Lesson 3/Learning Event 1
To provide a rigid foundation for the vehicle body, as well as a solid mounting for the
suspension system, a frame of some sort is necessary. The plan and construction of a
frame depends upon the type of vehicle and the service for which the vehicle is intended.
Two major types of frames are in common use. They are the conventional frame and
the integral frame. The conventional frame is made separately from the body, and the
various vehicle parts are bolted to it. In the integral-type frame, the frame and body are
made as a unit and welded together.
Conventional frames for passenger cars and trucks are built of side rails, cross-members,
and gussets. Gussets are angular pieces of metal used for strengthening points where the
side rails and cross members join. These parts, when riveted together, look like some
form of a letter, such as "A," "X," "Y," or "K." The assembled frame combines stiffness
and strength with light weight.
The conventional frame is usually not more than 30 inches wide in front so that the
wheels will not rub on it when making a sharp turn. It may be widened to 48 inches at
the rear for increased body stability. Kickups (humps) over the axles allow the vehicle
body to be set closer to the ground.
For large trucks, the frames are simply made of rugged channel iron. The side rails are
usually set at standardized widths to permit the mounting of stock transmissions, transfer
assemblies, axles, and so forth. Trucks used as wreckers or tractors have additional
reinforcement of the side rails and rear cross-members.
The frame members serve as supports to which suspension arms, radiators, transmissions,
and the like may be attached. Additional brackets and supports are added for the
mounting of running boards, springs, bumpers, engines, towing hooks, shock absorbers,
gas tanks, and spare tires. Rubber insulator blocks are usually used between the frame
and body attachment points to reduce vibrations and road noise.
In the integral-type frame, various body sections are used as structural strength members.
All these sections are welded together into what is usually referred to as the "unitized"
body and frame.