A heavy duty auxiliary transmission or transfer box shall be
220.127.116.11.1 Auxiliary Transmission.
provided to direct the power to the front and rear axles. The unit may incorporate torque multiplication.
This unit shall contain an inter-axle differential of a torque proportioning type if constant 4-wheel drive
is supplied, if selective 4 wheel drive is supplied no differential is required. The functions of this unit
may be included in the transmission. The auxiliary transmission must meet the same rating criteria as
The load rating of each axle shall be not less than the imposed load on the axle,
measured at the ground, with the vehicle at gross weight. The axles shall be interchangeable with the
changing of steering linkages and brake systems. The axle shall be equipped for steering and shall
incorporate a torque proportioning differential with a bias ratio of not less than five to one or a limited slip
differential. The axles shall be planetary final drive type.
Steering system. The steering system shall be hydraulic power boosted with a mechanical
linkage (or equivalent). The vehicle shall be capable of passing the tests in SAE J53. The tractor shall
furnish three modes of steering, two wheel, four wheel coordinated and four wheel oblique (crabbing). The
change of mode shall be accomplished by the movement of one hand operated handle while the vehicle is in
motion. The tractor shall remain in the selected mode until a new mode is selected by the operator. A
capability for small increments of forward and reverse movement is required. When switching from
crab or coordinated to the two wheel mode of steering, the rear wheels shall automatically center (wheel
perpendicular to axle) without operator input or adjustment. Two wheeled steering mode shall function up
to governed speed while turning in four wheel drive without any axle bind. The static vehicle, at idle, in
four wheel steer mode, shall be capable of steering from extreme left to extreme right in a maximum of
five seconds in accordance with Figure 8 of MIL-STD-1472. The steering fluid dipstick shall be accessible
without removing panels and shall not subject personnel to burns or excessive reaching.
18.104.22.168 Steering wheel. The steering wheel shall have a diameter of 18 inches minimum. Not less
than four inches clearance shall be provided between the steering wheel rim and the nearest projection in
the plane of the steering wheel. No less than 2 1/2 inches clearance shall be provided between the steering
wheel rim and the nearest projection below the steering wheel.
If electronic steer is used, the following shall be met.
22.214.171.124.1 Steering lockout.
In the case of any broken wheel potentiometer wire(s), the steering control
system shall be locked out, leaving the rear wheels in the position they were in when the failure occurred.
An alarm audible from inside and outside of the cab shall sound when the steering
lockout is activated. This alarm shall be de-energized when the tractor ignition switch is turned off, but
shall be re-energized should the ignition switch be turned on again prior to manually resetting the
126.96.36.199.3 Lockout indicator lights. A steering lockout indicator light located on the instrument panel
shall be energized when the steering lockout is activated. A nameplate explaining what the operator
should do in this situation shall be mounted next to the light. This Light shall be de-energized when the
tractor ignition switch is turned off, but shall be re-energized should the ignition switch be turned on
again prior to manually resetting the system.
188.8.131.52.4 Manual rear wheel positioning.
The capability shall exist for the operator in the cab to
manually position the rear wheels in the case of rear wheel steer lockout. This capability shall allow the
operator to complete the current run and return the tractor for maintenance.
184.108.40.206.5 Trouble shooting lights. Trouble shooting lights, easily accessible by maintenance personnel,
shall indicate whether the broken wire(s) is in the front or rear wheel potentiometer circuit. These lights
shall remain energized until maintenance personnel manually reset the system. The system shall be
reset by pressing a reset button or switch. The trouble shooting lights shall remain energized even with the
tractor ignition in the "off' position.