John Deere JX75 clicking transmission pushing in forward

[Westcoastmcgyver]

new to me 9 year old JX75, re and re the pinions (smooth work as should) but when i push the mower forward (without tranny engaged) I get a click/stall it seems at the same point with every wheel rotation. I've checked the spring attached to the clutch and the plastic clutch lever seems to move fine. I'm thinking it is internal but reluctant to open up the transmission. Looking for a manula/schematic of the transmission or ideas. Feels like a gear is not completely disengaged. When transmission is engaged running it works perfectly. Ideas? thanks