JLG G6-42P Service Manual - Manual (Page 506)

GENERAL SERVICE DIAGNOSIS
Make sure the
machine is in a safe
and controlled state
before attempting
any servicing
including bleeding
the brake system.
With Engine Off --
PEDAL GOES TO FLOOR
SPONGY PEDAL
Air in system
Bleed brakes
PEDAL IS FIRM BUT STOPS TOO
NEAR FLOOR
Brakes out of adjustment
Adjust brakes
Inoperative brakes
Check for wear
Displacement problem
Wheel cylinders too large for
valve to handle properly.
Consider alternate braking
valve.
PEDAL IS FIRM BUT BRAKING IS
INADEQUATE TO STOP VEHICLE
IN EVENT OF ENGINE FAILURE
Pedal ratio too small
Increase pedal ratio
Brakes inoperative
Check brakes for wear or oily
brakes
With Engine Running --
PEDAL GOES DOWN PART WAY
THEN BOUNCES BACK
Insufficient flow from pump
Check and fill reservoir
Small volume from pump at idle
Crack throttle and recheck
Brake not adjusted
Check adjustment
Air in system
Bleed brakes
Inoperative brakes
Check brakes
Blown hydraulic line
Check brake line
Worn out primary cup
Check by making sure brakes
are properly adjusted, in good
operating condition, and
system well bled. If pedal
continues to go to the floor,
service brake valve.
Brakes not adjusted
Check adjustment
Air in system
Bleed system
NO POWER STEERING OR OTHER
DOWNSTREAM HYDRAULIC
ACTION AT ANY TIME
Hydraulic lines crossed
Recheck circuit
No hydraulic action at any time
Check and fill reservoir. Check
relief valve setting on pump.
Check for proper rotation at
pump, vee belt, sheared keys,
etc.
NO OR SLOW POWER STEERING
WITH BRAKES APPLIED
Recheck relief valve on pump for
proper setting
Check and fill reservoir
Check and tighten pump belt if
necessary
1.
1.
2.
2.
3.
3.
4.
4.
5.
5.
1.
1.
2.
2.
3.
3.
1.
1.
2.
2.
1.
1.
1.
1.
2.
2.
1.
1.
2.
2.
3.
3.
4.
4.
1.
2.
3.
BLEEDING
The MICO Open Center Power Brake
Valve and remaining brake system
are sometimes difficult to bleed. The
difficulty arises when the hydraulic
oil used does not flow easily through
lines and small holes by means of
gravity. Generally, to effectively
remove air, oil must be forced into
the brake valve master cylinder
cavity and the rest of the system.
CAUTION:
Manual and pressure bleeding are
two methods of bleeding a brake
system. MICO recommends using
one of these two methods of
bleeding the Open Center Power
Brake Valve and the rest of the brake
system.
Be sure brake valve
is installed properly
and brakes adjusted
correctly before
beginning bleeding
procedures. CAUTION:
Start engine and allow enough
time to pass for the system to
become filled and thoroughly
flushed with oil.
With engine still running, one
person can stroke the brake pedal
while another person opens and
closes the brake bleeder screws.
Only on the down stroke of the
brake pedal, open bleeder screw on the brake closest to brake
valve first. When all flow stops
from bleeder, close it and allow
pedal to return to rest.
Wait at least 30 seconds and
repeat the process until all air has
been expelled from that brake.
Then go on to the next closest
brake bleeder and repeat process
until all brakes have been bled. Stop engine and depress brake
pedal. Pedal should be hard, not
spongy, and fairly high. If pedal
is too spongy and/or travels too
far, repeat bleeding process.
It is a characteristic of the brake
valve to kick the pedal back when
actuated if system is not bled with
engine running.
MANUAL BLEEDING
PROCEDURES
4.
1.
2.
3.
5.
6.
(14)