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Suggestions for what the best manual transmission fluid is


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I have my 510 wagon with VG33 engine up and running and using it for errands around town - my project page has pictures. https://ratsun.net/topic/74834-72-510-goon-prova-because-it-will-be-a-test/


What I am curious about is the best transmission fluid to use?


The trans is a 5-speed Z31 transmission: FS5W71C and it works in all gears and shifts. It is a little bit noisy. I have no idea the origin of the trans - it came with the car and was bought a few years before I got the car. Not sure of the miles or history at all.


So I am looking to put the best fluid I can into it to either help renew it or at least keep it from getting ruined. I was thinking about using Amsoil synthetic manual transmission fluid.



What does everyone think? Any better suggestions?



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Synthetic? Sure that will work but on an older transmission it may start leaking from the rear seal by the driveshaft. If it does pull the driveshaft and replace the seal. Two liters will do the job.

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I began using Redline products in my Mitsubishi FWD transmissions years ago.  they offered a 75W85 GL4 (safe for brass synchros) that matched requirements.   with that.


For my older Datsuns (RWD), I have used mostly Valvoline, but I would have to confirm what viscosity.  I will be using a 280ZX trans in my 510 here in the near future, but I have not researched yet what viscosity that requires.  I will probably choose Redline if I find a match.


I wouldn't really worry about synthetic leaks.  This application is not pressurized, and you can certainly change the rear seal relatively easily if there is a problem.

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The GM Delco oil I use is thin! Like noticeably thinner than the 80w90 GL-4 regular dinosaur oil. So I don't know what viscosity it is, doesn't say. As mentioned previously I think all Synthetic gear oil is made by one supplier and brands just add coloring and a name.

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A very long time ago I owned a 1949 Mercury.  The owner's manual specified that for Alaska the manual transmission should be thoroughly cleaned and well lubricated with Kerosene for winter service.  Yes, Kerosens for transmission lube [after all we are talking Alaska].

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18 hours ago, datzenmike said:

Still what did a '49 Merc put through the transmission back then, a little over 100 hp?


Not sure.  It also had an overdrive.  Fun playing with it, 6 forward speeds and 2 reverse !  Not the way it was ntended to be used but a hell of a lot of fun.

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My dad's first car was a 5 year old '51 Chevy. I think the bearings were babbitt and crank oiling was by splash. Good enough for 60-70 HP but would never stand up to six cylinders making twice that 10 years later.  

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