Chevrolet 70 1969 Series, Shop Manual

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CHASSIS ELECTRICAL AND INSTRUMENTS 12-9
LIGHTING SYSTEM
Headlights are equipped with “ T-3” Sealed-
Beam units - all other lights are replaceable bulb
type. Refer to “ Specifications” at end of this
section for bulb size and trade number. Head­
lights and parking lights are protected by a 25-
amp. circuit breaker built into the main light
switch.
HEADLIGHTS
All vehicles covered by this manual use the
7-inch single sealed-beam unit type headlights or
dual headlights, using four 5-3/4-inch sealed-beam
units.
H E A D L IG H T B E A M A D J U S T M E N T (FIG. 11)
Both the 5-3/4-inch and 7-inch sealed-beam
units are ''T-3” type units. Each "T-3" sealed-
beam unit lens incorporates three projecting guide
points which are optically ground to provide flat
surfaces at right angles to the light beam. This
design, in addition to providing superior lighting,
permits adjustment of the light beams without the
use of an aiming screen and without requiring a
large work area. Aiming is accomplished with the
use of a "T-3 Safety A im er.” Safety aimer (J-6408)
can be used for adjusting the single 7-inch units.
A later design aimer (J-6663) must be used on the
dual 5-3/4-inch units; an adapter is provided with
this aimer so that it can also be used on the 7 -inch
units. Instructions for using the aimer are sup­
plied by the instrument manufacturer.
Headlight beam adjustment requirements will
vary on different vehicles due to size and distrib­
ution of load, type of standard or optional suspen­
sion, size of tires, tire pressures, and other fac­
tors. Average requirements areforthehighintens-
ity zone of the high beams of inner lights on dual
units to be straight ahead and 2 inches below the
headlight level at 25 feet. Low beam of outer lights
of dual units and all 7-inch units should be adjusted
so the high intensity zone of the light beam is just
to the right of the headlight center and just below
the headlight level at 25 feet. To obtain correct
adjustment, beam adjustment should be made with
the vehicle loaded with the normal average load it
will be carrying during the majority of its operation.
Tires should be uniformly inflated to recommended
pressure when adjusting headlight beams. Beam
adjusting screws are identified in View A, figure
12, for dual units and in figure 13 for single units.
In all cases, it must be remembered that state
or local legislation and specific vehicle conditions
will govern the final aim for the best and safest
lighting. Especially in the case of vehicles carry­
ing widely varying loads during night-time oper­
ation, the final decision as to safe operation must
still be made on the basis of "the most light on the
road with the least annoyance to oncoming traffic."
D U A L S E A L E D B E A M UNIT R E P L A C E M E N T
R E M O V A L (Fig. 12)
1. Using a hooked tool, disengage spring from
headlamp retaining ring as shown in View B.
2. Rotate the sealed beam unit slightly to dis­
engage mounting ring from horizontal and vertical
adjusting screws, then pull the assembly forward
to remove (View B).
3. Pull headlamp wiring connector off back of
sealed beam unit.
4. Remove screws which attach retaining ring
to mounting ring. Separate retaining ring from
mounting ring and remove sealed beam unit and
discard (View D).
IN S T A L L A T IO N (Fig. 12)
N O T E : Sealed-beam unit with number " 1 "
molded on top of lens must be used at inside light
position and unit with number "2 " on lens must be
used at outside position.
VERTICAL CENTERLINE
STRAIGHT AHEAD OF
LAMP CEN TER-
VERTICAL AIM - TOP EDGE OF
HIGH IN TENSITY Z O N E AT (H)
LIMITS H ♦ 2 IN.-
LATERAL AIM - LEFT EDGE
OF HIGH INTENSITY ZON
2 IN . RIGHT O F ( V ) ------
LIMITS V TO 6 IN . RIGHT
HORIZONTAL CENTERLINE
LOCATED* AT LEVEL OF
LAMP CEN TER-
AIM INSPECTION LIM ITS FOR LOW ER BEAM OF:
53/4 in. T y p e
2
Sealed B ea m
7 in. T y p e 2 Sealed B e a m
C autio n—D o not aim
o t
inspect these lamps on the uppeT
beam
VERTICAL CENTERLINE
STRAIGHT AHEAD OF
LAMP CENTER
VERTICAL AIM - HIGH
INTENSITY ZONE
CENTERED 2 IN . BELOW (H)
LIMITS + 2 IN.-
LOCATED AT LI
LAMP CENTER-
LATERAL AIM - HIGH
INTENSITY ZONE
CENTERED O N (V)
LIMITS + 6 IN
AIM INSPECTION LIM ITS FOR U PPER BEAM OF:
5
y4
in. Type 1 Sealed Beam
7 in. Sealed Beam, except Type 2
T-3491
Figure 11 —H eadlight Beam Adjustment (Typical)
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L