This is one of the most common questions for a new Wedge owner to ask: what gear lube do I use in my 5 speed? The answer is pretty well summarized by an Email post to the mailing list by yours truly so I'll reformat and repeat most of it below. In summary, the original factory fill was straight 75W gear oil. BL quickly realized there was a big problem with 75W, especially when cold and promptly sent out a Factory bulletin advising a refill of automatic transmission fluid, an ATF meeting spec M2C 33G. ATF wasn't great either and ever since, 5 speed Wedge owners have been looking for alternatives. The best has turned out to be GM Synchromesh (made by Pennzoil and available as a Pennzoil product at your local AutoZone). Read on.

I've got some specially modified Redline MTL "Lite" gear oil in my TR8 5 speed. Regular old MTL didn't work when cold, in spite of being equivalent to a straight 75W oil. I've had MTL "Lite" in there for about 5+ years with OK but not spectacular performance to report. The Redline guys convinced me that the GM/Pennzoil Synchromesh lube isn't a true GL-4 spec oil (rather it's a mineral oil) and I should use theirs since it's formulated for gearbox use. You old timers may recall that I actually mailed Redline a sample of the GM fluid back when it was fairly new and they analyzed it! Long time ago now... ages ago in fact. Anyway, I found this posting on the web with an Email (from 2002) which confirms some of Redline's claims about the GM/Pennzoil lube:

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...I actually wrote Pennzoil, just to double check if GM Synchromesh was actually GL-4, and was just not mentioned. This is what I received in response:
--->
Dear David,
Since you did not specify what kind of vehicle you have, I can only tell you that our Synchromesh Fluid is for the following specs only:

  • GM 12345349
  • GM 12345577
  • Chrysler 4874464
    • It does not meet GL4 specs. Only vehicles meeting the aforementioned specs can use Synchromesh Fluid. If you have any other questions or comments, please contact...
    Adolph "D.J." Menuet
    Technical Services Representative
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    The Redline guys convinced me that their stuff would be better for the gearbox and synchros in the long run. Their arguments why are similar to things I find posted on various sites today; here's one from the SVT site:

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    Analysis: Note this [GM 12345349] is a mineral, paraffinic base stock. It has additives and VI improvers, so it is essentially a kind of motor oil adapted for tranny use - no big deal, Honda used motor oils successfully in its trannies for years. However, it does not have the advanced stock of the best ATF's, including the Dexron III/Mercon V, which are essentially Group 3 synlubes. Nor does it have the benefits of a Group IV lubricant such as a PAO (Amsoil ATF), di-basic ester (Neo), or Group V polyol ester (Red Line).
    *****

    So, as you've already read, years ago I swapped out the GM Synchromesh (which worked well) and put in the RedLine MTL Lite. Bottom line after 5+ years driving in all kinds of weather? I don't like it. I'm switching back to GM/Pennzoil Synchromesh (GM Syncromesh 12345349 is actually made by Pennzoil for GM as the note above indicates). No, I'm not going to try any others!

    Jim, 1980 5-speed FI Triumph TR8