Farmall M transmission lock up

Hey guys, I need some expertise. Living in No. Colo. we have pretty much mild winters and I havent experienced this before on my old Faarmall M and I'm only guessing at what is actually wrong. I backed the tactor into my barn last week knowing snow was on the way so I'd like the benefit of keeping it out of the weather, primarily wind and drifts. When I went to drive it out I experienced the issue. I can't start and run although had no issues at all ever in the this manner.With the transmission in nuteral, I found the engine would turn only bit and then be stopped by an internal obstruction. By turning the crankshaft backwards 2-1/2 full turns, I again was met by the same physical stop. Through experimenting I found that with the clutch pedal depressed the engine starts and runs perfect as it normally does but upon slowly engaging the clutch, the engine is unable to get passed the same physical stop. Somewhere in the transmission/differential/PTO drive there is a something wrong. With the tep being around zero degrees overnight I suspected ice formation in the drivetrain somewhere so have drained out the oil in the transmission. It's not entirely warm yet, but I would think that this would lower any ice buidup and allow the machine to move. Not so. What are your thoughts on this. I have had water mized in with oil in other gearboxs preventing motion. I rolled the tractor outside and am awaiting warmth to hep me out but this may not be the answer. I appreciate your thoughts. John

If it has ice in the transmission, draining the oil won't lower the ice buildup as it is already attached to the gears. Need to wrap a tarp around it and use a heater under the tarp to melt the ice.

Being it will roll in neutral, that rules out the differential gears.

If it were frozen I wouldn't think you would see that much rotation then lock, it would be locked completely.

I'm guessing it has to be something in the transmission, something with the meshing of the countershaft and one of the main shaft gears or reverse idler. Possibly a broken tooth or something has fallen into and jamming the gears.

I would take the top off and look inside for the obstruction. Forcing it will likely do more damage.

Thanks to you both for your insight. I've noticed no difference yet from the minimal amount of warming I have experienced so far. The oil that drained out is tan in color which I suspect is mixed oil and water but there was no ice on top of the buckets that sit with the old oil. I must have misled you Steve. The only way I was able to move the tractor was to have my wife hold the clutch pedal down while I pulled it all out of the barn into the sunlight although it's not very warm -- about 40 right now. I've found this morning that the obstruction is in the exact same location when turning the crankshaft. The PTO has a hyd. pump used for the loader so I checked to assure that it is disengaged at this time. It works correctly and is disengaged. It then occurred to me that the belt drive is also driven off the transmission so I assured that it works correctly and is not interferring. Im scared of removing the cover over the transmission--it appears to include a lot more that I am comfortabe with and also can't understand what could have gone wrong when I backed all the way into the barn last week. When I shut her down there was no apparent issue and now, of course when I need it to unload a trailer of hay 3x4s, I can't move it. Maybe I can try lighting a fire underneath to loosen her up, or maybe I should just set the whole thing on fire and go buy a new tractor.

The part about having to hold the pedal down to roll it is what throws me off. You have to have the pedal down even with it in neutral?

It doesn't seem to me like ice could be a problem in the main shaft in the transmission. I suspect you have it locked in two gears,must have happened when you backed it in.

Yeah, I couldn't follow that either.

Especially that the engine will run but lock down when the clutch is engaged.

Ya,I'm still trying to get my head around rolling with the pedal down. If it was locked in two gears,I'm trying to figure how having the clutch disengaged would let it roll. That scenario would only work if the engine was locked up wouldn't it,or am I looking right past something?

I?d say u have some Ice in the rear end (bull gears)!!! Build a fire under it!!!

I don't get the 2 1/2 turn thing, would think if ice it would not turn at all, also if rolls, is not bull gears.

Do you guys know if anything but top shaft turns in neutral?