24
T
ROUBLE
“A”
CONTINUED
FROM
P
REVIOUS
P
AGE
5. The ABS brake may not release as a
result of damaged internal compo-
nents.
6. The ABS brake may not be releasing
due to an incorrect or no pilot pres-
sure signal.
7. The ABS brake may not be releasing
properly due to incorrect free flow
check valve pressure within the brake
valve.
C. Apply 800 PSI (5,500 kPa) to the
ABS release port. Check the cable drum
to determine if it spins freely. If it does
not, slowly increase the pressure until
the drum is free.
DO NOT
exceed 1,200
PSI (8,300 kPa) in this port.
D. If the ABS brake assembly will not
hold pressure, the brake assembly must
be disassembled and inspected or
repaired, as defined in "Auxiliary Brake
Service".
Disassemble the brake to inspect the
internal parts. Refer to "Auxiliary Brake
Service" for further information.
Check the ABS brake release pilot pres-
sure as follows:
A. Install an accurate 0-2000 PSI (0-
13,800 kPa) pressure gauge to the ABS
release line between the hose and port
fitting.
B. Remove the shuttle valve from the
inlet port (Port 2) of the pressure reduc-
ing valve body.
C. Attach a hand pump with an accurate
0-2000 PSI (0-13,800 kPa) pressure
gauge to the inlet port of the valve body.
Apply 1000 PSI (6,900 kPa) to the valve,
and record the pressure on the ABS port
gauge. Adjust the pressure reducing
valve, as required, to attain 1000 PSI
(6,900 kPa) on the ABS port gauge. If
the correct pressure cannot be reached,
the pressure reducing valve cartridge
should be replaced.
The free flow check valve within the
brake valve should open fully at approx-
imately 400 PSI. If an incorrect or weak
spring is present, the check valve can
open early allowing scrubbing in the ABS
brake. Replace the spring or check pop-
pet as needed.
TROUBLE
PROBABLE CAUSE
REMEDY