MoS2 in manual transmission

[kilou]

Quote:

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From personal experience I would say DO NOT USE Moly in a synchronized tranny. Had a customer about a year ago buy 2 - 55 gallon drums of Texas Refinery Corp. Moly universal gear lubricant for use in his dump truck transmissions and rear axles. Great stuff for those applications and for in Eaton Road Ranger non sychronized transmissions. However, he asked me if I thought it would work in his International 4700 box truck with Spicer 6+ transmission which is synchronized. My answer was a big NO. To make a long story short he did not listen to me and changed the fluid out and installed the Moly gear oil, big mistake. The transmission clashed gears something fierce after that. The only thing I could figure was because it (how should I put this) over lubricated the synchronizers and did not allow them to grip properly when shifting gears. He drained and refilled with the proper 50W synthetic gear oil and the problems went away within 3 or 4 day's. Simply put I would not suggest any Moly, Graphite or Teflon solid film lubricant oil or additive in a synchronized transmission application.

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Thanks for this interesting comment. However using a gearbox additive + proper oil for synchronized gearbox might not be the same as using just the wrong oil. He used a universal gear lubricant formulated with moly but this kind of oil is not supposed to be used in a synchronized gearbox (I mean the oil itself and not necessarily moly here). Redline told me the same when I asked if I could use their Lightweight gearoil (no moly inside) which is a 75W80 GL5, just what my gearbox requires. They actually told me this oil is designed for differential and not for manual gearboxes because it doesn't have the right friction for synchros.

In my situation I think about using a proper gearoil designed for synchronized transmission (so the oil has the correct friction) with a solid MoS2 additive. As far as I understand the MoS2 does not really change the oil, it uses it to reach metalic parts and sticks to them. The difference is that I'm introducing a friction reducer (moly) on gears etc but the oil itself remains more or less "unaffacted" and still has its designed friction characteristics.

This is a pure supposition based on a lack of knowledge but maybe the MoS2 reduces friction when metal-metal contacts occur while proper synchros operation may be controlled by the friction of oil between the two metals......and if this is true then a MoS2 coating of the gears and synchros would not affect synchros operation....... It's hard for me to believe that synchros work really with metal-metal contacts otherwise brass synchronizer rings could not survice more than a couple thousand of km. So the correct friction is achieve by the thin oil film inbetween and if you coat the synchros and gears with MoS2, the thin oil film keeps its right friction (and may be only marginally affected by the MoS2 coating)...just suppositions. In the situation you mention the guy used the wrong oil that had not the correct friction at all so the thin oil film, no matter if moly was there or not, did just not have the proper friction for synchros.

At last as two arguments I would say that first some gearbox oils (for snchronized boxes) are formulated with MoS2 (I think Schaeffer is making some). Second a lot of gearboxes use synchronizer rings coated with Molybdenum (don't know if it's MoS2 though) like Volvo M56 gearboxes for instance.

Would this mean that MoS2 additives may not be as bad as we tend to think??? Please correct if my interpretation of synchros operation is wrong.

 

[kilou]

Just to put it up a little nicer:

----- SUPPOSITIONS -------

The MoS2 coating of synchros and gears only reduces friction when metal-metal should have occured (it acts as a backup for EP additive on gears or as an AW additive on bearings). However it does not significantly affect synchro operation since the latter is controlled by the "shearability" of the oil film between the synchro and the gear. The "shearability" of the oil is a designed feature and it may not be modified (or only marginally) by the MoS2 coating.

Maybe the friction between the MoS2 coating (on synchro) and oil is not reduced and thus it does not affect synchro operation. Only metal-metal friction may be reduced.

------ END OF SUPPOSITION -----------

 

[kilou]

Let's consider one last thing: when the gearbox is new we probably don't need any additive. However overtime with normal wear the synchro and gear surfaces get scored so their friction increases.........maybe MoS2 reduces friction to make it more similar to what it was when the gearbox was brand new and thus allow it to perform better with less noise etc

Should have added it's again another supposition

 

[kilou]

I've contacted Liqui-Moly in Germany, those who manufacturer two gearoil additives with MoS2. I asked how a friction reducer such as moly could smooth out gearshifts since proper synchromesh operation rely on friction. They explained that synchro operation is indeed a limitation in application of friction reducers but when using their additive with the recommended quantity, that was not an issue at all. Sounds realistic.......but then I wonder if the recommended quantity is enough to significantly reduce wear on bearings and gears!