G Model Underbody; D E S C Rip Tio; Underbody A Lig N M E N - GMC 1986 P-Truck Service Manual

15. Front Gage Holes
16. Rear Gage Holes
A. 789.4 mm (31.08-inch)
B. 1041.4 mm (41.0-inch)
C. 1340 mm (52.76-inch)
D. 1041.4 mm (41.0-inch)
E. 126 mm (4.96-inch)
F. 123 mm (4.8-inch)
G. 113.3 mm (4.46-inch)
H. 13 mm (0.51-inch)
I. 96 mm (3.78-inch)
J. 145.2 mm (5.72-inch)
K. 701 mm (27.6-inch)
DESCRIPTION
The G Model incorporates a unitized body design
comprised of side rails, cross sills, and outriggers
which are all part of the welded underbody.
A misaligned underbody can affect the opeartion of
many ve hicle com ponents. It is e ssen tia l that
underbody alignm ent be exact to within 1.6 mm
(1 /i e-inch).
UNDERBODY ALIGNMENT
To determine the alignment of the underbody it is
necessary to use a good quality traming gage. This
gage must be capable of measuring all points of the
underbody up to three quarters of the body length.
Following the instructions given by the manufacturer
of your gage, measure the horizontal and vertical

G MODEL UNDERBODY

L. 1465 mm (57.66-inch) 110-inch wheelbase
1845 mm (72.66-inch) 125-inch wheelbase
M. 2772 mm (109.17-inch) 110-inch wheelbase
3153 mm (124.17-inch) 125-inch wheelbase
N. 2833 mm (111.54-inch) 110-inch wheelbase
3442 mm (135.54-inch) 125-inch wheelbase
Figure 3—G Model Underbody
p o in ts as show n in fig u re 3. C o m pare each
measurement with the specifications given in the
figure to determine the damaged areas and the extend
of the damage. When repairing the underbody it will be
necessary to return the underbody to these original
specifications within 1.6 mm (1 /ie-inch).
Many different types and brands of unibody repair
equipment are available; each system may be slightly
different. A multiple pull system is most desirable in
order to correct the damage in the same direction in
which it was created. When making multiple pulls use
the last in, first out procedure. This means that you
correct the damage in the reverse sequence by which
it was created. It is also important to correct the
damage in the opposite direction in which the damage
was created.
FRAME 2A-7
B-09120