In some cases, especially when the tractor has been used extensively with front mounted attachments (blade, snow blower, etc), there is a lot of wear in the front axle pivot joint. As mentioned, the pin is usually the first part to wear. If it is not replaced soon enough, the cast iron axle support casting pivot holes will wear to an oblong shape. There are no replaceable bushings in this casting, so you're left with at least two solutions:
- line reaming the support casing and the axle casting for a larger diameter pivot pin. This requires removing the axle support from the tractor and taking it to a machine shop with the proper equipment.
- line reaming the support casting and the axle casting for replaceable bushings and using a pivot pin of the original diameter.
From experience, make sure the new pivot pin cannot move rearward and contact the mounting surface of the PTO casting. If it does, the movement of the axle will result in the PTO casting breaking.
I have seen the surfaces of the axle and axle support to be worn due to the front-to-back "rocking" motion of the axle. I don't know of a good fix for this, other than to replace those parts.