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Page 84
TROUBLESHOOTING
ENGINE BRAKE ACTIVATES WITH SWITCHES
OPEN (OFF)
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Solenoid valve seal center ring
damaged — Remove solenoid and replace
all three seal rings.
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Engine brake improperly wired — Check
wiring in accordance with MACK wiring
diagrams.
ENGINE BRAKE SLOW TO OPERATE OR
WEAK IN EFFECT
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Lube oil cold and thick — Allow engine to
warm before operating brakes.
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Improper slave piston adjustment or
slave piston sticking in bore — Readjust
in accordance with the Table on page 80.
Ensure that the slave piston responds
smoothly to the reset screw by loosening the
jam nut and turning the screw through its full
travel for full slave piston motion. Make sure
piston travels the full range without binding
or sticking.
Remove the slave piston carefully when
disassembly is necessary. Use Jacobs slave
piston tool part No. 4559-25084. Slave piston
springs are under heavy compression.
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Reset screw not properly sealing —
Remove reset screw and check for debris on
the plunger or surface of the slave piston.
Check to ensure that plunger moves freely
with light pressure. Tip of plunger should be
smooth and free of nicks or scratches.
Replace reset screw if necessary.
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Lower solenoid seal damaged allowing
oil to exit the housing — Remove solenoid
valve and replace all seal rings.
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Solenoid screen clogged stopping
supply of oil to brake — Remove solenoid
valve and clean screen.
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Master piston not moving in bore —
Inspect master piston and bore for scoring or
burrs. If any are present, clean the surface
with crocus cloth. If unable to remove burrs,
replace piston or housing. Inspect lube oil for
signs of contaminants. If any are present,
replace oil and filter and correct cause of
contamination.
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Control valves binding in housing
bore — Remove control valve. If body is
scored, replace the control valve. Check for
contaminants in lube oil. Clean housing and
control valve. If binding continues, replace
housing.
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Control valve defective — Remove control
valve. Make sure check ball is seated in
bore and can be moved off seat. Make sure
there is spring pressure against the ball.
Flush in cleaning solvent. Replace if
necessary.
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Switch operation sluggish — Check dash
switches, clutch switch, or other control
switches. Readjust or replace as required.
Check clutch return springs for proper
operation. Check all controls for correct
operation and replace as required.
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Solenoid valve operation erratic — Check
solenoid valve using electrical specifications
presented in the Table on page 80.
Disconnect the solenoid lead and provide
12 volts directly to the solenoid. Ensure that
the solenoid cap depresses.
Do not touch electrical connection when
system is energized.
OIL PRESSURE DROPPING BELOW MINIMUM
REQUIRED FOR ENGINE BRAKE OPERATION
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Upper solenoid seal ring damaged —
Remove solenoid. Inspect seal ring and
replace all seal rings.
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Aeration of lubricating oil — Check for
aeration of the oil. Activate, then deactivate
engine brake and observe escape oil
coming from control valve cover. If oil has
bubbles or is foamy, air is present in system.
Aeration can be caused by an overfilled or
underfilled crankcase, or a crack or other
leak in the oil pickup tube. Correct in
accordance with MACK procedures.
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Lubricating oil being diluted by fuel oil —
Have an oil analysis of lube oil to determine
if fuel is present. Correct per MACK
procedures.
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Low engine oil level — Consult engine
manual for specifications. Add oil or
recalibrate dipstick as required.
5_106_00.bk Page 84 Friday, August 4, 2000 11:17 AM
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