TROUBLESHOOTING
Page 125
앫 Brake slave piston lash not properly
adjusted — The J-Tech™ model 690
engine brake units are very sensitive to
adjustment. Incorrect adjustment may hold
the valves open during positive power,
leading to engine failure, or may cause the
engine brake to work poorly or not at all.
Confirm that the engine brake is properly
adjusted in accordance with the table on
page 122.
ENGINE BRAKE DOES NOT OPERATE AT
LOW ENGINE RPM
앫 Inlet check valve leaking — Early
production engine brake housings contained
a check valve (with ball, spring, retaining
ring and washer) assembled into the
housing. In June 2000, the housing’s
internal check valve components and hollow
oil supply screw were replaced by a new oil
supply screw containing an integral check
valve. If the housing contains the early
production internal check valve components
and a hollow oil supply screw, remove the
check valve components (ball, spring,
retaining ring and washer) from the housing
and replace the hollow oil supply screw with
the current-production screw containing an
integral check valve.
ENGINE BRAKE ACTIVATES WITH
SWITCHES OPEN (OFF)
앫 Solenoid valve seal center ring
damaged — Remove solenoid and replace
seal rings.
앫 Engine brake improperly wired — Check
wiring in accordance with MACK wiring
diagrams.
앫 Solenoid not fully seated in rocker shaft
bore — Remove the solenoid, inspect and
replace the O-rings as required. Reinstall
the solenoid to its full seated position before
snapping the retaining spring clips in place.
The clips must require a moderate force to
snap them around the rocker shaft and must
provide enough spring tension to prevent
any free movement of the solenoid or spring
clips. If spring clip tension cannot be
maintained, replace the clips.
ENGINE BRAKE SLOW TO OPERATE OR
WEAK IN EFFECT
앫 Lube oil cold and thick — Allow engine to
warm before operating engine brake.
앫 Improper slave piston adjustment or
slave piston sticking in bore — Readjust
in accordance with the table on page 122.
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.
앫 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.
앫 Solenoid screen clogged stopping
supply of oil to brake — Remove solenoid
valve and clean screen.
앫 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.
앫 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.
앫 Control valve defective — Remove control
valve. Make sure check ball is seated in
bore and can be moved off the seat. Make
sure there is spring pressure against the
ball. Flush in cleaning solvent. Replace if
necessary.
5-111.bk Page 125 Monday, July 10, 2006 2:26 PM
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