Without the metal tag or the decal you're pretty much restricted to spinning the output shaft to determine the OD ratio. Normally, the S10-15 T5's from behind the V6 engines are .72's while those behind the L4's are .86 OD's with the ultra-low 4.03 1st gears.

I've found the easiest/most reliable way to determine the OD ratio on a transmission without the tags is to:

Make a mark the output shaft....say at the 12 O'clock position and also in the same position on the input (front shaft).

Put the transmission into 5th gear.

Slowly rotate the output (rear shaft) 1 full turn while watching the mark on the input shaft.

If the input shaft PASSES the 3/4 (270 degree) position you have a .86 OD. If it doesn't quite turn to the 3/4 position you have a .72 T5. If it's appreciably less than 3/4 you can figure a .63 which is common in the Camaro T5 boxes.

Probably not the most scientific way of checking a box but with no tag and the transmission laying on the ground, it will help ID the OD ratio. None of the casting numbers on the box will identify the specific OD ratio.

As for the fluid used.....the World class with the synthetic composite synchronizers will definitely require automatic transmission fluid or it's equivalent. I've also found many Non-World class (brass synchros) running ATF with no evidence of metal in drained fluid. In addition I've run 80-90 gear oil in my NWC 85 .72 T5 for the past 10K miles with the same lack of metal residue. It had gear oil in it when I purchased it. With our higher average ambient temps it shifts smoothly with NEVER any drag. Royal Purple makes a substitute replacement for the Dextron fluid call "Synchromax" that I'll run in my retro-hot rods brass synchro hybrid T5.

Hope this helps you ID your transmission.

Dave

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