Graphite-MoS2 additive in manual tranny

[kilou]

Hi,

I'd like to use a manual transmission oil additive to make the gearshift smoother. My transmission use brass synchronizer rings and I'd like to know if there is any problem to use an additive with both graphite and MoS2 with it.

I have no information on the type of MoS2 but I've heard that some may switch to corrosive components when heated too much. Also my transmission oil is a GL5 (which is safe for brass) but I don't know if addibg MoS2 or graphite would be good or not.

I've read the thread about Moly coating the synchronizer rings what may not be good but I know several people who use this graphite-MoS2 additive in their manual gearbox with great results.

Is there any problem to use Graphite-MoS2 additive in manual gearboxes? Why?

 

[mechtech]

So I'm not sure - do you want to know if adding graphite or moly is OK in a trans?

 

[kilou]

Yes that's right but the additive I consider contains both MoS2 and Graphite. My main concern are if MoS2 becomes corrosive overtime and if graphite may make the gearoil too thick.

 

[MolaKule]

Kilou,

Neither powdered Moly NOR Graphite are the proper additives for a manual transmission.

 

[kilou]

quote:

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Originally posted by MolaKule:
Kilou,

Neither powdered Moly NOR Graphite are the proper additives for a manual transmission.

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Which transmission oil additive should I consider then (if any)? I really need an additive since I cannot use another oil because it is very specific for my transmission (as you yet know from the long discussions we had on other threads).

 

[MolaKule]

I thought we had this discussion before.

refresh my memory, what kind of tranny and what fluid do you have in it now?

 

[kilou]

Yes we had a similar discussion a while ago but this was mainly targeted toward silicone and ceramic additives as well as the use of other gear oils.

My transmission requires a 75W80 GL5 lubricant which is safe to brass synchronizer rings. I now use TransElf TRJ 75W80 GL5 as recommended by the manufacturer of my gearbox. My car really requires 75W80 and not 75W90. Some have tried 75W90 on it and the gearshift is awful........and even worse if the 75W90 is full synthetic because it seems they are too slippery. So I really have to stick with my actual oil which has been specifically designed for my gearbox (Elf work in a joint venture with Renault, who built my gearbox.)

So the "only" way I can try to improve gearshift (make them a little smoother and preserve the gearbox which has now 240,000km) is to use a manual transmission oil additive. I've considered different kind of additives and thanks to BITOG forum and you Molakule in particular. I can safely forget the use of:

- Chlorinated products (Prolong, Duralong, Militec etc)
- PTFE additives (Slick50 and other)
- Ceramic additives (Tecflow etc)

So the remaining additives I may consider are mainly based on MoS2. I've also heard "not so good" things about MoS2 coating the synchronizer rings, turning oil black and proved to be very difficult (if not impossible) to remove from the oil pan. However it seems people who use this are rather happy.

The main 2 MoS2 additives I consider are:
- Molyslip 2001G
- Marly GX (MoS2 + graphite in colloidal suspension) http://www.marly.com/en/products/adds/gx.htm

I've contacted Marly technical support and asked if their GX additives containing both MoS2 + graphite would not lower the efficiency of synchronizers which need friction to work properly. They replied that it's true that synchronizers need some friction to work properly but this friction is so low that solid MoS2 particles will not alterate this. MoS2 is mainly designed to lower high load wear on bearings in the gearbox and will not alterate the efficiency of synchronizer rings.

My concernes with MoS2 additives is if they can become corrosive or abbrasive overtime (remember my gearbox uses brass synchronizer rings...) and if it can be mixed safely with a GL5 oil. What would be the real drawbacks of their use in a manual transmission if they seem to be used widely in this application?

 

[MolaKule]

So you're say (just to clarify) the Elf75W80 is about the right viscosity but the friction modifiers aren't quite up to par?

Our SF MTL-P would work very well in your tranny.

Send me a PM.

 

[kilou]

Interesting thing: I've read that at least some Volvo gearboxes (M56) use synchronizer rings coated with Molybdenum!!!!!!! Would this mean that all the bad words against MoS2 additives in synchromesh gearboxes are not really exact? (I understand that Molybdenum is not Molybdenum disulfide but if synchronizer rings are made of Molybdenum, this will reduce friction no?)

 

[John K]

I am not an expert, but I doubt that the syncros were coated with Molybdenum, more likely it is in the alloy mix that they are made of, which would not be the same thing as using a moly coating......

 

[MolaKule]

Most like the moly is part of the set of metals "sintered" into the synchronizers or alloyed into the resulting metal.