We have a New Holland 3630 tractor with the basics. Lately we’ve been having trouble shifting gears. Either you get stuck in reverse or you get stuck in first or second and can’t back up and half the time we can’t use third. A mechanic told us to remove the cover and realign the gears. We do it and it works for a while and then we have to do it again. I think it may need the roll pin replacement but I’m not sure that’s the problem.
With the top cover removed, check your shift lever for any excessive wear as well as the shift forks going to the transmission. Also take a look at the shift collars for your gears to see if any of the teeth are worn in a bullet shape and if any of that is noticeable on the speed gears as well. All of these conditions could potentially cause shifting problems like the one you’re experiencing, as well as a potential out-of-gear slip symptom if they were excessively worn. Check for signs of metal in the drain oil and drain plug that would further confirm an internal problem that would require disassembly of the transmission for further inspection for repair or rebuild. I would also check that the clutch is properly adjusted and there are no signs of slipping.