GMC Sierra Classic 2007 Owner's Manual page 78

5. Pull the rest of the shoulder belt all the way 6. To tighten the belt, push down on the child
out of the retractor to set the lock. restraint, pull the shoulder belt to tighten the
lap belt portion and feed the shoulder belt
back into the retractor. If you are using
a forward-facing child restraint, you may find it
helpful to use your knee to push down on
the child restraint as you tighten the belt. You
should not be able to pull more of the belt
out of the retractor once the lock has been set.
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