CHASSIS AND ATTACHING SYSTEMS
twists, vibrations, and other strains (fig. 2-1). The
side members or rails are the heaviest parts of the
The chassis of a vehicle provides the strength
frame. The crossmembers are attached to the side
necessary to support the vehicular components and
members strongly enough to prevent twisting of the
the payload placed upon it. The suspension system,
frame. For added strength, angular pieces of metal
part of the chassis, contains the springs, shock
(gusset plates) are riveted or welded at the points
absorbers, tires, and wheels. The steering
where members are joined.
mechanism is also part of the chassis and
F r a m e s n o r m a l l y r e q u i r e ve r y l i t t l e o r n o
suspension, and it provides the operator with a
means of controlling the direction of travel. The
maintenance or service. Frames that have been bent,
transmission, propeller shaft, universal joints,
twisted, or broken, however, may be repaired if the
differential, axles, wheels, tires, brakes, and steering
damage is not too severe. Frame alignment can be
system are part of the chassis. The body or outer
checked in several ways. One way of checking the
portion of the vehicle encloses the mechanical parts
frame for forward alignment is by using frame gauges.
and passenger compartment, but is not considered
Frame gauges (each gauge has a sight mounted on its
part of the chassis. The components that make up the
center crossbar) are hung from the vehicle's frame in
chassis of the vehicle are held together in proper
three places. Frame alignment is checked by sighting
relation to each other by the frame.
from the front of the vehicle toward the rear. If the
NOTE: Basic Machines, NAVEDTRA 14037,
sights on the center of the gauges do not line up, the
has an entire chapter devoted to the power train. This
frame is out of alignment.
c h a p t e r c ove r s t h o s e c o m p o n e n t s t h a t a r e n o t
If the frame is out of line, it is usually permissible
adequately covered in Basic Machines, and some of
to straighten it, provided the lack of alignment is not
the applications and different arrangements of
power trains in support equipment.
too great. You should consult the appropriate technical
manual before you attempt to straighten the frame.
Most chassis repair jobs require work by
When frame members have been broken or so badly
mechanics under hoisted or jacked up vehicles.
distorted that they require replacement, new members
When new personnel report to your shop, never
can be installed with nuts and bolts or welded. The
assume that they have been instructed in the safety
precautions that must be observed when working
preferred method is to use hot rivets. When the front
under a vehicle. Personnel should be instructed in
suspension crossmember has been damaged, you
the use of jacks, safety stands, and other safety
normally replace it. The front suspension
devices used in your shop. After a person has been
crossmember is manufactured to such close tolerances
pinned under a falling vehicle, it is too late to give
that it is practically impossible to restore it to perfect
alignment by straightening. If the front crossmember is
not in line, the front wheels cannot be aligned, and the
result is poor steering and rapid tire wear.
For frame and chassis repairs that require welding
LEARNING OBJECTIVES: Identify the
and in-depth skin and rivet replacement, refer to the
purpose of the frame. Describe the working
applicable equipment technical manuals. Other
relationship between the frame and the chassis.
pertinent manuals include the Aeronautical and
Identify procedures for inspecting, checking,
and adjusting the frame.
S u p p o r t E q u i p m e n t We l d i n g M a n u a l , NAVA I R
01-1A-34; General Manual for Structural Repair,
NAVAIR 01-1A-1; and Structural Hardware, NAVAIR
The frame is generally constructed of steel, and it
is built rigid and strong so that it can withstand shocks,