Chevrolet 70 1969 Series, Shop Manual

Page: 111 / 913

FRAME 2-2
included between the points of measurement may
be considered to be in proper alignment. Variation
of more than a 1 /8 ” indicates misalignment.
4. If the frame centerline cannot be determin­
ed by method indicated in Step 1, the centerline
may be established by drawing a line through the
intersection points of equal pairs of diagonals or
from the intersection of equal diagonals through
the midpoint of either correctly established front
or rear frame widths. This method is usually re­
quired when front or rear end damage is incurred
as the result of a collision.
5. After it has been determined that theframe
is properly aligned, axle alignment with respect to
the frame can be checked as directed below: (See
fig. 1.)
a. Front axle alignment with respect to the
frame is correct if " F R ” equals " F L ” and " D R "
equals " D L . " This can be concluded if both front
and rear frame ends have been established as
properly aligned (Step 3).
b. Rear axle alignment with respect to the
frame is correct if ” E R " equals " E L " and " G R "
equals " G L ." N O T E : Alignment may appear to be
off if rear ends of frame rails are not cut-off
evenly when reducing cab to end of frame (CE) for
specific operations.
Straightening Frames
The practice of straightening frames should
not be attempted by inexperienced personnel, as
more damage can result from improper methods.
Internal stresses can be introduced into the mater­
ial by improper frame straightening. For this
reason the following restrictions should be ad­
hered to completely:
1. Fram e straightening should be attempted
only by experienced personnel.
2. Heat may be applied toS.A.E. 950, o r S .A .E .
1023 steel only by competent personnel. The m a­
terial temperature should not exceed 1200° (dull
red glow). It must be strongly pointed out that ex­
cessive heat will damage the material structure
characteristics of the frame rail.
3. Fram e members which are bent or buckled
sufficiently to show strains or cracks after straight­
ening should be replaced.
IDENTIFICATION OF MATERIAL
The importance of properly identifying the
base rail before attempting to straighten or repair
cannot be overemphasized. The results of incor­
rect welding or straightening methods may cause
more damage to the frame than was originally ex­
perienced. For all practical purposes the S .A .E .
1023 and S .A .E . 950 material may be treated in
the same manner.
The standard models as quoted in the
Chevrolet Data Book describe the physical dimen­
sion of the frame rail and specify the type of
material used. However, due to the number of
R P O 's and Special Quotations available on most
models, the Data Book inspection is not always a
valid identification. The material identification
may be made by checking the vehicle chassis
number against the original sales order. This
may be checked at the selling dealer or at the
Zone Office.
Any reinforcements added must be of the
same or better material than the base frame rail.
This would permit the use of SA E 950 reinforce­
ments on S .A .E . 1023 base-rails.
M o x . B e n d in g M o m e n t
T -29 93
Figure 2 — Frame Bending Moment (Typical Tractor)
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L