GMC 4000 Series Service Manual page 107

Sec. 2
Page 100
FRAME
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 the frame
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 "FR" equals "FL" and "DR"
equals "DL." 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 "ER" equals "EL" and "GR"
equals "GL." NOTE: 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 Fram es
The practice of straightening fram es should
not be attempted by inexperienced personnel, as
more damage can result from improper methods.
Internal str e sse s can be introduced into the mater­
ial by improper fram e straightening. For this
reason the following restrictions should be ad­
hered to completely:
G M C S E R V I C E M A N U A L
only by experienced personnel.
only by competent personnel. The material temp­
erature should not exceed 1200° (dull red glow).
It must be strongly pointed out that excessive heat
w ill damage the material structure characteristics
of the frame rail.
sufficiently to show strains or cracks after straight­
ening should be replaced.
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. Frame str ess concentrations resulting
from improper welding methods are a major cause
of future frame failures.
Data Book describe the physical dimension of the
frame rail and specify the type of material used.
However, due to the number of RPO's and Special
Quotations available on most models, the Data
Book inspection is not always a valid identification.
cut-out in the frame side rail at the front axle
center line.
or better material than the base frame rail. This
would permit the use of S.A.E. 950 reinforcements
on S.A.E. 1023 base rails.
Max. Bending Moment
Figure 2 — Fram e B e n d in g M o m e n t (Typical Tractor)
1. Frame straightening should be attempted
2. Heat may be applied to S.A.E. 1023 steel
3. Frame members which are bent or buckled
IDENTIFICATION OF MATERIAL
The importance of properly identifying the
The standard models as quoted in the GMC
The material can be identified by the type of
Any reinforcements added must be of the same
T-2993