TROUBLESHOOTING
Page 117
ONE OR MORE CYLINDERS FAIL TO STOP
BRAKING OR ENGINE STALLS
앫 Control piston spring/valve inner spring
broken — Replace piston spring.
앫 One or more control pistons/valves stuck
in ON or UP position — Check control
pistons/valves for binding. Remove and
clean, or replace if necessary. Inspect lube
oil for contaminants.
앫 Lower solenoid O-ring damaged (allows
oil to enter brake with solenoid valve
closed) — Remove solenoid and replace all
O-rings.
앫 Solenoid valve exhaust plugged —
Remove any restrictions at exhaust (bottom)
of solenoid valve.
앫 Clutch switch stuck in ON position or out
of adjustment — Check for proper
operation. Readjust or replace as needed.
ENGINE MISSES OR LOSES POWER
앫 Hydraulic actuator adjustment too
tight — Readjust engine brake lash in
accordance with the table on page 114.
SUDDEN DROP IN ENGINE LUBE OIL
PRESSURE
앫 Upper solenoid valve seal missing or
damaged — Remove solenoid and replace
upper seal ring.
Removal and Inspection of MACK
PowerLeash™ Engine Brake
Components
INSPECTION
If oil pressure to the rocker shaft is not sufficient
for engine brake operation, inspect the oil supply
screen in the bottom of the front rocker shaft
mounting bracket for debris, and clean or replace
as necessary.
If oil pressure at the rocker shafts is sufficient for
engine brake operation, then inspect the engine
brake hydraulic actuator components for excess
wear or damage.
1. Remove the retaining ring that holds the
control piston cap in place on top of the
actuator. Remove and inspect the control
piston and spring. Free length of the spring
should be 0.955 inch (24.3 mm). If the spring
is broken or the free length is not within
specifications, replace the spring.
2. Check the control piston for freedom of
movement in the actuator bore. The control
piston must move freely. If the piston binds
or sticks, or if there are burrs on the piston or
in the bore or if there is evidence of scuffing,
replace the piston. Check the pintle on the
end of the piston and replace if broken or
showing evidence of wear.
103
Figure 103 — Check Control Piston Spring Free-Length
and Pintle Wear
1. Inspect Pintle for Wear or
Damage
2. Snap Ring
3. Cover
4. Spring
5. Control Piston
5-111.bk Page 117 Monday, July 10, 2006 2:26 PM
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