Chevrolet 70 Series 1970, Service Manual

Page: 708 / 841

STEERING SYSTEM 9-29
c. If '.'New" b elt, position pump to obtain 103
to 113 pounds.
d. Tighten pump attaching bolts fir m ly .
NOTE: A P o ly -V b elt is considered "Used"
after one-hour's operation or approxim ately 50
m ile s operation.
2. Adjusting Ordinary V -B elt
U sing Strand Gauge (J-23573)
NOTE: Gauge should be placed at the center
o f the g rea test span of the belt.
a. L oosen pump mounting b olts.
b. If "Used" belt, p osition pump to obtain 80
to 90 pounds.
c . If "New" b elt, p osition pump to obtain 120
to 130 pounds.
d. Tighten pump attaching bolts firm ly .
NOTE: A V -b elt is considered "Used" after
The 553-DV and 568-DV type pow er steerin g
gear a sse m b lie s a r e b a sica lly the sam e except for
s iz e and mounting. The 568-DV type steerin g gear
in corp orates a back-up adjuster to prevent the
w orm shaft from flexin g up and down and "stops”
are countersunk at each end of the worm shaft to
prevent the ball nut from bottoming on extrem e
tu rn s. R efer to "Model Application" at end of this
se ctio n for ste e r in g gear application.
CONTROL VALVE
The pow er ste erin g sy ste m control valve is
mounted on top of the steerin g gear housing and is
activated by a torsion bar that tends to keep the
valve in neutral position . Should the torsion bar
break, the spool and valve body "lock up" into a
com plete unit that then op erates m echanically.
The valve shown in figu re 5 is an op en -cen -
tered , rotary-typ e, th ree-w ay valve. The spool is
held in the neutral p osition by m eans of the torsion
bar. The spool i s attached by m eans of a stud fa s ­
tened to one end of the to rsio n bar and the valve
body to the other end. T w isting of the torsion bar
allow s the spool to d isp lace in relation to the valve
body, thereby operating the valve.
tw o-h ou r's operation or approxim ately 50 to 100
m ile s operation.
TUBES, HOSES, AND FITTINGS
Stationary tubes and flex ib le h o ses a re u sed
to carry hydraulic fluid through the pow er steerin g
s y ste m . T hese tubes and h o ses connect the s te e r ­
ing gear to the pow er cylinder and hydraulic pump.
NOTE: On som e v e h ic le s equipped with the
F -1 6 0 front a x le, and junction block is u sed b e­
tween the control valve and right and le ft pow er
cy lin d ers. Tag each tube or h ose p rio r to rem oval
to in su re in stallation in sam e rela tiv e location.
A ll tubes, h o se s, and fittin gs should be in sp ec­
ted for leakage at regular in terv a ls. F ittin gs must
be tightened to torque lis te d in "Specifications" at
end of th is sectio n . Make su re c lip s, clam p s, and
unions supporting tubes and h o ses a r e in p la ce and
properly secu red .
CONTROL VALVE OPERATION
When the valve i s in neutral or straigh t-ah ead
p o sitio n , the fluid flow s from pump through the
op en -cen ter valve, and back to pump r e se r v o ir ,
without travelin g through the power cylin d er. T his
op en -cen ter p osition of the valve red u ces pump
l o s s e s to a minim um . V alve is in op en -cen ter p o s i­
tion at a ll tim e s except when turning. The power
cylinder is alw ays fu ll of fluid, which a cts a s a
cushion to absorb sh ock s so that they a re not tra n s­
fe r r e d to the d riv er. T his fluid lu b ricates a ll of the
internal com ponents of valve, making it u n n eces­
sa r y to lubricate the valve.
With the ste e r in g w heel turned to the right, the
to rsio n bar i s d eflected , changing the relationship
of the spool gro o v es and valve body g rooves with
each other. The right-turn grooves of the spool
a r e closed off from the return grooves and opened
to the p r e ssu r e g ro o v es. The left-tu rn g rooves of
the spool are c lo sed off from the p r e s s u r e grooves
and opened to the return g r o o v es. T his ca u ses the
fluid to flow into the appropriate half of the power
cylin d er, overcom ing the tir e frictio n in that di­
re ctio n . The fluid in the opposite end of the cylinder
i s sim ultaneously forced out through the valve and
back to the pump r e se r v o ir .
POWER STEERING GEAR AND CONTROL VALVE
NOTE: T h ese control valve and P ow er Steering Gear fa sten ers a re important
attaching p a rts in that they could affect the perform ance of vital com ponents and
s y s te m s , an d /o r could re su lt in m ajor repair exp en se. They must be rep laced with
one of the sam e part number or with an equivalent part if replacem ent becom es
n e c e ssa r y . Do not u se a replacem ent part of l e s s e r quality or sub stitu te design.
Torque valu es must be u sed a s sp ecified during rea ssem b ly to a ssu r e proper r e ­
tention of th is part.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL