Rust and the unit body Ford
A guide to common, yet hidden rust in 20+ year old salt belt cars
by Brent Peterson
After twenty years in a northern environment where road salt is the
norm, steel can suffer greatly, particularly after the coatings designed to
protect the metal begin to break down due to age. There are many
common areas under the car that normally suffer at the hands of the
demons of salt and rust. Most un-restored cars that have been driven
in winter most of their life will likely have rust somewhere on the underside.
In my travels I have seen many older Mustangs, Torinos, Fairlanes and other
unit body Ford automobiles that appeared in great to easily fixable condition
from above, yet below were a total mess. It would seem that for many cars the
body was repaired, but the underside was allowed to continue to rust.
This guide is intended to point out these areas which in cases of severe damage
could make a car unsafe to drive. While no car will have damage in all the
areas described below, it is common to find at least surface rust in one
Each region of the underside of the car has its own places were rust can take
hold and do its evil work unseen, the front third of the car contains
most of these places. The most forward of these just rear of the lower control
arms. The support for the lower control arm has a flange that extends along
the bottom of the frame rail. This flange is a prime location for the development
of a very destructive rust. The rust will eat its way clear into the frame rail
if allowed to go unchecked. The next location is just to the rear of the first
in fact they can become one rust hole. Rust will attack the frame rail where
the steering box or idler arm is mounted from the inside of the frame rail.
This takes us to the junction between the frame rails and the torque boxes,
and into the middle third of the car.
The middle third is straight forward, there are two areas that are most prone to
rust in this region. The first is the torque box and its junction to the front
frame rails. The torque boxes are located just rearward of the front wheels
under the front passenger's feet. These pieces are made of a heavy gage steel
and were designed to make the unit body more rigid. The only other area prone
to rust in the middle third are the floor pans themselves.
The rear third can hide its rust very well, and a casual inspection will not
revel it unless the exact locations are checked. The first and most
important are the rear frame rails behind the rear leaf spring shackle.
Inside the frame rail there is an inner piece which the shackle is bolted to,
it is the frame rail its self that normally will rust, weakening the leaf
spring connection to the frame. In the trunk, the trunk floor can rust along
its connection to the rear frame rails, and then creep along to the wheel
wells. The flat regions of sheet metal, (underside of the trunk floor) between
the gas tank and the rear frame rails, must also be checked for rust.
This section will deal with a quick overview of common body rust that can be
repaired, at worst with new body panels. Underhood, the seams between the
sheet metal parts should be checked, and under the hood lip. In the front wheel
wells the rear part, inward of the plastic guard needs to be checked. The
fenders will normally rust at the bottom between the front wheels and doors.
The lower part of door skin and door drain holes areas require inspection. In
the rear wheel wells, all the sheet metal should be checked inside and outside
of the wheel well.
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