I have an 87 case 580k and rebuilt the transaxle about 2 years ago. Everything went well except since then I still have a problem with 1st gear popping out under load. Driving around its fine but if I drive into a pile it pops out. If I bungie it forward its fine. When I rebuild the transaxle I replaced 1st, 2nd gear, sliding gear, shifting forks and all bearings and races. 1st gear never seems to 'click' in like the other gears. I never messed with the detent ball and spring. Wondering if this could be causing the problem or if I missed something when rebuilding.
Hey teberhard, the detent is certainly the first place to look. They are not easy to deal with, you may have a broken spring, or worn selector rail. In saying that, I would think that 2nd gear would not be "clicking in" also. Something else that can cause it, is excessive end float in the mainshaft or pinion shaft. If you pull the top cover to check the detent, check the shafts also.
Can there be end float if I replaced all the bearings and races or is there something else that can cause that. The only thing I saw about adjustment in the manual was the gear spacing. If I remember correctly it was with 3rd or 4th gear.
Usually they go back together pretty close to how they come apart, but they often need a little tweek here & there - if they were done right last time...... Also a problem I have seen many times, with assembly of these transaxles if the bearings are not seated properly when fitted, they may move a little when they settle during first use of the machine, creating too much shaft movement. Mainshaft endfloat (I usually adjust close to zero) is adjusted with some thin shims which are between front cover & front bearing cup. Pinion shaft uses different sized spacers between front bearing cone & 4th gear. When the pinion nut is done up tight & the correct turning force for the shaft is attained - there should be a couple of thou clearance between the gears. The shafts may not even be your problem, :beatsme check detent first & at least you have something else to look at as a possible cause.