JLG T350 Service Manual - Manual (Page 54)

SECTION 3 - CHASSIS & TURNTABLE
3-18 – JLG Lift – 3121198
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 lon-
ger 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
triggered, but there is no ball in the coupling. The
ball coupler 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 insuffi-
cient lubrication. Carry out the instructions for main-
tenance 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 NEGATIVE EFFECT ON THE TRAILER’S DRIVING STABIL-
ITY.
A negative support load can be avoided or remedied sim-
ply 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 COU-
PLING HEIGHTS OF THE TOWING VEHICLE AND THE TRAILER TO
MATCH.
The position of the coupling point on the trailer must be in
a range of 430 ± 35 mm above the horizontal tire contact
surface.
To check the coupling height, the trailer and towing vehi-
cle 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 mov-
able 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
exception 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
system 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 hand-
brake 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
hydraulic damper. If it takes longer than approxi-
mately 30 seconds to return, the over-run hitch must
be checked at a qualified workshop.