Buick LeSabre 1965 Service Manual page 439

7 - 1 2 TROUBLE DIAGNOSIS
CHASSIS SUSPENSION
(3) Front tires of unequal diam-
eter due to wear.
(4) Incorrect or uneven caster or
bent steering knuckle (par. 7-18).
c. Car Wander or Lack of
Steering Stability
(1) Heavy cross wind.
(2) Type of road surface.
(3) Low or uneven tire pressure
(par. 1-2).
(4) Wheels toe out in straight
ahead position (par. 7-18).
(5) Incorrect or uneven caster or
camber (par. 7-18).
(6) Steering gear or tire rods ad-
justed too loose or worn, or ad-
justed too tight (par. 8-4).
(7) No lubrication in ball joints
or upper ball joint worn (par. 7-5).
d. Road Shocks Transmitted
to Steering Wheel
(1) High tire pressure (par. 1-2).
(2) Wrong type or size of tires
used (par. 7-1).
(3) Uneven tire wear (especially
shoulder or cornering wear)
(par. 7-4).
(4) Steering g e a r or tie rods
loosely adjusted. Broken tie rod
spring (par. 8-4).
(5) Shock absorbers inoperative
or leaking (par. 7-5). Wrong
valving (par. 7-1).
(6) Steering knuckle upper ball
joint worn (par. 7-11).
e. Front Wheel Shimmy
(low speed)
Low speed shimmy is a rapid
series of oscillations of the front
wheel and tire assembly as the
wheels attempt to point alternate-
ly to the right and left. This
movement is often transmitted
through the steering linkage to
the steering gear. Low speed
shimmy usually occurs below
30 MPH.
(1) Uneven or low tire pressure,
or highly worn tires (par. 1-2).
(2) One or both wheel and tire
a s s e m b l i e s out of balance
(par. 7-8).
(3) Front wheel bearings loose
or worn (par. 7-10).
(4) Incorrect alignment of front
wheels (par. 7-18).
(5) Steering knuckle upper ball
joint worn (par. 7-U).
(6) Steering gear or tie rods in-
correctly a d j u s t e d or worn
(par. 8-4).
f. Wheel Tramp, Front or Rear
Wheel tramp, sometimes called
high speed shimmy, is a rapid
up and down movement of a wheel
and tire assembly, as though the
tire was decidedly eccentric. In
severe cases the tire actually
hops clear of the road surface.
Wheel tramp may develop in
either front or rear wheels, and
occurs at speeds above 35 MPH.
(1) Wheel tire or brake drum
out of balance (par. 7-8).
(2) Excessive tire and wheel run-
out (par. 7-7).
(3) Shock absorber inoperative
(par. 7-5).
(4) Items 1, 2 or 3 in combination
with one or more items listed
under Front Wheel Shimmy (sub-
par, e, above).
7-7 CAR ROUGHNESS
OR VIBRATION
a. Various Causes
Car roughness or vibration may
be caused by road surface con-
ditions as some types of road set
up unusual vibrations in cars at
various speeds. Testing the car
on different types of road will
indicate if the road surfaces are
causing the vibration.
Some types of tire treads, tires
with more than four plies of fab-
ric, or tires of greater weight
than those chosen for production
may cause abnormal vibration or
roughness. If car is equipped with
tires other than those which have
b e e n selected for production
equipment (par. 7-1) it is advis-
able to test the car with standard
tire equipment before deciding
that a mechanical condition is the
cause of roughness.
The following procedure should be
used to determine cause of rough-
ness or vibration in car operation
at various speeds, which may be
due to an unbalanced condition of
wheels, tires, brake drums, pro-
peller shaft, or engine.
1. Jack up all wheels, having jack
support rear end of car at center
of rear axle housing.
2. Check runout of front and rear
wheels and tires. Runout should
not exceed specifications shown
in Figure 7-5. See subparagraph
b, below.
3. With transmission in Direct
Drive run engine at various car
speeds to note speeds at which
vibration or roughness occurs.
4. Remove rear wheels and run
engine again at the critical speeds
noted in Step 3. If roughness is
gone the condition is caused by
unbalanced wheel and tire assem-
blies (par. 7-8).
5. If roughness still exists with
rear wheels removed, remove
rear brake drums and repeat the
running test. Elimination of the
roughness indicates out of balance
brake drums (par. 9-12).
6. If roughness still exists with
brake drums removed, run engine
with transmission in Neutral.