This page involves the use of leaf springs, mounted in their "normal" location.
This would be typical of the Fords, Chevrolets, and Plymouths of the fifties. However, in this case,
shackles will be used in BOTH the rear and front spring eyes. In other words, though a leaf spring is
usually called upon to carry horizontal loads, these springs...with shackles at both ends...can only
carry vertical loads.
So, why not use coil springs? Well, there are a couple of reasons. First,
there are those who compete in classes where they are required to retain the spring type as
originally supplied. Also, the "lowly" leaf spring supplies a surprisingly beneficial function!
Since the leaf spring does not pivot at it's connection with the axle housing, the front half of
the spring extends forward as an "arm," similar to a ladder bar or the arm of a torque arm
suspension. It occurred to me, then, that the leaf spring suspension could be easily converted to a
torque arm suspension, merely by the inclusion of the aformentioned shackles, one or two links, and a
By saying "one or two links," a decision is implied. That decision would be
similar to the one made between a 3link and a 4link. Actually, the decision is not similar, but is
EXACTLY the same. Those two forward shackles are short, vertical links. Whether you add a single link
or two links determines whether the final suspension is a 3link or a 4link. In either case, the
instant center location...and consequent amount of antisquat...is found by the intersection of the
link lines, as viewed from the side. The degree of adjustability is up to the fabricator.
equal rear tire loading and no twisting of the chassis is desired, a single link is the proper
solution. Since that single link will be in compression during launch, it would normally be offset to
the left (US driver side). This would mean, however, that the axle housing would tend to rotate about
the rear mount of that link. To cancel that effect, the link would normally be rotated
counter-clockwise in plan view (looking down from above). This would provide a side force, which,
when reacting against the Panhard rod. would provide a cancelling couple. This side force, acting at
the height of the rear pivot point of the link, would also provide a moment which would help to cancel
the driveshaft torque.
The spreadsheet provides the offset and the link plan angle. The
"angle," "distance," and "height" require explanation. "Angle" is link angle when viewed from the
side, with a positive angle existing when the rear pivot point is higher than the front pivot point.
"Distance" is the plan distance from the link rear pivot location to the Panhard rod. "Height" is the
vertical distance to the link rear pivot."Angle" is input in degrees and "distance" and "height" are
Of course, if all that's desired is the equivalent of
an adjustable 4link, this spreadsheet is of no value. Simply find your links intersection point for
the desired percent antisquat and you're done.
Finally, remember that a single link is
carrying more than double the load of two links! Saving a couple of pounds of car weight is never to
be valued above safety. Also, track and tire irregularities can easily cause high loading on those
fabbed front shackles. Don't count on link placement and angles to completely cancel out high side