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(213)
CHASSIS SUSPENSION
TROUBLE DIAGNOSIS
6-15
d. Road Shocks Transmitted to Steering
Wheel
(1)
Low or high tire pressure (par. 6-8).
(2) Wrong type or size of tires used (par.
6-7).
.
(3) Steering gear or tie rods incorrectly ad-
justed. Broken tie rod spring (par. 7-4).
(4) Shock absorbers inoperative or leaking
(par. 6-10). Wrong valving (par. 6-1).
(5) Improper caster or bent steering knuckle
(par. 6-30).
(6) Steering knuckle bushings or king pins
worn (par. 6-15').
e. Front Wheel Shimmy (low speed)
Low speed shimmy is a rapid series of oscil-
lations of the front wheel and tire assembly as
the wheels attempt to point alternately to the
right and left. This movement is often trans-
mitted through the steering linkage to the
steering gear. Low speed shimmy usually oc-
curs below 30 MPH.
(1)
Uneven or low tire pressure (par. 6-8).
(2) One or both wheel and tire assemblies
out of balance (par. 6-28).
(3) Front wheel bearings loose or worn
(par. 6-14).
(4) Incorrect caster, camber, or toe of front
wheels (par. 6-30).
(5) Steering knuckle bushings or king pins
worn (par. 6-15).
(6) Steering gear or tie rods incorrectly ad-
justed or worn (par. 7-4).
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 bal-
ance
(par.
6-28).
(2) Shock absorber inoperative (par. 6-10).
(3) Item
1 or 2 in combination with one or
more items listed under Front Wheel Shimmy
~
(subpar.
e, above).
6-12 CAR ROUGHNESS OR VIBRATION
Car roughness or vibration may be caused
by road surface conditions as some types of
road set up unusual vibrations in cars at vari-
ous speeds. Testing the car on a different type
of road will show whether the road is causing
the vibration.
Some types of tire treads, as well as tires
having more than four plies of fabric may
cause abnormal vibration or
roughness.
If car
is equipped with tires other than those which
have been selected for production equipment
(par. 6-7) it is advisable 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 roughness or vibration in
car operation at various speeds, which may be
due to an unbalanced condition of wheels, tires,
brake drums, propeller 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
lis"
at side
of tire.
3. With transmission in third speed, run en-
gine
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 rough-
ness is gone the condition is caused by unbal-
anced wheel and tire assemblies (par. 6-28).
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.
8-17) .
6. If roughness still exists with brake drums
removed, run engine with transmission in neu-
tral. Elimination of the roughness indicates
that propeller shaft is out of
balance.
Continued
roughness with engine running al
on e
indicates
an out of balance con dition of engine.
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