Most recommend Case IH or Cub Cadet Hy-Tran fluid, but this is a commonly debated topic, as most other trans/hydraulic fluid will also work without issue. Whether be TSC "Traveller" brand, The "Harvest King" brand that my 107 runs with, or even the John Deere version of the fluid. They will all work and shouldn't cause any issue with the transmission, especially since you've got a gear drive. Hydros are a bit different, really all you need the fluid to do is stick to the gears and bearings, and lubricate them. Just about all brands of trans/hydro fluid will get that done no problem. (Please don't start a debate I'm just trying to state everything I've heard
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The transmission design is relatively simple, with 2 gear sets to shift, allowing for 3 forward speeds plus an idler gear for 1 reverse speed. Realistically the stuck transmission shouldn't have to do with these gears themselves, unless it happens to be stuck in a gear. To check that simply pull the top cover on the transmission where the shift lever is, look at the shifter forks (there's 2, one on each side) and make sure they both are in the center (neutral). If one isn't in neutral attempt to move it out of gear by hand.
Now it is possible that one of the 2 tabs that she shift lever slides into in order to shift the gears has broken off completely, or bent far out. They are particular weak points in the transmission, and mainly break when someone tries to force the tractor into a gear. They can be welded to add strength and keep them from bending/breaking in the future. The pic below is the shift fork area beneath the top cover. I have labeled front/rear and the tabs that I am talking about. It also shows where they should be in order to be in neutral.
normal_trans (1).jpg
If both are in neutral and everything still will not turn freely, you could be dealing with a stuck bearing, which may require tearing further into the transmission to remove and replace it. Hopefully not, though!
Here's the manual for the 70/100 tractors from the tech section:
https://s3.us-east-2.amazonaws.com/c...ervice+Man.pdf
(sorry if I'm a bit hard to follow, it's hard to explain what you know if you don't know the exact names of the parts
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