I have a Massey 135. Maybe 1963 model or so with Perkins 3 cyl engine and the 4 speed transmission with high and low range. The problem I'm having is after running through a small ditch while mowing the bush hog kinda dragged the ground when the front of the tractor was coming up throught the swell. At that time the bush hog came up on it's own and the pump was making a noise in the tractor. After a few seconds the pump quits knocking but the lift will not go down. I can fiddle with the lift lever and the lift will slowly go back down. I then pull the lever up a bit and the lift then goes all the way up and the pump knocks again. Happens everytime? I've tried the draft control different positions but no difference. Anyone?