Will it go into 5th and 6th gears? They are the same gears, just in a different range. 

My guess is that someone has taken the shift lever out, and got it back in the wrong slot. There are a few it can drop into, but only one is right. Put the tractor in neutral, and then remove the shift lever. Shine a light down in there, and you should be able to see the interlock, and that the notches line up. The center rail is your hi-lo range, and the sides do the gears. Make sure they are lined up. See the picture below from my 2050, in that one they are lined up for the low range (1, 2, 4, and R1.) and the cover was off for that picture.

If that isn't the problem, then you are going to want to pull the transmission cover off and see what's wrong, because it has to be on the inside. Could be a bent or loose shifting fork, sticking rail(s) or a gear seized to a shaft. If it works ok in 5 and 6, then my money is on a misplaced shifter.


On the tires, the standard tire was 18.4-38 rears and 14.9-26 on the front. The thing you have to watch out for when switching tire sizes is that speeds match up front and rear, or you will have trouble. There were other sizes available. So what rear you switch to will possibly change the front size as well. It depends on the rolling diameter of the tires, and which gear ratio was used in the front axle. Easiest way to measure the rolling diameter of your current tire is to mark it heavily with chalk, then drive ahead and measure the distances between the 2 chalk lines. If you don't want to switch the front, look for a new rear tire that has a similar rolling diameter.