GMC 4000 Series Service Manual page 106

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 a s­
sist in the repair or reinforcement of fram es, u s­
ing the most desirable practices. This section was
prepared to aid competent personnel in the repair
or reinforcement of fram es.
Channel-type frame (fig. 1) construction with
riveted crossm em bers is used on all models.
Frame side rails are usually of S.A.E. 1023 steel.
Figure 1 illustrates typical arrangement of frame
mounted suspension and body attaching brackets.
In the event the vehicle is damaged in a col­
lision, carefully check for proper frame alignment
in addition to steering geometry and axle alignment.
FRAME ALIGNM ENT CHECK
The most convenient way tocheckfram e align­
ment, particularly when the cab or body is on the
ch assis, 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. (NOTE: Flange
width may vary - 3 /1 6 M .) 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
W F
G M C S E R V I C E M A N U A L
SECTION 2
f y t i a m
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."
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:
to figure 1.
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 (WF) and rear width (WR). If frame widths
are not correct, layout centerline as directed in
Step 4.
the distance perpendicular from the centerline to
corresponding points on each side over the entire
length of the ch assis. If the frame is in proper
alignment,
than an 1/8" at any corresponding point.
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 Fram e A lig n m e n t Points
e
In order to obtain reliable results, checking
NOTE: Key letters in the following text refer
1. Check the frame width at front and rear
2. With centerline properly laid out, measure
measurement should not vary more
3. Where improper alignment is encountered,
Sec. 2
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T-1844