MoS2 and needle roller skidding

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I believe in it, but don't know parameters or quantities.

One of my most interesting experiences was messing around with a really large spherical roller bearing, at quite a high speed, and with very low loading for its size.

Ran really hot, and wore out quickly, and was diagnosed as rollers skidding...was purely a bearing design issue.

Moly disulphide, I imagine as discrete particles in suspension, rather than dissolved liquids, making the relative difference in size hugely massive, and akin to a gravel stop versus sliding on ice.

Maybe.
 
Skidding occurs when a lightly loaded bearing sees high angular acceleration, or when the rollers in a lightly loaded bearing run in and out of a preload condition around the circumference.

MoS2, per se, does not give rise to skidding damage in a bearing.
 
I was taught that that the solid particles sort off being ground up under the roller bearing as "normal' debris will cause depending on load and speed micro pitting, spalling then failure.

bruce
 
Technical papers exist which say it is a fact, not fallacy that MoS2 is not recommended for needle bearings.

And I believe the evidence of my own eyes in that years ago I saw many more needle bearing failures which involved the use of MoS2, and that now that I do not use it in needle bearings, I haven't had a single failure. MoS2 will never see any of my u-joint spiders.

My trucks require MoS2 in the propeller shaft splines, but specifically warn against it in the u-joint spiders, and I adhere to this.
 
U-joints don't experience skidding. Their operation is considered "micromotion". The original poster asked about skidding, which strongly implies that the bearing experiences full rotation with many rpm's and thus two different lube requirements between the two applications.

Can MoS2 be considered "debris" in the classical sense? It certainly can't be compared with hard particle debris. The crystalline structure of MoS2 is unique in that it slips easily, which gives it the properties of a solid lubricant. And I imagine even MoS2 can be finely divided enough during roller bearing operation that it would reach a particle size that is smaller than the separation distance between the rolling elements, and not be considered particle debris in bearing life calculations.

I don't argue that it shouldn't be used in u-joints. I'll defer to what Sylvatica has read and experienced.
 
What I saw happening in the needle bearings of failed u-joint spiders appeared to be the lubricating oil in the grease was centrifuged outward and expelled. The moly remained with the grease thickener, and built up into a thick, non-flowing paste. I can imagine that the MoS2 platelets were coalescing and accreting onto the needles, and to spin the needles had to plow through the dried moly buildup. This was too much for a boundary lube and nowhere near the correct viscometric flow for a hydrodynamic regime.

The u-joint is not like a bigger scale bearing situation, or a shock loaded application where I would certainly pump in the moly.
 
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So would a better blended grease with better components: base oils, moly,thickeners, etc change the equation?
 
U-joints are a micromotion application that requires not a thick grease, but rather a thin grease. The idea is that you want a grease that is thin enough to reflow under the needles after it is pushed aside.

Kluberplex BEM 34-132 is probably one of the best greases out there for automotive u-joints. It's a calcium-based NLGI Grade 1.5 that is heat resistant and long life. I forget the times and temperatures, but it equates to roughly 100K automotive use.
 
Interesting conflicting advice.
I live in the mountains located in Massachusetts’s Berkshires and bought a new 4x4 Cummins Turbo Diesel in 1990. I started using moly fortified grease in 1992 which at that time was recommended for mining and construction equipment and have had no grease related issues.
This truck had a 5th wheel and I pulled a 28ft flat bed moving small equipment and logs. On 1 occasion I had a load of 3/4 stone with a gross weight of 22,500.
The stone was for a home project otherwise I never would have attempted it. Needless to say it was far more that he truck was rated for and in-fact could not be safely stopped but I was only interested in getting this home which I did.
The point here is that I used moly fortified grease in the u-joints and these original u-joints are 20 years old and have close to 320,000 miles on them and are still in use.
I do grease regularly.
Moly is my preferred grease for all chassis locations.
Obviously 1 success story does not mean it is the best grease but it works for me.
Tim
 
Originally Posted By: Sylvatica
What I saw happening in the needle bearings of failed u-joint spiders appeared to be the lubricating oil in the grease was centrifuged outward and expelled. The moly remained with the grease thickener, and built up into a thick, non-flowing paste. I can imagine that the MoS2 platelets were coalescing and accreting onto the needles, and to spin the needles had to plow through the dried moly buildup. This was too much for a boundary lube and nowhere near the correct viscometric flow for a hydrodynamic regime.

The u-joint is not like a bigger scale bearing situation, or a shock loaded application where I would certainly pump in the moly.


Is it possible that the grease just had a problem with oil separation and you were looking at the "coked up" remains of the thickener/additives?
 
Hmmm...my Tundra has had Schaeffer's syn-blend #2 moly grease in the u-joints for the last 90,000 miles. When should I expect them to fail? The manual calls for moly grease in the double cardan joint, which I believe is a pair of needle-bearing u-joints. The other u-joints and spline have just a lithium base grease specified, but all get moly.

If the oil centrifuged out of the needle bearings, wasn't that a failure of the grease to hold the oil? Which grease with the oil centrifuged out would have allowed those bearings to live longer?
 
Interesting.

I've always used Castrol LMM for chassis lubrication, and that involves the uni's.
So for nearly thirty years now I've pumped an NLGI #2, 3% MoS2 fortified Li complex grease into every universal joint I've serviced without having to replace any for bearing wear (yet) and some of those joints have had upwards of 500,000km.
The current longest living ones are at 320,000km.

It was some years back that someone on here warned against MoS2 in unis specifically, their experience was a large mining operation where they had wholesale universal joint failures after they specified a moly fortified grease for maintenace.
It had bitten them on the arse big time.

This surprised a few of us here, and for whatever reason it still rattles around in my head (I don't like doing things wrong :D ) so I thought I'd bring it back up to see what experiences people have had.

Could it be a case of the 3% additive level sneaks by, yet the CAT/mining specced 5% is a touch too much for this application ?

Thanks for the feedback.
 
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I recently got a tube of Cat Desert Gold, which is 5% moly, and it states right on the tube that it is formulated for use in high speed applications as well as pins, etc.
 
Originally Posted By: Tempest
I recently got a tube of Cat Desert Gold, which is 5% moly, and it states right on the tube that it is formulated for use in high speed applications as well as pins, etc.


That it does. I was only reading the PDS a day or so back.
I tried getting my hands on some of that here years ago, and the bloke on the counter at the CAT dealer went "Huh ?"
smirk2.gif
 
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