You should have a brake pedal! You can also use them as turning brakes as well.
That sounds suspiciously like a hydrostatic transmission. But then, I'm not familiar with the drive systems in larger tractors. If it is, the pedals control the power to the rear wheels and you operate it like an automatic transmission. To go fast, press the pedal down hard, to slow down ease off the pressure on the pedal. Ease off too much and the wheels will stop dead, no matter how fast you're going! Hydro tractors use brakes for turning and parking only. The hydro supplies the braking force when in motion simply by easing off the pedal and reducing the hydraulic flow from the pump section to the motor section of the transmission, if that is what is in the tractor.
Thanks Bob, appreciate your input and form what I'm finding out it's certainly sounding like the way you describe it is what happens. Sounds like a real early form of hydrostatic transmission. I feel more confident about the 1st use of it tomorrow when I back it off the truck and of course that's when all will be revealed and confirmed. I'll post another short advice after learning how it operates in case there's any other subscribers interested, thanks again.