HRD536 HX 4 wheel hydrostatic box issue

[Swissqp]

Hello Mick and all,
Weird one for you. Belt driven hydrostatic box on a HRD536 HX....wont roll backwards. The gears ⚙️ on each wheel are correctly orientated. shaft won't turn backwards unless the mower is running and the belt is turning. Dismantled off the mower and still shaft won't reverse direction. checked hydrostatic fluid level which is good. No air in system. Any thoughts? Thanks, Tim

[Mick]

Hi Tim.

I'm assuming the control arm on the gearbox is moving freely on the gearbox, and the return spring is pushing it all the way back. That control arm shaft has been known to seize up or go very stiff.

That's really the only thing that would cause it, unless there's a problem inside the box. Has it got the correct oil in it, and the correct amount?  Also make sure the control arm hasn't got excessive play on the shaft or it might be hitting its stop tab before releasing.