Learned that there should be 4 things (in order) mounted to the stepped bolt at the end of the rear brake panel bar. k5 750...
10 mm split washer, 8mm flat washer, nut, cotter pin. If the 10mm split washer is missing, the bar loses some of its rigidness
to freeplay, and can allow the backing plate movement during braking. The force of the wheel being enough to overcome
the axle nut torque as the shoes grab the drum. It can ruin the bushing in the brake backing plate (where the axle passes thru).
Seemed like the axle could slip and or cock sideways either way, depending on when braking or accel. with this condition as well. I fixed mine and learned a bit If my theory is correct
.