Chevrolet 70 Series 1970, Service Manual

Page: 174 / 841

SECTION 2
FRAME
FRAME 2-1
GENERAL
T his sectio n in clu d es general in stru ction s for
checking fram e alignm ent and recom m endations
fo r fram e repair and rein forcem en t. It m ust be
pointed out that the inform ation is provided to a s ­
s i s t in the repair or rein forcem en t of fr a m e s, u s ­
ing the m ost d esira b le p r a c tic e s. T his sectio n w as
prepared to aid com petent person n el in the repair
or rein forcem en t of fr a m e s.
Channel-type fra m e (fig. 1) construction with
riv eted c r o ssm e m b e r s is used on a ll m od els.
F ram e sid e r a ils a re u su ally of S.A .E . 1023 s te e l.
On so m e v e h ic le s, sp e c ia l h ea t-trea ted or S.A .E .
950 h i-te n s ile s t e e l sid e r a ils may be used .
In the event the v eh icle is damaged in a c o l­
lis io n , carefu lly check for proper fram e alignm ent
in addition to ste e r in g geom etry and axle alignm ent.
FRAME ALIGNMENT CHECK
The m ost convenient way to ch eck fra m e align ­
m ent, p articu larly when the cab or body is on the
c h a s s is , is to s e le c t variou s corresponding points
of m easurem ent on the outside of each sid e ra il
and then, by u se of a plumb bob, tra n sfer th ese
points to a layout on a le v e l flo o r. (NOTE: Flange
width may vary - 3 /1 6 " .) The selectio n of th ese
p oints i s an arbitrary m atter; how ever, it is an
im portant factor to rem em b er that for each point
se le c te d on the le ft sid e r a il, a corresponding point
m ust be used on the right r a il. The illustration
(fig.
1
) is used m erely to se r v e as a guide in the
se le c tio n of checking points "M."
In order to obtain relia b le r e s u lts , checking
must be done thoroughly and accu rately. After all
corresponding points have been ca refu lly tr a n sfe r ­
red .from the v eh icle fram e to the floor layout,
move the v eh icle away from the layout andproceed
a s d irected in the follow ing step s:
NOTE: Key le tte r s in the follow ing text refer
to fig u re
1
.
1. Check the fra m e width at front and rear
ends using the corresponding m arks on the flo o r.
If widths corresp on d to sp ecifica tio n s (r e fe r to
"Specifications"), draw cen terlin e fu ll length of
v eh icle layout b ise c tin g points indicating front
width (WF) and rea r width (WR). If fram e widths
are not co r r e ct, layout cen terlin e a s d irected in
Step 4.
2. With cen terlin e properly laid out, m easure
the d istan ce perpendicular from the cen terlin e to
corresponding points on each sid e over the entire
length of the c h a s s is . If the fra m e is in proper
alignm ent, m easurem ent should not vary m ore
than an
1
/
8
" at any corresponding point.
3. W here im proper alignm ent is encountered,
the point at which the fram e i s sprung may be lo ­
cated by m easuring p a irs of corresponding diag­
onals m arked "A" or "B." If the length of each pair
of diagonals ("A" or "B") are within 1/8" and the
in tersectio n point of the diagonal p a irs is within
1
/
8
" of the cen terlin e, the portion of the fram e
Figure 1 —Typical Frame Alignment Points
CHEVROLET SERIES 70-90 HEAVY. DUTY TRUCK SHOP MANUAL