Chevrolet 70 Series 1970, Service Manual

Page: 706 / 841

STEERING SYSTEM 9-27
On a ll hydraulic pump m odels, the fluid r e s e r ­
voir eith er e n c a se s the pump or is mounted on top
of the pump. An additional r e se r v o ir is mounted on
a bracket attached to the radiator support on con­
ventional cab m odels or to the tra n sm issio n con­
tro l islan d panel front support on tilt cab m odels.
When the slig h te st evidence of dirt, sludge,
or w ater is d iscovered in the sy ste m , drain and
r e fill with clean hydraulic fluid recom m ended in
LUBRICATION (SEC. 0). To drain sy ste m , d isco n ­
nect fluid lin e s at pow er cylin d er. A ir in the fluid
sy ste m w ill cau se spongy action and noisy op er­
ation. When any h ose has been disconnected or
when fluid has been lo st for any reason, the s y s ­
tem m ust be bled after adding fluid. B leed sy ste m
as d irected la ter in this sectio n under "Bleeding
H ydraulic S y ste m .” Should the power steerin g s y s ­
tem becom e inoperative due to lo s s of hydraulic
fluid, pump p r e ssu r e lin e should be r e-ro u ted from
pump outlet d irectly back to pump r e s e r v o ir or
disconnect drive b elt.
IMPORTANT: Do not operate pump without
fluid in pump r e se r v o ir .
The hydraulic pump, control valve, and power
cylinder do not req u ire adjustm ent on the v eh icle.
The only adjustm ents a r e on the ste er in g linkage.
Adjustment of th e se p arts a re norm ally required
only when the units have been rem oved or d is­
connected.
NOTE: T hese adjustm ents, with the exception
of the pow er cylinder p iston rod end, a re the sam e
as p rev io u sly d escrib ed in "MECHANICAL STEER­
ING" of this group.
W heel alignm ent m ust be m aintained to proper
sp ecifica tio n s. R efer to "FRONT END ALIGN­
MENT" (SEC. 3A) of th is manual for proper p ro­
ced u res for checking front end alignm ent. Im­
proper tir e inflation w ill a lso affect operation of
the pow er ste e r in g . The t ir e s , th erefo re, should
be checked at regular in terv a ls.
B eca u se of the pow er a s s is t from the power
ste e r in g sy ste m it is m ore difficult to detect de­
fe c ts in the ste e r in g sy ste m . T herefore, p eriod ic
maintenance is very im portant on a veh icle having
pow er stee rin g .
BLEEDING HYDRAULIC SYSTEM
When a power ste e r in g pump or pow er cy lin ­
der has been in stalled or a disconnected o il line
has been reconnected, the air that has entered the
s y s te m must be bled out b efore the v eh icle is again
operated. If air is allow ed to rem ain in the hy­
draulic fluid sy ste m noisy and u n satisfactory o p er­
ation of the steerin g sy ste m w ill r e su lt. B leed air
from the hydraulic sy ste m as follow s:
NOTE: When hydraulic fluid is added to power
Figure 2—Power Steering System
ISteel Tilt Cab Models) ITypical)
ste erin g sy ste m , fluid should be poured through a
200 m esh w ire sc r e e n . U se only the hydraulic fluid
recom m ended in LUBRICATION (SEC. 0).
1. F ill pump fluid r e se r v o ir to proper le v e l
and let fluid rem ain undisturbed for about two
m inutes.
2. R a ise front end of the v eh icle so that front
w h eels a re off the ground.
3. Turn w h eels to right and left to w heel
"stops" to elim inate a ir pockets in the pow er c y l­
inder. Continue th is operation until fluid in r e s e r ­
v o ir stop s bubbling. Maintain fluid le v e l during
th is operation.
4. Start the engine and run at id le for two
m inutes, turn w h eels to right and left a s b efore.
Figure 3 —Checking Pump Hydraulic Pressure
(Vane Type Pump) ITypical)
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL