By Gene Markel
The “Edge Code” can tell you information about the product you are about to sell. These letters and numbers help technicians select the right friction material for a vehicle and its driver.
Edge Code is a language written by engineers, federal entities and industry associations.
Like any language, edge coding has its own “grammar” that has been
defined by standardized vehicle and laboratory tests. If you are to
take one thing away from this article, it should be how to read the
letters that correspond with the friction levels of the brake compound.
These two letters are midway through the code, but to understand them,
you must first understand the tests behind the letters.
is a resistive force that prevents two objects from sliding freely
against each other. The coefficient of friction: The Greek letter μ
(pronounced “mew”) is a number that is the ratio of the resistive force
of friction (Fr) divided by the normal or perpendicular force (Fn)
pushing the objects together. It is represented by the equation: m = Fr
coefficient of friction and resistance to fading is measured using
Society of Automotive Engineers (SAE) practice J661 and marked with SAE
Practice J688 (truck standard). Stay with me here, when you see a SAE
JXXX code or practice
don’t think that it is useless to a technician. Keep in mind that when
SAE publishes these standards it has been reviewed and tweaked by all
concerned parties like OEMs, suppliers and governmental bodies in some
cases. In the cases of J661 and J688, it has direct bearing on the
aftermarket technician. The purpose of J661 and J688 is to establish a
uniform laboratory procedure for securing and reporting the friction
and wear characteristics of brake linings.
performance data obtained can be used for in-plant quality control and
for the quality assessment of incoming shipments by the purchasers of
brake linings. But, the data is also used in determining the edge code
and the right friction material for a vehicle.
has its roots in a Ford test that was developed in the 1960s. This is
why the test takes place in a simulated drum brake. It is a simple test
that just about every friction material formulation has to endure.
SAE Practice J661 and J688 testing procedure takes place on a machine that contains an 11-inch drum with three
drum can also be heated during the test. But, the drum is turned at a
constant speed. The SAE Practice J668 and J661 for the edge code on
friction material notes the normal coefficient of friction and hot
coefficient of friction or fade resistance. Letters are used to note
the coefficient of friction as shown in the table above. In the edge
code, the first letter notes the normal coefficient of friction and the
second letter notes the hot coefficient of friction. The code appears
in 0.25-inch letters on the edge of the friction material.
measurement results are not indicated in the edge coding. It does not
mean that the car will stop in a safe distance or will not make noise.
Edge code should only be used to determine if the friction material
will match what was installed on the vehicle for cold and hot friction.