Pontiac FIREBIRD 1972 Service Manual page 1162

STEERING 9-9
from being rotated into the "lock" position unless the
transmission shift linkage has been positioned in either the
PARK or REVERSE position. Vehicles with floor
mounted transmission shift linkage incorporate a shifter
tube and lock bracket arrangement in the steering column
which is very similar to that used in the column mounted
shift linkage set-up. Interlock linkage between the trans-
mission linkage and the column shift tube forms a "back-
drive" arrangement to provide the same locking features
for floor mounted as for column mounted transmission
shift linkage.
When rotating the lock cylinder from the "lock" to the
"off' vosition, the rack is moved down the column, releas-
ing thk transmission shift linkage and pulling the lock bolt
from the steering shaft lock plate. This allows the trans-
mission shift linkage and the steering wheel to be moved
freely. Rotating the lock cylinder further, to the "start"
position, causes the rack to move further down the column
to energize the starter through the ignition switch, which
is located on the steering column under the brake pedal
support assembly. An actuator rod outside the column
mast jacket connects the ignition switch contact carrier to
the lower end of the lock rack assembly. Contact carrier
IGNITI
ROD
LOCKED
I
..
\
LOCK POSITION
T R A N S M ~ S I O N SHIFT
L E V E R LOCKED
Fig. 9-4 Locking Mechanism
BEFORE COLLAPSE
I
AFTER COLLAPSE
Fig. 9-5 Energy
-
Absorbing Steering Column Design
movement inside the switch housing establishes the vari-
ous ignition system circuits. When the key is released from
the "start" position, the lock cylinder automatically re-
turns to the "on" position. For vehicles with manual
transmission, a switch activated by the clutch linkage re-
quires that the clutch pedal be fully depressed before the
engine can be started. Operation is similar to that of the
neutral safety switch used on vehicles equipped with auto-
matic transmission.
The energy absorbing steering column is used on all series
cars. This column is designed to compress under impact.
Energy absorbing characteristics are provided by a "tele-
scoping" action in the mast jacket (Fig. 9-5). Thirty-two
balls, embedded in a plastic sleeve, are crimped between
overlapping upper and lower mast jacket sections. As the
column assembly is impacted, the upper mast jacket sec-
tion is compressed over the lower, sliding along the ball
bearings as they deform the tube to achieve a controlled
rate of collapse. The steering shaft and the shifter tube are
held rigid until impact by injected plastic shear pins.
When an automobile is being driven, the forward rnove-
ment of the automobile and the forward movement or the
driver both constitute a form of energy or force. When
ac
automobile is involved in a frontal collision, the primary
force (forward movement of the car) is suddenly halted,
while the secondary force (the driver) continues its for-
ward direction. A severe collision generally involves the.;e
two forces
-
the primary and the secondary forces. The
secondary impact occurs when the driver is thrust forward
onto the steering wheel and column.
The energy absorbing column is designed to absorb these
primary and secondary forces to the extent that the sever-
ity of the secondary impact is reduced. During a collision
the steering column compresses, thereby reducing its tend-
ency to move rearward into the driver's compartment. A
split second later when the driver is thrown forward (the
secondary impact) his energy is also partially absorbed by
the compression characteristics of the column.
The energy absorbing column may be easily disassembled
and reassembled. It is important that only the specified
screws, bolts and nuts be used as designated during reas-
sembly, and that they are tightened to their specified
torque. This precaution will insure the energy absorbing
action of the assembly. Care should be exercised in using