SMTA situation

Had an interesting situation today with my SMTA. Drove down the road to the hay field pulling a side rake and stopped for a few
minutes and shut it off. A few minutes later, started her up put it in gear and it won't move! Forward, back, NOTHING! After
pondering this for a few minutes, I stepped on the left brake and it will move, forward and backwards. My first thought was
differential, after towing it home I see the left axle is out maybe a half inch or so. Ant chance the bolt holding the axle to the
bull gear came loose or fell off?

sounds like a good chance

Could be wrong but don't think the bull gear will leave the splines at just 1/2 inch axle out if bolt is out. If the wheel and tire has a lean, could be axle broke. Can jack left side up and remove brake cover to be sure. If turning tire and no turn of pinion shaft something is wrong with axle or bull gear. If pinion turns with tractor in gear your first thought could be correct, differential.

If the big cap screw and flat washer came loose that holds the bull gear on the inner end of the axle, the bull gear probably moved away from the axle and the axle moving out a half inch would probably stop tractor's ability to move unless you step on left brake and force power to right wheel.

There had to have been some unusual noises and vibrations as the bull gear got out of proper mesh with the pinion gear. Our 450 had basically the same rearend, Dad and I both could tell when the differential bearings that supported the pinion shaft got bad, the way the brakes worked was effected and the bull gear whine in road gear was way different. Yeah, Even though I always had the Automatic tractor radio turned WAY Up, I still paid attention to the noises and vibrations the tractor made.

For whatever reason, Neighbor hired me to cultivate 40 acres of corn using a Super M-TA he borrowed from another neighbor, Only took me about half the trip to the field to know the TA and clutch was WAY out of adjustment, but I nursed it along all day and got the 40 acres done. TA had to have been out of adjustment for a long time to be that far out. When I got home I told Dad about the TA. About a day later the neighbor stopped in and wanted Dad or Me to pay for the TA replacement. Yeah, That didn't happen. After that I was Much fussier about who I worked for.

Can I gain at least a good view by removing the PTO unit?

I think you would be wasting your time removing the pto at this point but the bolt in question is accessible through the pto
. I agree with Mr Slater. the inner splines on the bull gear are 2 or 3 inches . the bull gear would have to come off the axle and I think you would have heard a lot of disturbing noises leading up to this problem
I am curious what it turns out to be

(quoted from post at 16:35:38 07/25/18) Had an interesting situation today with my SMTA. Drove down the road to the hay field pulling a side rake and stopped for a few
minutes and shut it off. A few minutes later, started her up put it in gear and it won't move! Forward, back, NOTHING! After
pondering this for a few minutes, I stepped on the left brake and it will move, forward and backwards. My first thought was
differential, after towing it home I see the left axle is out maybe a half inch or so. Ant chance the bolt holding the axle to the
bull gear came loose or fell off?

Click to expand...

It sounds to me like your axle broke.