SECTION 5 FRAME MODIFICATIONS
INTRODUCTION
Peterbilt offers customer specified wheelbases and frame overhangs. So, in most cases frame modifications should not
be necessary.
However, some body installations may require slight modifications, while other installations will require extensive
modifications. Sometimes an existing dealer stock chassis may need to have the wheelbase changed to better fit a
customer’s application. The modifications may be as simple as modifying the frame cutoff, or as complex as modifying
the wheelbase.
DRILLING RAILS
If frame holes need to be drilled in the rail, see SECTION 4 BODY MOUNTING for more information.
MODIFYING FRAME LENGTH
The frame overhang after the rear axle can be shortened to
match a particular body length. Using a torch is acceptable;
however, heat from a torch will affect the material
characteristics of the frame rail. The affected material will
normally be confined to within 1 to 2 inches (25 to 50mm) of
the flame cut and may not adversely affect the strength of the
chassis or body installation.
CHANGING WHEELBASE
Changing a chassis’ wheelbase is not recommended.
Occasionally, however, a chassis wheelbase will need to be
shortened or lengthened. Before this is done there are a few
guidelines that should to be considered.
WARNING! When changing the wheelbase, be sure
to follow the driveline manufacturer’s
recommendations for driveline length or angle
changes. Incorrectly modified drivelines can fail
prematurely due to excessive vibration. This can
cause an accident and severe personal injury.
Before changing the wheelbase, the driveline angles of the
proposed wheelbase need to be examined to ensure no
harmful vibrations are created. Consult with the driveline
manufacturer for appropriate recommendations.
Before the rear suspension is relocated, check the new
location of the spring hanger brackets. The new holes for the
spring hanger brackets must not overlap existing holes and
should adhere to the guidelines in the “FRAME DRILLING”
section of this manual.
When shortening the wheelbase, the suspension should be
moved forward and relocated on the original rail. The rail
behind the suspension can then be cut to achieve the desired
frame overhang. See FIGURE 5-1.
FIGURE 5-1. Wheelbase Customization
