American Motorcycle Dealer AMD 230 September 2018 | Page 56
TECH EXTRA
Whip Test
Tensile
different pull rates until failure occurs. This test
literally stretches a brake hose assembly until it
either pulls off one of the crimped end fittings, or
the hose itself fails by tearing or fraying,
whichever occurs first.
The hydraulic brake hose assembly must
withstand a pull of 325 lbs during a slow pull test
and 370 lbs during a fast pull test, without
separation from its end fittings. Designing the
crimp joint to meet this specification must not
compromise the constriction test due to over-
crimping the fittings to increase pull-off.
This is one of the most difficult of all the tests to
pass due to the enormous stresses that the hose
is subjected to. This is especially true for stainless
steel braided lines which experience metal fatigue
when being bent continuously on a flexing
machine at 800 rpm for a grueling 35 hours.
For an onlooker, the brake hose looks like an
airplane prop, a mere blur, and failures usually
occur on the hose at or near the stationary end
fitting. The assembly’s hose couplings are
mounted on the machine with a very specific
amount of slack added to the line, depending on
the length of the test sample. Each end is then
locked down with no ability to spin, which would
otherwise reduce the stresses on the assembly.
The brake hose assembly is then pressurized with
water and monitored via pressure sensors. During
the duration of this test, if there is any detection
of a drop in pressure from the fittings or hose, it
is deemed a failure. This test ensures that the
fittings and hose are designed and manufactured
robustly enough to perform on the vehicle over
the long term without mechanical failures from
vibration, movement or flexing.
Water Absorption
Tests
Because brake hose assemblies are constantly
being subjected to rain, splashing water, and
steam from hot exhaust tubes, this test’s recipe
calls for three hose assemblies to be completely
immersed in distilled water at 185° F for 70
hours.
Within 30 minutes after removal from the water,
they must be subjected to, and pass, the previous
three tests again - Tensile, Burst and Whip. Due to
the possibility of the hose materials being mildly
hydrophilic, water may be absorbed and its
physical properties may be altered. This may lead
to the assembly experiencing more difficulty
passing these three tests.
High Temperature
Impulse Test
This is a rather intense test designed to ensure
the durability of the brake hose assembly by
simultaneously subjecting it to heat and pressure
cycling. For approximately 5 hours, an assembly
Whip
Burst Strength
The Whip Test is one of the most difficult of all the tests to pass due to the enormous stresses that
the hose is subjected to
Burst
This is a fun and sometimes loud test. The
hydraulic brake hose assembly must withstand
water pressure of 4,000 psi for two minutes
without rupture. Popular motorcycle brake hoses
that have an I.D. of 1/8” must be tested to 7,000
psi. Hoses need not be burst to pass this test, but
it may be noted that some 1/8” hoses with high
tensile stainless steel or aramid fiber
constructions may exceed 25,000 psi before
rupturing, and when they do, they do it with a
bang!
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AMERICAN MOTORCYCLE DEALER - SEPTEMBER 2018
www.AMDchampionship.com