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[T3] Unibody T3????


Just had to get my 3 cents worth in here.....

The T3 is NOT a true unibody car.  It is also not a body-on-frame
design.  It is a hybrid of sorts.

A body-on-frame (like today's pick-ups) design uses a ladder
frame to provide the bending and torsional ܱJ4s to react
road loads and engine loads (torque).  The body is soft mounted
(for vibration and noise control) to the frame.

A unibody (99% of all cars today) design utilizes the cars body
to react road loads and engine loads.  Suspension points are on
the body and so are engine mounts.  The car's roof and and
pillars etc contibute significantly to the vehicle stiffness.

The T3 (and the T1 for that matter) is a mix of these two design
philosophies.  The engine and suspension of the T3 are mounted to
the pan (i.e. frame) which provides the significant portion of
the bending stiffness with its central tube tunnel.  The pan also
provides enough torsional stiffness to make a driveable chassis.
(Had one of those as a kid....just a VW pan with wheels and an
engine...but that is another story) However, since the T3 body is
bolted solid to the pan it will contibute significantly to the
torsional stiffness of the vehicle.  It also adds to the bending
stiffness. So it is somewhat like a unibody.

However, bolting the body on is not nearly as effective at
transfering load as welding would be.  Typical automotive bodies
are spot welded together with weld spacing of about 2".  This
spacing is important.  If the bodies were continuously welded
(not practical or cost effective) the torsional stiffness would
increase by as much as 15%.  With the T3's 6" or so spacing on
the pan to body bolts, the T3 body contributes significantly less
than it would if it was a true unibody with a 2" spaced spot
welded body structure.  The T3 would also not need the heavy
tunnel if it was a true unibody.

So the T3 is a hybrid structure.  Would I tow with one?  Maybe a
small trailer.  Remember we only have 60hp or so and we are
aircooled.

Later,
John Jaranson (former Ford body structure engineer)
'71 FI Auto Fasty

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