GMC 4000 Series Service Manual page 521

Sec. 10
Page 510
WHEELS A N D TIRES
inspection should be made of the tire showing the
loss and the cause of loss corrected. This method
should definitely establish a "danger signal" on
the condition of the tires. The pressure lo ss check
should be made consistently with the same gauge,
so that any element of inaccuracy in the gauge will
be the same for all tires.
VALVE CORE AN D CAP
The valve core is a spring-loaded check valve
in the valve stem, permitting inflation or deflation
of the tube or tire. This check valve, or core, is
not intended to hold the air during operation. The
valve cap is provided to seal the air in the tube
and tire. When valve cap is tightened down on stem,
the sealing washer inside cap is pressed tightly
against top of stem , preventing air leakage. It is
important, therefore, that valve caps be used at
all tim es.
SELECTION OF TIRES
All tires on an axle should, whenever possible,
be of the same make, since difference in design
and tread in some instances result in unequal tire
rolling radii. When installing tires, all tires on
each axle should have the same outside diameter
within 1/4-inch on tires up to and including size
9.00-20, or within 1/2-inch on sizes 10.00-20. If
tires do not have the same outside diameter (with­
in the above limitations), excessive tread scuffing
and hard steering will result. In highway service,
the sm aller of the two tires on a dual assembly
should be installed on the inside position, provided
its diameter is within the tolerance described
previously.
WHEEL STUDS OR BOLTS
IMPORTANT: If any wheel experiences a
single stud failure caused by a loose-running wheel
all studs should be replaced. A loose running wheel
may cause only one stud to break, but several more
studs may become fatigued to the point of failure,
G M C S E R V I C E M A N U A L
but not actually breaking. Replacing only the one
broken stud and remounting wheel will then set the
stage for a second and possibly more serious fail­
ure. If holes in wheel have become elongated or en­
larged, replace wheel.
tervals to obtain maximum tire life. Refer to figure
6. If there is uneven tread wear on front tires,
rotate tires immediately and check vehicle for
mechanical irregularities. Since there are three
tires on each side of the vehicle, the front tires
should be moved to the rear when 1/5 of the tread
life has been used. When tires are moved to rear,
follow recommendations previously described un­
der "Selection of Tires" in matching them with
other tires.
TO REPAIR TIRE. HAVE REPAIRS MADE BY A
RELIABLE TIRE REPAIR SHOP.
TIRE ROTATION
Tires should be interchanged at regular in­
TIRE MOUNTING
UNLESS EXPERIENCED, DO NOT ATTEMPT
CAUTION
Most truck "rim accidents" are caus­
ed by carelessness, thoughtlessness, or
lack of experience, when inflating the tire
after mounting. Such accidents are always
serious and sometimes fatal. Be on the
safe side - - always follow the precautions
explained following:
On all rims, the lock ring must be fully
seated in the rim gutter before inflating
tire. This is important for the safety of
the person inflating the tire. As a safety
measure, observe the following precau­
tions:
On Budd or disc type wheels, use a
steel bar approximately 1" in diameter
and long enough to extend several inches
over the lock ring at both ends. Bend bar
so it can be inserted through wheel spoke
openings with both ends of bar extending
over the lock ring. Leave bar in place
until tire is fully inflated, examine lock
ring to see that it is fully seated, then re­
move safety bar.
Oncost wheels, wrap tire and rim with
a chain at opposite sides of rim and se­
cure ends of chain. Leave chain loose
enough to permit expansion of tire during
inflation. After inflating, examine lock
ring to see that it is fully seated, then re­
move chain.