Section 6
Frame Modifications
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 6-1.
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