I'm a bit confused about what oil type to use on my retrofitted T56 transmission.
Sticker on the trans say "use Dexron II E ATF only".
No problem.

But what about syntetic / semi synthetic / mineral?
Texas Drivetrain, Tremec experts, strongly warns about any synthetic or semi synthetic oils in their Tremec T56.
But is that for my BW T56 from 1994 as well?
I find lots of Dextron 2 ATF but most of them, does not say whenever it's mineral or syntethic based.

 

Found one locally, marked "Dexron 2D ATF Mineral oil"
My transmission sticker says "Dexron 2E ATF"
Is the D vs the E an issue?

 

If that sticker is original to 1994, then it speaks specifically to conditions AS THEY WERE in 1994, not 2024.

We're up to like Dex 6 or something now. I had no idea you could still find anything as obsolete as Dex 2 anywhere. Unless it has a production date on the bottle, it's probably some cheeeeep local producer's Dex 6, relabelled as 2 (which of course it meets all the specs for) for people that think that it's important to use antique fluid in antique assemblies, even though they don't know why, wouldn't recognize the difference, have no clue what's actually different about synth vs "natural", or what's changed in the various iterations of the Dex spec; butt are gullible enough to pay extra for something that eases their misplaced worries.

I own a WW2 military rifle (mine was built in 1943). Its manual has a MIL spec for the grease you're supposed to use in it. That manual was written in about 1936 or 1938. You WOULD NOT BELIEVE how common posts on forums about it are, asking stuff like "I can't find any lube that meets the spec in the manual, anybody know where to get it?" Turns out, if you find a copy of that old spec, all it is, is the length of time in a certain salt-water-spray washout test, the grease has to last. THAT'S ALL. Also turns out, that EVERY SINGLE automotive grease on the market since the 1950s (when all the technology developed during WW2 started to reach consumers), even THE CHEEEEEPEST OF THE CHEEEEEEEEP, exceeds that spec BY FAR. The go-to for that lube today, is Mobil1 synth grease. The red kind that comes in the big tube. 1 tube is enough to lube about 1000 rifles. Somebody tested it against the 1930s MIL spec; turns out, instead of the 30 minutes or something that the spec calls for, they gave up on it after acoupla days, waiting for it to wash out. People STILL ask if it's OK to use synth lube in it, like, is it "compatible"?. It's A FRIGGING PIECE OF METAL for cryin' out loud; what does the metal care how the grease was created, as long as it stays put, lubes the parts, and doesn't gunk up or whatever?

Same deal with the Dex 2 and all that. Never heard of any valid reason - something like, a chemical incompatibility, or that sort of thing - not to use synthetic in anything for any reason beyond CYA. Not sure what they're Cing their A against butt w/e. Can't see why ANY modern ATF, synth OR dinosaur juice, can't be used in it, as well.

GM Synchromesh is kinda the purist's go-to these days for the T-56. Not sure whether it's synthetic or what.

I think my T-56 has Valvoline synth ATF in it. Hard to say whether it works well or anything like that though, it's only been in there since about 2002, so it's a little too soon to draw any conclusions. Butt hay, mine's a 96 I think, so maybe it's different from yours. (NOT)

In case you can't tell, I think WHATEVER ATF you put in it, will be just fine.

 

Thanks for your answer.
I'm aware of improvements and connecting nummeric identification that has developed since 1994.
It's just hard to find any Dexron ATF 3 oils that are mineral based.

 

There's a reason for that.

For all I know (I don't), the newer Dex specs might actually call for synthetic (molecules artificially and consistently built up from methane) ingredients, as opposed to "mineral" (it's just whatever the hell came up out of the ground that day). The molecules themselves are more or less the same, just, "mineral" ones have FAR more inherent variation and impurity in them. Such things move on and leave the old behind.