The Z.F. Steering Gear is a semi-integral power
against axial thrust by means of two anti-friction
steering unit that directs the steering fluid to the steer
bearings. The control valve is installed across in the
cylinders in response to the movement of the
piston. The valve is composed of a valve spool and
steering wheel. The steering housing contains the
two fixed reaction pistons. One finger of the steering
control valve, a complete mechanical steering gear,
nut fits snugly into the bore of the valve spool. The
and it is at the same time the operating cylinder of
piston and the sector shaft are positively connected
the piston. The worm and the steering nut are
by a gearing. Due to a special tooth shape on the
connected by an endless chain of balls. The balls
sector shaft, their axial adjustment is possible. This
are returned via a recirculating tube. The steering
ensures clearance free operation in the straight
ahead travel range.
THEORY OF OPERATION
In the neutral position of the valve, the oil pressure in
Consequently the oil pressure is now supplied to
the right and the left cylinder chambers is balanced.
only one of the two cylinder chambers. The piston
By moving the valve spool from the neutral position,
assists the worm rotation. A compression spring
a pressure difference is produced between the left
arranged in the steering nut causes the return of the
and the right cylinder chambers. The piston will
steering nut, and also the valve spools, to neutral
receive more oil pressure on one side, and the
position. The return to neutral, is also assisted by a
hydraulic power assistance is operative. The valve
design function called hydraulic reaction.
is actuated by a rotation of the steering wheel, or by
hydraulic pistons are mounted to float in bores of the
the forces which coming from the road wheels, act
valve spool, and secured against axial movement by
through the sector shaft and piston on the steering
locking plates. The outside faces of the two reaction
nut and worm. Any rotation of the worm means an
pistons are permanently pressurized in the operating
axial movement of the piston, and a radial movement
position of the valve. Likewise only one of the two
of the output shaft. This operation causes the valve
faces in the bores of the valve spool are pressurized
spools to be moved by the finger on the steering nut.
with oil. This causes a hydraulic reaction force which
is trying to return the valve spool to the neutral
Remove the nut, bolt, and washer securing the
relay shaft to the steering gear.
Tag and disconnect the hydraulic lines to the
steering gear. Cap or plug all lines and openings.
Remove the bolts and washers mounting the
steering gear to the mounting bracket on the carrier
Disconnect the drop arm from the steering
frame. Remove the steering gear.