In reply to a message from Mike Eck sent Thu 14 Aug 2008:
First, they are not a good choice for a street driven vehicle with
a parallel-leaf spring suspension.
The rear axle on a leaf spring car travels in an arc described by
the front spring eye and the axle shaft centerline. Keep in mind
that a simple Panhard rod also swings in an arc, but in a plane 90
degrees out from the spring. This means that as the axle moves up
or down the rod exerts its own lateral force on the axle which may
be either the same or opposite to those of the cornering loads. It
will bind up where the axle arc does not coincide with the
transvers arc of the Panhard rod. They also will transmit lots of
road and suspension noise (maybe not an issue in an OTS with the
hood down) to the frame unless they are rubber bushed, which then
renders them less useful.
They also change the rear suspension roll center, which has a
distinct impact on the handling, adding a jacking effect to the
axle. Note that this won’t be the same for both a left and a right
hand turn. This is why you see the NASCAR boys, who only ever turn
left, save for the two road races they run, running their Panhard
bar frame-end pivot points up or down at each pit stop. Done
skillfully, changing the frame pivot point can cure or create
understeer or oversteer.
There is also not really much room to mount one in a 120 where the
battery boxes and fuel tank are in the way, not to mention that the
frame members behind the front spring eyes are very slender, not
like the beefy Mk-V bridge-beam sections back to that point, so it
would be very tricky to devise a frame mount that would transmit
the forces somewhere where you would not be bending the frame.
If you feel you require more lateral location under load, I think
you would be better served by having four plastic shims (washers)
made that would restrict the lateral movement of the front spring
eye in the mounting pocket. It would fit over the protruding end
of the front bushing sleeve and replace the steel washer which is
already there. Going straight down the road they would do nothing,
even with the usual axle compression and rebound. Under lateral
load they would restrict the lateral deflection of the spring eye
Panhard rods are good for live axle oval track sedan racers where
the loads are always in the same direction. I know, I know, plenty
of road racers use them, but most of those cars have coil springs.
Best regards to all,–
The original message included these comments:
Has anyone ever installed a Panhard rod to better locate the rear axle?
Has anybody investigated whether this tire contact with the
skirt lock might be, at least in part, due to bad rubber
bushings in the leaf springs, allowing too much side
movement of the axle?
Mike Spoelker 672027
Louisville, KY, United States
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