Chevrolet 70 1969 Series, Shop Manual

Page: 110 / 913

SECTION 2
FRAME
GENERAL
This section includes general instructions for
checking frame alignment and recommendations
for frame repair and reinforcement. It must be
pointed out that the information is provided to as­
sist in the repair or reinforcement of frames, us­
ing the most desirable practices. This section was
prepared to aid competent personnel in the repair
or reinforcement of frames.
Channel type frame (fig. 1) construction with
riveted crossmembers is used on all models.
Frame side rails are usually of S .A .E . 1023 steel.
On some vehicles, special heat-treated or S .A .E .
950 hi-tensile steel side rails may be used.
In the event the vehicle is damaged in a colli­
sion, carefully check for proper frame alignment
in addition to steering geometry and axle alignment.
FRAME ALIGNMENT CHECK
The most convenient way to check frame align­
ment, particularly when the cab or body is on the
chassis, is to select various corresponding points
of measurement on the outside of each side rail
and then, by use of a plumb bob, transfer these
points to a layout on a level floor. (N O T E : Flange
width may vary - 3 /1 6".) The selection of these
points is an arbitrary matter; however, it is an
important factor to remember that for each point
selected on the left side rail, a corresponding point
must be used on the right rail. The illustration
(fig. 1) is used merely to serve as a guide in the
selection of checking points " M . "
In order to obtain reliable results, checking
must be done thoroughly and accurately. After all
corresponding points have been carefully transfer­
red from the vehicle frame to the floor layout,
move the vehicle away from the layout andproceed
as directed in the following steps:
N O T E : Key letters in the following text refer
to figure 1.
1. Check the frame width at front and rear
ends using the corresponding marks on the floor.
If widths correspond to specifications (refer to
"Specifications"), draw centerline full length of
vehicle layout bisecting points indicating front
width (W F) and rear width (W R ). If frame widths
are not correct, layout centerline as directed in
Step 4.
2. With centerline properly laid out, measure
the distance perpendicular from the centerline to
corresponding points on each side over the entire
length of the chassis. If the frame is in proper
alignment, measurement should not vary more
than an 1 /8 " at any corresponding point.
3. Where improper alignment is encountered,
the point at which the frame is sprung may be lo­
cated by measuring pairs of corresponding diag­
onals marked " A " or "B ." If the length of each pair
of diagonals ( " A " or "B") are within 1 /8 " and the
intersection point of the diagonal pairs is within
1 /8 " of the centerline, the portion of the frame
Figure 1 — Typical Frame Alignm ent Points
CHEVROLET SERIES 7 0 -8 0 H EAVY DUTY TRUCK SH O P M A N U A L