Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Welcome to JUST ANSWER small engines, let me try to help you !! I don't know it all, but maybe together we can get you a satisfactory answer!
What part did you replace? The hydrostat or the gear box? Hydrostat has to drive the gearbox, if it does, gear box may have broken gear.??
Is the hydrostat driving the gearbox?
Is the connection between hydrostat and gearbox good?
How did it connect? Keyway or spline?
Got to love it! Looks to me you need to slip the gear box off ans check the hydrostat.