MoS2 and brass corosivity

[kilou]

OK always the same topic on MoS2 but I've never been able to come to a nice conclusion so I'd like to narrow it down a bit further.

There is a huge controverse on the benefits/drawbacks of MoS2 additive in a manual transmission (synchronized). I don't want to go into the topic of performance of synchronization with antifriction additives as this had been debated already. Here I'd only like to get evidence of potential corrosivity problems of MoS2 on brass (mainly used in synchronizer rings in manual gearboxes). So my questions are:

- is this true that over time MoS2 will degrade into sulphuric acid if supplemented in a gearoil?
- Is it true that MoS2 is especially corrosive for brass synchros?
- If the above is true, then does it mean that the use of any MoS2 (additive or not) is not acceptable in a manual gearbox using brass synchros? If not, what would make the use of MoS2 acceptable?

I'm especially targeting this debate around Lubro Moly MoS2 Gearoil treatment additive (20g tube) that is supposed to reduce wear of the box. I'm using it right now, have worked great over the last 50'000km but this doesn't mean there is no corrosion occuring....

Thanks for your comments!

 

[moribundman]

I don't know about issues with MoS2 regarding corrosion of brass, but the corrosion issues that GL5 fluids may cause in some transmissions appear to be directly related to high operating temperatures. As long as temperatures remain low, no (significant) corrosion occurs.

 

[kilou]

Thanks for your input moribundman. I've heard that MoS2 especially in presence of moisture in the gearbox would degrade and form an acid that was highly corrosive (probably due to the sulphur content). Since MoS2 coats the synchros it would basically corrode the brass below and damage would become obvious after removing the MoS2 layer. This is what I heard but I'm happy to read that no obvious corrosion is to be feared with MoS2 and brass

Now on the GL5 (I also use a GL5 in my gearbox with brass synchros, as recommended by the manufacturer). It seems there are specific EP additive packs that would achieve a GL5 protection without being corrosive to brass. Many of these oils are marketed as GL4/5 or GL4+, stating that they achieve a level GL5 but can also be used in a transmission calling for GL4. Also some of these oils specifically mention that they are safe for brass and yellow metals (such as Texaco MultiGear RN Premium, TransElf NFJ etc). Do you have any opinion on these kind of EP additive packs? Are they not available in the US? At least Texaco mentions its oil use a specific formulation of non-borate additive.....don't know if this would be the reason for it to be non corrosive???

Now you understand my worries: I use a GL5 oil supplemented with an MoS2 additive in a manual tranny with brass synchros........am I calling for breakdown?

 

[Quest]

LOL! your problem is seemingly exaggerated by the general public.

My good ole faithful 323 (B6 block) with MT 5-spd called for GL3 75W90 and over the years, I've used MoS2 (in colloidal suspension, Molyslip made in Canada)mixed in GL-3 semi-syn (MotorMeister semi-syn in 1L silver bottle), to full syn GL-5 Q-state or GL-5 Syntec 75W90.

Although I may not use my ole faithful for towing (thus lower operating temp), that doesn't mean that I've never loaded my car on extended trip to yellowstone (wyoming) and back in a 3K plus run with 4 occupants and photography gears in the trunk. Been on all over the place with this mixture and never had any corrosions or synchro slippage/notchy problems (took the gearbox bellhousing off once to inspect the gears based on sheer curiosity, no fault found on everything...) Also used AutoRx to rid of those seemingly grotesque gray film after running MoS2 with gear oil for so long and once finished with the process and refilled with straight 75W90 full-syn Syntec GL-5, it ran like a charm even @ 186,000kms before I sold it.

Bottomline: you worry too much. When in doubt, don't use additives and just resort to using proper viscosity and grade of gear oil and you'll be home free.

Q.

with my 07 fit, I'm running straight factory OE Honda MTF-II (Idemitsu semi-syn) and never been more happier, even w/o any unneeded additives such as MoS2.

 

[moribundman]

Originally Posted By: Quest
When in doubt, don't use additives and just resort to using proper viscosity and grade of gear oil


I will second that.