1947 Farmall M Gearbox Disaster

My 1947 Farmall M has developed a gearbox problem. We were working in 2nd gear and all went well until a slight downhill run, when the tractor was not under load. There was a crunching noise as if it was grinding gears. On the flat, the noise disappeared. Pushed in the clutch to stop and over the last few inches it made the noise again. At rest I could not select 1st, 3rd or 5th, but I could select 3rd when driving back to the shed. The tractor is now in the shed awaiting attention. Had anyone had this issue before? I can hear my bank account screaming in terrified anticipation of the upcoming cost! Any advice welcomed.
Thanks,
SadFarmall

Time to pull the top and look inside. You are describing a bearing noise, I think.

Your shift lever is worn on the nend and not putting the rails clean in their position thus letting gears clash as they are not in their normal position, Thats why you can only move the shift lever in some positions. Remove the shift lever and get it built back up like original.

(quoted from post at 08:59:46 03/16/13) Your shift lever is worn on the nend and not putting the rails clean in their position thus letting gears clash as they are not in their normal position, Thats why you can only move the shift lever in some positions. Remove the shift lever and get it built back up like original.

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Good point, if that helps him out it is sure easier than pulling the cover!

I missed the part about not having all position work.

Troubleshooting is difficult when you don't have your hands on the machine.

If that doesent work mite need to remove the top and inspect the rail shifter assy could be rusty ect. Mite also need to check the shift forks for wear and bent. But the shift lever is the first to try and that just mite solve the problem.

One more thing when you remove the pin and get the shift lever out look to see if the rails are all lined up neat and using a long screwdriver move them back and forthe they should snap to their neutral positions after moving. It will be easier if one wheel is jacked up to remove any tension on the gears.

I will add to Gene's idea. Once the shifter is removed, (knockout plugs on lever tower then the pin pushed out. Wiggling and pushing down on lever sometimes helps get a worn pin through) Look in the hole with a bright hand held light(I like an LED Light)You will see a set of three rails with slots in them. The second/third gear, middle, slot will be pushed forward out of alignment. Move this with a little pry bar or big screwdriver back into alignment with the other rails. It may take pushing down the clutch to free tension on the third gear cogs. Don't let it roll out the door!
With the screwdriver/lever, move the rail back and forth between second gear (rearward) and third (forward) if it seems to have nice detent action (like a socket stays on a ratchet with a ball and spring detent) then all is well and building the tip to fit the grooves will fix it (along with a new pin made from a grade 8 bolt shank cut to size)
If no detent action, or very weak, the platform might need to come off to repair the detent balls and springs. I am lead to this statement because the going down hill might have allowed the gear to slide without intention.
It is not a disaster in either case, just a bit of work. Pictures of the tip specs are in the archive. Best of luck and may it have good detent. Jim

Just to add, it should look something like this when you are done. The last one I did was TIG welded so we didn't have to grind it back down after welding.

Thanks everyone! I'm not so scared of looking inside the gearbox now. Hoping it's just a worn shift lever, but if something more, it all sounds fixable.
SadFarmall