Mercedes-Benz M-Class 2012 Owners Manual - Manual (Page 215)

correct installation and torque at a qualified
specialist workshop.
G WARNING
The ball coupling can be damaged if the nut is
tightened on the ball coupling with the
incorrect torque. This could cause the trailer
to detach while driving and an accident could
occur as a result.
Therefore, please observe the following:
R do not exceed the maximum permitted
noseweight of the ball coupling, the trailer
coupling and the trailer tow hitch.
R when installing, always use a retaining ring
between the nut and the mounting surface
of the ball coupling carrier.
R if the assembled ball coupling has been
permanently mounted on the vehicle, have
the ball coupling regularly checked for
correct installation and torque at a qualified
specialist workshop.
R check that the thread under the nut is of
the correct length.
! Mercedes-Benz recommends that you
only use ball couplings tested and
approved for use on Mercedes-Benz
vehicles. This helps to avoid damage to the
vehicle.
Observe the manufacturer's installation
instructions if you use a ball coupling other
than the one supplied.
i Also observe the height of the trailer
coupling and the trailer manufacturer's
instructions.
i Depending on the height of the trailer
coupling, it is possible that the ball coupling
will have to be rotated by 180° on the ball
coupling carrier for correct installation. The
assembly is otherwise identical.
X Insert ball coupling : through the hole in
ball coupling carrier ; as far as it will go.
X Slide retaining ring ? onto the thread of
ball coupling = as far as it will go.
X Screw on nut A as tightly as possible.
X With a torque wrench, tighten nut B to a
torque of 516 lb-ft (700 Nm).
X Check that projecting thread C has the
requisite length of 0.32 in (8 mm) beneath
nut B.
X
Check the assembled ball coupling for
correct installation.
Trailer towing
213
Driving
and
parking
Z