BRP ski-doo MACH Z 1000 SDI, Handbook

Page: 46 / 493

03-16
MMC2005-001_03A.FM
SECTION 03 - CHASSIS PREPARATION
SHOCKS
Valving and Dampening
In the HPG shock, the piston passages are cov-
ered by a stack of thin metal shims of various
thicknesses and diameters. The shims provide
dampening by acting as spring loaded valves offer-
ing resistance to the oil traveling through the pis-
ton. There is a stack of shims on both sides of the
piston. One side controls compression dampen-
ing and the other side controls rebound dampen-
ing. By varying the number and thickness of shims
the dampening characteristics can be very accu-
rately obtained. There may also be orifices or slits
in the piston that are not covered by the shims.
These are referred to as bleed slits. The size and
number of these slits will also affect dampening.
The external adjustment on the MVA, HPG shocks
is a variable bleed hole.
Rebound dampening will usually be much stiffer
than compression dampening. This is because re-
bound dampening must resist the force of the
spring and because piston speeds are much slow-
er during rebound.
At low piston speeds, the number of bleed slits
will have a fairly large effect on dampening, but as
piston speeds increase most of the dampening is
controlled by the shim stack. This is because the
flow area of the slits is much smaller than the flow
area under the shims. Since only a small amount
of oil can flow through the bleed slits (compared
to the amount that flows under the shim stack),
the slits have only a very small effect on dampen-
ing at high piston speeds. Because of this charac-
teristic, bleed slits are most effective on rebound
dampening. They will have only a very slight effect
on compression damping because the typical pis-
ton speeds on compression strokes are several
times faster than on rebound strokes. There really
is no such thing as
high speed rebound dampen-
ing.
A01F26A
EFFECT OF BLEED SLITS
Compression
Piston speed
Dampening
force
0
0
No
bleeds
2 bleeds
4 bleeds
6 bleeds
Rebound
Piston speed
Dampening
force
0
0
No
bleeds
2 bleeds
4 bleeds
6 bleeds