How does a 2-stage hydraulic pump work?

[Redneck in training]

The real solution to variable speed hydraulic transmission is variable delivery pump or dual variable delivery pump one driving left side motors and the second driving right side motors. Look how skid steers or ZTRs are designed.

 

[J_J]

How about something like this.

Surplus Center - ZTR LEFT/RIGHT TRANSAXLE ASSEMBLY

Surplus Center - ZTR LH/RH HYDRO-GEAR ZT-220O EZT TRANSAXLE ASSY

Perhaps something like this and use brakes on each side to steer.

http://www.surpluscenter.com/item.asp?item=13-1474&catname=powerTrans