3688 shifting problems

[cornie81]

im no stranger to mechanics and tractors ive been fixing them for decades but i have a weird issue with my 3688 which i can figure out

id say the harvester has a mind of its own and chooses when not to let me put into low or high and its becoming a problem

what should i look at and any potential fixes?

 

[blacktop_j]

if you have been fixing them for decades then i don't think i can be of much help, you clearly have more experience,i know tractor getting stuck in high is something i have seen quite often, i suggest you find someone equally as versed just to get a new perspective may be you're missing something.