Cadillac 1993 DeVille Owners Literature page 36

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4. Let the belt go back all the way. You should hear a slight clicking
sound. If you don't, the adjustment feature won't set, and you'll have
to start again.
i
5. Now you can add
a small amount of
slack. Lean
forward slightly,
then sit back. If
you've added
more than 1 inch
(25 mm) of slack,
pull the shoulder
belt out as you did
before and start
again.
If you move around in the vehicle enough, or if you pull out the shoulder
belt, the belt will become tight again. If this happens, you can reset it.