1936 is correct. It was a mid-year change. There was also a cab change at the same time. The early '36 with mechanical brakes used the same cab as the '35, and is referred to as the "High Cab". the hydraulic brake trucks had a lower roofline cab that I think was used to '38, they are the "Low Cab" models.
Side note; Ford did not get hydraulic brakes until 1940, Henry was very stubborn about change, and he didn't feel that hydraulic brakes were any better than mechanical.
