The rear spindle nut needs to be very tight, in the order of 160lbft tight. It's only the friction that the tension in the spindle creates that stops the spindle moving out of alignment. The adjuster screws and bars play no meaningful part in holding things in place against the forces generated between the drive belt and the tyre contact point; they bend really easily.if the nut isn't tight enough.
I'll stand by my description of the correct way to do up the spindle as "effing tight, then tighten till you can get the pin through the castellations."
The older you get the longer the wrench handle you will need. I am just about hanging off the wrench to loosen/tighten that castellated nut from below with mog on lift.
