the CJ3A and, in fact, that axle group (with some minor changes) was used until something like 1971. They don't use GAA but you can bet they using something very similar! So, when I laid
that on him....
KaBOOM! (His head explodes) Stoney silence at his end of the line while he scooped his brains back into his skull.
NOW, the answer was that it would then be okay to use an OEM-approved lubricant. And suddenly, HALLELUJAH!.... the clouds parted.
Luckily for you, dear reader, I am prepared to share with you the straight skinny.
In order for one to find a certified civilian counterpart to GAA, the only bonofide presented on greases that meet GAA specs are markings, either the NSN number for GAA (which changes depending upon the size of the container) or the Mil-PRF number for lubricants with the properties of GAA, and actually finding one on the shelves of most big name auto parts stores is...well, let's just say you'd have better luck finding a unicorn in your sock drawer under the Valentines Day card you forgot to give to your wife.. In short,
forget it. Ain't gonna happen and let's face it, you aren't going to drive a hundred miles to a big manufacturer with a huge warehouse of lubricants and ask for two tubes of the stuff even if they
did have it. Again...ain't gonna happen! How do I know? I spent hours and hours reading labels at many, many stores. Hours and hours of my life that I'll
never get back.
So I asked another question of NAPA, O'Reilly's, Auto Zone and even the Jeep dealership. What was used back then? What was the OEM lube of choice? Nobody knew and the guys at Jeep, likely in an effort to save face (or perhaps with a more noble cause in mind, such as shooing the annoying old guy out of their dealership) waved a tube of very generic chassis grease under my nose and said,
"This is IT!" (which was
totally wrong) and frankly, none of them had even been
around in 1971.
By this time I figured I was going to be completely on my own...it was sink or swim. So, what to use? Here are
my parameters -
(1) I want to put the stuff in and forget about the whole affair...maybe forever...because it hurts my brain.

I want what is an essentially fire-and-forget lubricant. Something that lasts longer and is better than just plain, everyday, run-of-the-mill grease. I want
modern chemistry in my 1951 Jeep!
(2) Because of that, I want something that isn't prone to creating oxidization and other problems for the truck or for the next guy. That left out some very popular lubes which use some very popular chemistry and which, if you knew about it, would probably have many of you scrambling to change out your lubrication. (see line 1).
(3) And I want something that is typically on the shelves of most auto parts stores. If I need to do a roadside repair I want it to be
available (which, naturally, totally rules out GAA).
(4) Because I am running an old truck with a good degree of wear and thus a good deal of slop in worn parts, I want a lubricant that resists squeezing out, has good adherence qualities but also has good flow (NLGI #2 - which is generally, the equivilent of peanut butter)
(4) I want something that is sticky and resists slinging but isn't sling-proof because the very first goal is to keep the axle's universal joint well lubricated ...but also to get
some lubricant slung onto that top king pin bearing.
(5) And I want something that doesn't thin out when it gets hot. In fact, I want something that might even get thicker when it gets hot.
(6) I want something that is not hydroscopic or prone to washout.
(7) And I want something that meets or exceeds the performance requirements of the manufacturers of
really darned expensive farm equipment.
In short, I want it ALLAnd parameter number 7 is what brings us back around, full circle to the topic of what questions to ask. Are we coming from the right place when we are looking for solutions? We started with Mil Spec, then on to general OEM automotive spec and now, to general OEM farm spec which I think you will quickly agree is a
VERY good place to be!
Farm equipment generally has all sorts of things going on when they're in use. They sit for long periods of inactivity, they have high speed, low speed, no speed parts, they are operated with huge variations in temperatures and they are expected to perform under the worst conditions with the least amount of necessary maintenance. Hmmm...that kind of sounds like our old trucks, eh?
By now you're probably waiting to hear what I've selected as my steering knuckle lubricant. C'mon TJ! Let's have it! Well, you're going to have to wait for the big reveal. I think I have the stuff but, at the risk of another three hours of lecture, I have to run it by my chemist first.
Cheers,
TJ