<font color="blue">Question of my own.....is the physical gear reduction between the IC engine and the hydrostatic pump, or is it between the hydraulic motor and the differential? I can see it working in either place.
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Here's the setup on my B7510HST which has two ranges (Hi, Lo):
Engine-->clutch-->HST transmission-->PTO gear section (front and rear PTO)-->Hi-Lo shift section--->Differential
So, to answer your question, the B7510HST has the physical gear selection between the hydraulic motor and the differential.