More pieces to the Synchomesh puzzle
In trying to learn more about the mysteries of (Synchromesh) 'SM' I've found there are two(2) current GM part#s that I think apply to SM lubes:
1) GM 12346190 'Manual Transmission Fluid' ~$20/qt
2) GM 12345349 'Manual Transmission Fluid' ~$9/qt
Why the price difference?
Is either or both a so-called SM?
I 'think' they are both SM's but one is the synthetic version and the other is either conventional or blended. If so I think it's pretty obvious which is which.
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In the general aftermarket there are SM fluids available from Pennzoil, Quakerstate, Texaco. They are absolutely dead on identical to each other so as to suggest it's the same product. I wonder if these are the same as the '349' fluid from GM?
code:
Brand Product @40C @100C VI Pour C Flash C
Pennz Synchromesh Fluid 41.6 9.1 208 -50 385
Texaco MTX Synchromesh Fluid 41.6 9.1 208 -50 385
Quaker Synchromesh Fluid 41.6 9.1 208 -50 385
At any rate they seem to suggest they are a bit heavier than a typical ATF but lighter than RLs synthetic high temp ATF or MTL.
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I have heard various rumours and mention of a Castrol Syntorq LT product that is supposed to be the GM synthetic SM '190' product OEMer. However this product is simply not available to the public except possibly in bulk containers from what I can tell. I have found it posted on at least two distributors websites specifically as a
"75W-85" gear oil
code:
Brand Product @40C @100C VI Pour C Flash C
Castrol Syntorq LT 72.7 12.2 165 -56 224
Fairly close though a little lighter than a synthetic 75W90 GL4 would be my guess. The 75W-85 mentioned by distributors doesn't seem that far off. But those numbers don't look at all like the "SM" #s above now do they!?!?
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These specs are quite different from the ones grouped above. I have NO specs whatsoever from the actual GM fluids themselves to compare to nor do I expect any though I have made repeated requests of GM. Perhaps someone has some part #s and/or product specs from Chrysler to offer?
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Finally I read or heard somewhere that SM and specifically Castrol Syntorq developed Chrysler and Castrol together to replace ATFs for the T-56 Viper tranny. Someone emailed me offline a quote from another site: "Due to the 90-degree V-10's uneven firing cycle, it set up harmonics at idle that caused "neutral gear rattle" with the car idling in neutral, which generated lots of customer complaints. The C5 [Corvette] also uses a version of the T-56 (although the Viper-specific unit uses bigger bearings and different metallurgy for the gears), so GM picked up the Chrysler/Castrol-developed lube and gave it their own name." It's an interesting quote. It seems to corroborate what I've heard elsewhere regarding SM and Syntorq and GM/Chrysler.
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THought I'd piece together everything I've been able to gather and throw it out in the hopes of encouraging others to come forward with what shreds of info they have gleaned. I see SM mentioned in certain car circles as being good for 'other' transmissions though this is by no means a universal claim. What's particularly puzzing is exactly what is meant by the term 'SM'. I have found at least 2 GM part#s for what may be SM. I have also found links to possibly two radically different fluids from two different sources at least 1 of which blatantly claims to be a 'SM' fluid.
On another note this is likely another by-product of APIs continued sitting around and doing nothing about the lack of a fully validated manual transmission lubricant spec. Hello API! Are you listening?!
