Mike Sinclair wrote:
>
> expand on supporting a car with its suspension "drooping".
> This would be the same if it were up on jacks, right?
Yes, it's the same, but not exactly.
The suspension bushings consist of two metal tubes with "rubber" bonded in
between. The outer tube is usually a press fit into the a-arm. The inner
tube is slightly longer and when you tighten the suspension bolts, it clamps
the "frame" onto the inner tube, thereby preventing it from rotating.
The bushings don't allow any rotation of the tubes relative to their
surface, the entire motion that is permitted is provided by the twisting and
stretching of the rubber in the bushing. Leaving the rubber twisted for a
couple of days isn't a problem. For a couple of months, it will cause
degradation of the rubber in the bushing. As an example of the degradation,
I had my Elan on jack stands for a couple of years. When I got around to
replacing the bushings, six of the eight bushings on the front had the
rubber completely separated from the tubing of the bushing (I had planned on
replacing everything with new anyway).
As an example of this that most people have experienced is a simple rubber
band. I you've had a rubber band stretched around something for a long
time, chances are if you stretch it more (as in taking it off), the rubber
band will break. But the "new" one that you take out of the drawer to
replace it (that probably came out of the same package) will still be
springy and ready go for a long time.
This is also why, when you tighten the suspension bolts, the car needs to be
at ride height. If you assemble things and torque down the bolts and then
put the car on the ground, the bushings will be twisted as the car settles
on them. Two things will happen. One the bushings will fail rather
rapidly. Two, the suspension will be "pre-loaded" - the bushings will be
trying to "lift" the car, messing up the handling, and actually reducing the
suspension movement. It is a pain to two to settle the car before you
tighten things. Get it on the ground, and roll it back/forward a couple of
feet (as the suspension moves up, the tires will distort as they try to move
outward - rolling it eliminates the effect of the tire distortion. Then
comes the hard part, trying to reach under there to get the torque wrench on
the various bolts. But it is very necessary.
Hope this explains things in an understandable way...
Tim Mullen
Chantilly, VA
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