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There
is no big secret on measuring leaf springs, just a bunch of bad information.
Remember
the guy back at the beginning of the Tech Section?
He has
spread a lot of bad information that we are about to correct.
The
WRONG way to measure is eye to eye. While this may seem to be the easiest, it is not
accurate.
The measurement you get is only good as long as the spring stays at
that arch.
As a spring flexes up and down, the distance between the eyes
changes.
A
48-inch (measured the correct way) with a 6-inch arch will
measure 46-3/4 inches eye to eye.
The same spring with a 3-inch arch will
have an eye to eye measurement of 47-3/4 inches.
Also
if
you would like your axle to be in the right spot, the location of the
center-bolt is very important.
Measuring eye to eye will not
tell where
the center-bolt is located and the chances of
your
axle being in the right spot
are not good.
So
the ONLY way to measure the length of a spring is as though the spring
was flat.
Follow
the curve of the spring measuring from the center of the front eye back
to the center bolt (A).
Then
measure from the center of the other eye back to the center bolt (B).
These
measurements are called the "Divisional Length" and are
indicated as 2 different lengths. Using
the 48-inch spring from above could have several "Divisional Lengths". 24 x 24, or 21 x 27 or
20 x 28 or whatever.
Spring
Arch is measured by splitting the center of the spring's eyes with a
straight edge.
Then
measure down from this line to the top of the Main Plate next to the center
bolt (C).
(the
Main Plate is the leaf with the eyes)
This
measurement can be positive or negative. A spring does not care which way
it is bent, they will work both ways.
Setting
the spring upside down and measuring from the floor to the main plate or
to the bottom of the spring is WRONG, WRONG,
WRONG. So don't even try to give us a measurement done that
way. Why?
Because the support for the vehicle is through the center of the eyes not
on the top of the eyes. Plus steel thickness, eye sizes, eye shapes can
vary. Plus, all the OEM's measure through the eyes and all our specs are
through the eyes, so do it our way.
Free
Arch is the term used for the arch when the spring is unloaded (off the
vehicle).
Loaded
Arch is when the spring is under load (on the vehicle with weight on the
springs).
To
make it easy for you we have created a cheat sheet, download our Leaf
Spring Measuring Form.
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