5540F/YB5515 SERVICE MANUAL
9-8 Published 10-21-2010, Control# 198-04
1. With the engine shut off and the parking brake engaged,
close the accumulator needle valve Figure 9-11 to shut
off hydraulic pressure to the service brakes.
2. Actuate the brake foot pedal until no resistance is felt
and the system pressure has been released.
NOTE: Do not disconnect any lines until the brake circuit
pressure has been released.
3. Remove and cap the brake piston feed line A
Figure 9-12.
4. To check for severe piston seal damage:
a. Fill the housing of hand pump with Mobil fluid 424,
or equivalent hydraulic oil.
b. Install the hand pump fitted with a 0 to 1000 psi (0 to
6890 kPa) pressure gauge to port B Figure 9-10.
NOTE: The hand pump MUST be filled with Mobil fluid 424
or equivalent hydraulic oil. System pressure is
550 psi (3790 kPa) DO NOT exceed 600 psi.
(4134 kPa).
c. Use the hand pump to generate a pressure in the
brake piston housing.
d. If the pressure falls off rapidly, or if no pressure
reading can be obtained, the seals are severely
damaged and must be replaced.
5. If pressure falls off slowly, the piston seals may have
small cuts or nicks. To verify for small cuts or nicks in the
piston seals perform the following test:
a. Install an adapter fitted with a piece of clear tube
(approximately 4.75 in (120 mm) long to the brake
piston port B Figure 9-13.
NOTE: The tube must be kept vertical during the test. Use
tape to attach the tube to the side of machine.
b. Fill the tube until is approximately three quarters full
with Mobil fluid 424 or equivalent hydraulic oil.
FIGURE 9-11
p1871
Accumulator
Needle Valve
Reference Only
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