JLG T500J Service And Maintenance Manual page 68

SECTION 3 - CHASSIS & TURNTABLE
IF THE INDICATOR IS IN THE RED "-" ZONE, THE COUPLING IS NOT PROPERLY
CLOSED, AND THE TRAILER MUST NOT BE TOWED!
There are three possible causes of this problem:
1. The ball on the towing vehicle is very worn down and
the ball coupler cannot grip it properly. A new ball has a
diameter of 50.0 mm. If the diameter is worn down to
less than 49 mm, even if only in places, it is vital to
replace the ball on the towing vehicle.
2. The ball coupler itself is very worn down and no longer
grips the ball sufficiently. In this case, the ball coupler
must be replaced at a qualified workshop.
3. The closing mechanism in the ball coupler has been trig-
gered, but there is no ball in the coupling. The ball cou-
pler is only lying loose on the ball and is not firmly
connected. The coupling will separate from the ball
when the towing vehicle drives off. Open the coupling
as described earlier and try once more to click the ball
coupler correctly into place on the ball.
The coupling mechanism may be stiff due to insufficient
lubrication. Carry out the instructions for maintenance
and lubrication and try the coupling procedure again.
PERMISSIBLE SUPPORT LOAD
The support load permitted for each particular ball coupler is
embossed on the hand lever of the ball coupler.
NEVER DRIVE WITH A NEGATIVE SUPPORT LOAD AS THIS WILL HAVE A NEGA-
TIVE EFFECT ON THE TRAILER'S DRIVING STABILITY.
A negative support load can be avoided or remedied simply
by changing the trailer's load.
POSITION OF THE COUPLING POINT ON THE TRAILER
TO ACHIEVE THE CORRECT DRIVING AND BRAKING BEHAVIOR IN THE TRAILER,
IT IS ABSOLUTELY ESSENTIAL FOR THE COUPLING HEIGHTS OF THE TOWING
VEHICLE AND THE TRAILER TO MATCH.
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The position of the coupling point on the trailer must be in a
range of 430 ± 35 mm above the horizontal tire contact sur-
face.
To check the coupling height, the trailer and towing vehicle
must be exactly horizontal and fully loaded to make up the
permissible total weight. The tire pressure must also conform
with the tire manufacturer's specifications.
BALL COUPLER MAINTENANCE
To ensure easy operation and safety, all bolts and movable
parts of the ball coupler must be lubricated using commonly
available machine oils, or as a substitute, motor oil twice a
year, or immediately if the coupling becomes stiff.
The ball mount should also be lightly greased, with the excep-
tion of all stabilizer couplings.
The bolts fastening the coupler to the adapter should be
torqued to 85 ft.lbs. (115 Nm).
OVER-RUN HITCH MAINTENANCE
Relubricate the over-run hitch after 3000 miles (5000 km) or
after one year at the latest, at both grease fittings. All movable
parts such as bolts and articulating points on the hand brake
lever and the turning lever must also be lightly oiled.
If the connecting rod can be pushed in more than half-way
(approx. 45 mm) when the hand brake is on, the braking sys-
tem must be readjusted.
Check the brake response:
1. Put the handbrake on while the trailer is uncoupled and
push the trailer slowly backwards until the handbrake
lever has reached the hindmost end position.
2. Push the ball coupler/connecting rod into the over-run
hitch. Depending on the over-run hitch, it will require a
certain amount of force to push.
3. The connecting rod should then return automatically to
zero position by means of the gas cushion in the hydrau-
lic damper. If it takes longer than approximately 30 sec-
onds to return, the over-run hitch must be checked at a
qualified workshop.
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