Chevrolet Light Duty Truck 1973 Service Manual page 182

3-8 FRONT SU SPEN SION
EXTEN SIO N FORCE
Fig. 11—Shock Absorber Rebound Cut Off Schematic
shock absorber piston velocity. Figure 13 illustrates
rebound valving, and Figure 12 illustrates compression
valving. The three stages are described as follows.
Low Speed Orifice (First Stage)
Two low speed orifices control fluid passage during slow
body or wheel motions. The low speed orifice for
rebound consists of slots in the orifice disc of the
rebound valve, Figure 13, whereas the low speed orifice
for compression consists of depressions in the cylinder
end of the compression valve, Figure 12. This stage has
its major effect in controlling low speed body
movements. A very small, low speed orifice will cause a
harsh ride in which every bump will be felt, similar to
driving with over-inflated tires.
Blow-Off Valve (Second Stage)
Two blow-off valves, Figures 12 and 13, control the fluid
motion during intermediate body and/or wheel motion.
Depending on direction of stroke, the spring-loaded
RESERVOIR
COM PRESSION
blow-off valve opens as soon as the pressure is great
enough to unseat the valve, after which the low speed
orifice ceases to have an appreciable effect. As the
pressure of the fluid against the spring increases, the
valve continues to open until it reaches its maximum lift.
High Speed Orifice (Third Stage)
After the blow-off valve is completely open, further
increases in control at even higher piston velocities is
caused by restriction due to the high speed orifice.
Basically, there are two high speed orifices. The high
speed orifice on the rebound stroke is the holes in the
inner ring of the piston, Fig. 14. The high speed orifice
on the compression stroke is the hole in the compression
valve cage, Figure 12, in combination with the slots in
the outer ring of the piston. The high speed orifices are
large enough not to affect flow through the low speed
orifices or during the opening of the blow-off-valves, but
will quickly increase the control under conditions such as
wheel-hop, where high piston velocities are present.
COMPRESSION
VALVE ASSY.
BLOW OFF
VALVE
LOW SPEED
ORIFICE
Fig. 12—Compression Valve Parts
INTAKE VALVE
SPRING
HIGH SPEED
ORIFICE
--------- VALVE CAGE
■*
VALVE STEM
SPRING
RETAINER
WASHER
CYLINDER END
LIGHT DUTY TRUCK SERVICE MANUAL