Chevrolet 1977 light duty truck Service Manual page 333

one will be affected. The scraping action against the face
o f the tire causes a small feather edge of rubber to
ap p e a r on one side of the tread and this feather edge is
certain indication o f misalignment.
readjusting toe-in, or rechecking the entire front end
alignm ent if necessary.
Uneven W ear
U neven or spotty wear is due to such irregularities
as unequal caster or camber, bent front suspension parts,
out-of-balance wheels, brake drum s out o f round, brakes
out o f adjustm ent or other mechanical conditions. The
rem edy in each case consists of locating the mechanical
defect and correcting it.
C ornering W ear
W hen a truck makes an extremely fast turn, the
weight is shifted from an even loading on all wheels to
an abn orm al load on the tires on the outside o f the curve
and a very light load on the inside tires, due to
centrifugal force. This unequal loading may have two
unfavorable results.
the rear tire on the inside of the curve may be
First
relieved of so much load that it is no longer geared to
the road and it slips, grinding off the tread on the inside
half o f the tire at an excessive rate. This type of tire
shows much the same appearance of tread w ear as tire
w ear caused by negative camber.
the transfer o f weight may also overload
Second
the outside tires so much that they are laterally distorted
resulting in excessive wear on the outside h alf o f the tire,
producing a type o f wear like that caused by excessive
positive camber.
C o rnerin g wear can be most easily distinguished
from ab no rm al cam ber w ear by the rounding of the
outside shoulder or edge
roughening o f the tread surface which denotes abrasion.
C o rn erin g w ear often produces a fin or raised
portion along the inside edge o f each row in the tread
pattern. In some cases this fin is almost as pronounced as
a toe-in fin, and in others, it tapers into a row o f tread
blocks to such an extent that the tire has a definite "step
w e a r" appearance.
T he only rem edy for cornering wear is proper
instruction o f operators. D riving more slowly on curves
an d turns will avoid g rinding ru b b e r off tires. To offset
norm al cornering w ear as much as possible tires should
be interchanged at regular intervals.
Wheel and Tire Balancing
It is desirable from the standpoints o f tire wear and
vehicle ride and handling ease to m a intain proper
balance o f wheel and tire assemblies on all models. This
may be accomplished by either o f the two types o f
balancing systems in currect use which balance wheels
either on the vehicle or off. The "o n the vehicle" type,
however, is the more desirable in that all rolling
components (brake drums,
The remedy is
o f the tire and by the
bearings, seals, etc.) are
included in the balancing procedure and thereby have
any existing unbalance corrected.
Truck Wheel Balance Weights
All 1977 truck wheels equipped with a tubular side
ring (rolled flange rim) on the outboard side o f the
wheel rims require special design weights to fit. D ynam ic
balancing can be accomplished through use o f these
special balance weights which are designed only for
installations on the outboard side o f these wheels.
Conventional weights fit only the inboard side o f these
wheels.
Static Balance
Static balance (sometimes called still balance) is the
equal distribution o f weight o f the wheel and tire
assembly about the axis o f rotation in such a m anner
that the assembly has no tendency to rotate by itself,
regardless o f its position. For example: A wheel with
chunk o f dirt on the rim will always rotate by itself until
the heavy side is a the bottom. Any wheel with a heavy
side like this is statically out of balance. Static unbalance
o f a wheel causes a hopping or pounding action (up and
down) which frequently leads to wheel "flutter" and
quite often to wheel " tra m p " .
Dynamic Balance
Dynam ic balance (sometimes called running balance
means that the wheel must be in static balance, and also
run smoothly at all speeds.
To insure successful,
following precautions must be observed:
• Wheel and tire must be clean and free from all
foreign matter.
• The tires should
properly mounted with the balance mark on the tire, if
any, lined up with the valve.
• Bent wheels that have runout over 1/16" should
be replaced.
• Inspect tire and wheel assembly to determine if
an eccentric o r out-of-round condition exists. Note that
this condition, if severe, cannot be "balanced out". An
assembly which has an out-of-round condition exceeding
3 /1 6 " on tire sizes through 19.5" is not suitable for use
on the front o f the vehicle. Its use on the rear should be
governed by its general condition and whether the
roundness defect seriously detracts from overall ride
quality.
• W hen balancing wheels and tires, it is recom­
mended that the instructions covering the operation o f
the wheel balancer being used be closely followed.
• W hen balancing truck type nylon tires, tires
must be hot (run for several miles) before raising vehicle
to balance so that flat spot is elimated. A tire which is
flat spotted will be incorrectly balanced.
WHEEL REMO VAL AN D IN S TA LLA TIO N
Jacking Instructions
Place vehicle jack supplied or recom m ended as
follows: To raise a rear wheel, place jack under axle
accurate balancing, the
be in good condition and