GMC 4000 Series Service Manual page 463

Sec. 7D
______________________ G M C S E R V I
Page 452
CLUTCH CONTROLS
Figure 12— Checking Adjustment of Slave
Cylinder Push Rod
SLAVE CYLINDER PUSH ROD
CHECK A N D ADJUSTMENT
This procedure is required periodically to
compensate for clutch facing wear. Purpose of
adjustment is to maintain a clearance between
the release bearing and the clutch release fingers
with clutch engaged.
IMPORTANT: The clearance between wedge
and adjusting nut on all models with hydraulic
clutch controls is 1/2-inch. A short ruler may
be used for checking the clearance.
NOTE: A tool for checking the 1/2" clear­
ance can be improvised locally as shown in figure
11. Perform the following when using this tool:
1. Disconnect the
spring.
2. With the push rod and piston seated in the
slave cylinder, push clutch fork and wedge on
push rod away from the slave cylinder. Insert
sm aller end of gauge on push rod between the
adjusting nut and wedge (fig. 12). If the tool will
not go between the nut and wedge the push rod
needs to be adjusted. If the small tool end fits
between the adjusting nut and wedge, the rod does
not require adjustment.
3. To adjust the push rod, use the thicker end
of the tool and insert between adjusting nut and
wedge on the slave cylinder push rod. Back off
adjusting nut until the tool just fits between the
slave cylinder return
E M A N U A L
nut and wedge.
4. Remove the tool, lock adjusting nut with
lock nut and install the slave cylinder return
spring.
BLEEDING HYDRAULIC SYSTEM
Use only Hydraulic Brake
mended in LUBRICATION (SEC. 0). When other
than recommended fluid has been used, drain
and flush the entire hydraulic system , using clean
alcohol or a hydraulic brake system cleaning
fluid. Disassem ble, clean, and inspect hydraulic
units. Replace all rubber parts.
RECOMMENDED fluid.
The need for bleeding air from system is
generally indicated by a springy, spongy pedal
action. The presence of air in system is a result
of low fluid level in master cylinder, or if some
part of system has been opened. Bleeder valve
is provided at the slave cylinder alongside of
clutch (fig. 14).
Plain end of bleeder hose can be slipped over
end of bleeder valve.
Clutch system may be bled either manually
or with pressure bleeding equipment.
PRESSURE BLEEDING
1. Make sure fluid level in fluid supply pres­
sure tank is up to petcock above outlet and that
tank is charged with 25 to 30 psi air pressure.
2. Clean dirt from around master cylinder
cover or cap. On units having reservoir cover
instead of cap, remove standard cover and install
special cover (J-8554).
hose to filler cap or special cover opening.
Bleed air from hose before tightening connection.
Open valves at both ends of hose.
3. Slip end of bleeder drain hose over bleed
valve at slave cylinder (8, figure 15) and place
the other end in a glass jar containing enough
hydraulic fluid to cover end of hose. Open bleeder
valve with wrench and observe flow of fluid from
hose. Close bleeder valve as soon as bubbles stop
and fluid flows in a solid stream.
MANUAL BLEEDING
Manual bleeding is the same as pressure
bleeding, except that the hydraulic fluid is forced
through the line by pumping the clutch pedal.
Fluid in master cylinder must be replenished
after bleeding. Clutch pedal should be pumped
up and down slowly, and should be on downstroke
as bleeder valve is closed.
Fluid recom­
Refill with
Connect pressure tank