GMC 1982 Light Duty Truck Service Manual page 146

2 A -4 FRAME
Bolting
W herever rivets or failed bolts are replaced, bolt hole
must be as near the O.D. of the bolt as possible to prevent
bolt from working and wearing. Drill out and line ream hole
(or holes) to the bolt O.D.
UN DERBO D Y A L IG N M E N T
O ne m ethod of d eterm in in g the alig n m en t of the
underbody is with a tram gage which should be sufficiently
flexible to obtain all necessary m easurem ents up to three
quarters the length of the vehicle. A good tram m ing tool is
essential for an aly zin g and d eterm inin g th e ex ten t of
collision m isalignm ent present in underbody construction.
M E A S U R IN G
To m easure the distance accurately between any two
reference points on the underbody, two specifications are
required.
1. The horizontal dim ension between the two points to be
tram m ed.
Fig. 2 A -4--G Van Truck Reference Dimensions
2. The vertical dimension from the datum line to the
plane. The exception to this would be when one of the
reference locations is included in the misaligned area; then
the parallel plane between the body and the tram bar may
not prevail. A fter completion of the repairs, the tram gage
should be set at the specified dim ension to check the
accuracy of the repair operation.
EXCESSIVE BO D Y D A M A G E
suitable as reference points, repair operations should always
begin with the underbody area. All other components should
be aligned progressively from this area. Unlike the conven­
tional type of fram e design, the unitized type of body
construction seldom develops the two conditions of "tw ist"
and "diam ond" in the underbody area as a result of front or
rear end collisions, therefore, there usually is an undam aged
area suitable as a beginning reference point.
points to be tram m ed.
The tram bar should be on a parallel to th at of the body
If dam age is so extensive th a t key locations are not