3-72. Lift System Main Control Valve
(1) Grease new O-ring seal on the relief car-
tridge and install this end of cartridge into ad-
a. General. The main control valves are mounted
justment side of valve body. Tap slightly with a
next to the driver's compartment. The control
rawhide mallet until cartridge bottoms.
v a l v e s are: lift, tilt, extension, oscillating, and side
shift. On RTL10 model there is a crane winch
D o not damage the relief poppet hole in
valve. Each valve is hydraulically operated. The
the end of the cartridge.
v a l v i n g arrangement is such that, with all operating
(2) Tighten relief cap to 45 foot-pounds
v a l v e spools in neutral position, the oil flow from
t h e pump will circulate freely through the various
(3) Place relief poppet valve and spring in the
valve sections back to the tank.
relief cap. Be sure the poppet valve is seated in the
b. Removal. Refer to figure 3-143 and remove
main control valves.
( 4 ) Install remaining parts of relief valve and
c. Disassembly. Refer to figure 3-144 and
tighten cap to 45 foot-pounds torque.
disassemble the main control valve. Mark relief
(5) Install each operating plunger in its
v a l v e to indicate adjustment side of control valve.
r e s p e c t i v e bore and center each plunger equidistant
f r o m each side of valve housing. Be sure wrench
( 1 ) Inspect the housing for cracks or damage.
f l a t s are on operating side of the valve.
(2) Inspect the load check for nicks and burrs.
(6) Install plunger seal in seal bore until it
( 3 ) Inspect the plunger for flaking of chrome
b o t t o m s . Absolute flatness of seal is necessary. Do
plating, cracking or other damage.
not distort seal or damage it in any manner.
(4) Inspect the poppet valve for erosion and
( 7 ) Tighten seal retainer plate screws to 15 to
wear. Normal operation will show only an ac-
20 foot-pounds torque.
ceptable light line at the point of contact at the
(8) Use a new backup ring with each new seal.
c a r t r i d g e hole. Replace poppet valve that is eroded
Use the same care on all seals as used in step (6). If
o r excessively worn.
a seal is bottomed correctly, backup ring will be
f l u s h with valve housing surface.
An eroded poppet valve indicates a contaminated
(9) Torque plunger cap by holding plunger eye
w i t h a suitable tool and tighten to 30 foot-pounds
t o r q u e . This method will torque both the cap and
(5) Inspect each plunger bore for scratches,
burrs or gouges. Rotate plunger a complete
revolution to determine if plunger fits without
(10) Tighten plunger cover screws to 15 to 20
binding. Plungers are a select fit in their bores.
(6) Check the plunger eye for damaged
f. Adjustment. Adjust relief valve to 2000 psi
threads or wear at the pin hole. Repair or replace a
with adjusting screw.
d e f e c t i v e plunger eye.
g . Installation. Refer to figure 3-143 and install
main control valve.
( 7 ) Replace all seals, fiber back up rings and
c. Reassembly. Refer to figure 3-144 and
reassemble main control valves as follows: