268 gearbox

Does any one know where I can find a service manual on the gearbox? The baler has been pretty much completely gone through. Only thing I can think of is bearings in the gear box. Mainly looking for the torque specs on the lock nuts for the bearings and shimming.
There is still the problem when you get into very heavy hay it makes the tractor sound like something is wrong. Sometimes like gears are grinding or chirp noise. All seems to come from below my feet on the tractor. I'm using a Ford 4600 gas. Or am I pushing the tractor too hard. Otherwise it bales without any problems.

268 gearbox