Right now the CNHI parts page is down for updates. Need to know if you have a Farmall row crop or utility model. Do not know how familiar you are with it but a linkage with two rods and a bell crank transfer the shifter motion from the shifter down to the transmission. One for each set of gears on either side of neutral, as in reverse and first. So there is 3 sets. Tightening up the slack in all those joints is what needs done, new pins for all the joints is a start. I will link another parts site that shows the diagram for the Farmall version. Do a web search on this problem a lot of info will come up.