FORD 2012 F-550 v.1 - Manual (Page 218)

If the booster seat slides on the vehicle seat, placing a rubberized mesh
sold as shelf or carpet liner under the booster seat may improve this
condition. Do not introduce any item thicker than this under the booster
seat. Check with the booster seat manufacturer’s instructions.
The importance of shoulder belts
Using a booster without a shoulder belt increases the risk of a child’s
head hitting a hard surface in a collision. For this reason, you should
never use a booster seat with a lap belt only. It is generally best to use a
booster seat with lap/shoulder belts in the back seat.
Move a child to a different seating location if the shoulder belt does not
stay positioned on the shoulder during use.
Follow all instructions provided by the manufacturer of the booster seat.
WARNING: Never place, or allow a child to place, the shoulder
belt under a child’s arm or behind the back because it reduces
the protection for the upper part of the body and may increase the risk
of injury or death in a collision.
Child restraint and safety belt maintenance
Inspect the vehicle safety belts and child safety seat systems periodically
to make sure they work properly and are not damaged. Inspect the
vehicle and child seat safety belts to make sure there are no nicks, tears
or cuts. Replace if necessary. All vehicle safety belt assemblies, including
retractors, buckles, front safety belt buckle assemblies, buckle support
assemblies (slide bar-if equipped), shoulder belt height adjusters (if
equipped), shoulder belt guide on seatback (if equipped), child safety
seat LATCH and tether anchors, and attaching hardware, should be
inspected after a collision. Refer to the child restraint manufacturer’s
instructions for additional inspection and maintenance information
specific to the child restraint. Ford Motor Company recommends that all
safety belt assemblies in use in vehicles involved in a collision be
replaced. However, if the collision was minor and an authorized dealer
finds that the belts do not show damage and continue to operate
properly, they do not need to be replaced. Safety belt assemblies not in
use during a collision should also be inspected and replaced if either
damage or improper operation is noted.
Seating and Safety Restraints
218
2012 F-250/350/450/550 (f23)
Owners Guide, 1st Printing
USA (fus)