Thanks Allen.
There are several types of Sherman auxiliary transmissions.
Plus a few other brands that were similar and some different.
The most common Sherman is probably the Step-Up transmission.
It is basically a Hi-Lo range added in front of the original trans.
On an 8N, that will give you 8 forward speeds and 2 reverse
speeds. The normal range and a range that is faster than that.
(like an 8N reverse isn't fast enough already?)
On a 9N/2N with the three speed trans, 6 forward, 2 reverse.
Sticking strictly to the Shermans, there was also a Step-down.
This is probably one of the more rare Shermans, step down only.
On an 8N, again, 8 forward speeds and two reverses, but the
other speeds are slower ground speeds than the original.
The Sherman combination in this tractor has both step-up and
step-down plus the original direct drive gearing giving it twelve
forward speeds and three reverse speeds.
As with any auxiliary transmission placed in front of the original,
it also changes the PTO speed. So having a Sherman combo or
step down doesn't really make it much more helpful for, say,
running a rototiller but you have way more options for ground speed.
And I didn't even touch on the Sherman reverser, the Everett
trencher or the Howards etc.
Here's a picture of a Hupp auxiliary I had. It was also a step-up.
Essentially the same as a Sherman step up, but with the handle
on the opposite side. This particular transmission had, at one
time or another, had both a Hupp and a Sherman installed based
on the holes cut into the sides. At different times, of course.