Repairs jhon deere 170 5speed shifting problems

[Jd155lt]

hi, this is my second jd 170 the first one i had surged until it was in 3rd gear never found out what was wrong got some wild answers . Now i have one that will not shift the guy took it apart said it might be the cable i know it has a pulley and belt i looked at the parts breakdown on the jd site but it only showed the outside of the transmission can anyone tell me if there is something inside that could be wrong or is there a breakdown of the inside somewhere Thanks DON