Bill,
  For me the problem was corrosion. The stud had to be cleaned up and
lubricated so the spring force could do its job. Nut also stripped, so
threaded the rusted shaft to 10-32 and used stainless 10-32 nuts. Now
they stay in place.
   Heard click and clack say "to align your mirror to eliminate the
blind spot, lean your head against the side window glass and adjust so
just see the side of the vehicle". I tried it, and it works for me.
    Stan Harrison
    Bethlehem NH