fordnh3930: WELCOME ABOARD to you. There are other young lads your age on this forum who take an active part so don't be shy. It's a good place to learn about tractors and implements,...(and any other topic you can think of). Tractor related folk all over the world book in here on a regular basis.
The double-clutching method is the best way for you to learn how to shift your "particular" tractor tranny. As someone mentioned, they are all different and it is a matter of learning the idiosyncracies of yours. (I mean the little freaky things that yours needs to shift smoothly).
Its going to take lots of experimenting and practice, so just keep in mind that those gears,..WILL NOT...be "forced" together. If you try shifting and they start to clash,..let it go, don't try to force it as you will just start chipping the edges off the gear teeth,.. and you DON"T want to do that!
Synchro rings would slow the gears till they slid together,...but you don't have 'em so you'll just do damage forcing them.
Practice on level ground, if it doesn't go in, abort and start over. Remember also that it doesn't take much to burn out a clutch, so don't ride it,...get your foot off the clutch as soon as possible. Either all the way on or all the way off,...but don't ride it!
You are young with time to practice, experiment and learn the best way. In "time", you may get to where you can "feel" your gears in conjunction with your engine speed,.....and can smoothly slide it out of one gear and into the next withOUT using the clutch at all. Just knowing how much to feather your engine speed (during the double-clutching sequence) to line up the gears in the box as you both gear up and gear on down again is what it takes and that is where "careful" experimentation,...patience ....and "a whole lotta practice" comes in! But I promise you it will put a proud grin on your face when those gears start "slipping" in and out with just a light pull or push of your hand,.....(with or without the clutch)!!!
NEW :...Reading this over a couple days later, I realize that is an awful lot to give you in one shot, so just take your time and don't be discouraged,..."PROPER"-Practice-Makes-Perfect) Lots of good luck to you young fella and let us know how you make out with it.
CHEERS!
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