After three or four go arounds with AZ Tractor Guy, I put together ratios and speeds for M thru 660. Here are the ratios:
M & SM standard first 44/19 = 2.31 ratio
M & SM low-low first 49/14 = 3.50 ratio SMTA, 400, 450 first 52/21 = 2.47 ratio 560 standard first 54/19 = 2.84 ratio
Percent reduction of M/SM low-low over M/SM standard = 33% slower with LL gears.
Here are the speeds
MV standard first @ rated rpm = 2.00 mph
MV low-low first @ rated rpm = 1.34 mph M & SM standard first @ rated rpm = 2.625 mph M & SM low-low first @ rated rpm = 1.758 mph SMTA first-high range @ rated rpm = 2.0 mph SMTA first-low range @ rated rpm = 1.625 mph SMTA with 560 first gear and low range @ rated rpm = 1.41 mph
Lower speeds on SMTA/400/450 can be achieved with 560 ring and pinion. Not sure if 560 ring and pinion (tranny mainshaft) will fit M/SM.
Even lower speeds can be achieved with 660 planetary hubs. I think the reduction is 25% off of 560 speeds with both running at the same rpm. Data was derived from IH Parts Book TC-46 and Guy Fay's Data Book.
Speed reduction can also be achieved with an aftermarket auxiliary transmission. There were about 20 of these tractors in AZ. One of them sold on eBay two or three years ago. Looks like I didn't save the pictures.
I also think a home-made Hydro-Creeper could be attached to one of the pinion shafts. It would probably be easier to fit to a disc brake tractor. It would have to be a quick disconnect hydraulic motor with alot of displacement.
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