IMPORTANT INFORMATION FOR DRIVER
ZF Power Steering Gears which are installed according to instructions, expertly maintained and
operated free of accidents will attain a long life. To obtain full functional capacity, we recommend a
checkup of all mechanical steering components (visual check of all and a crack test of highly
stressed parts as well as an exchange of seals and gaskets within scope of 3rd inspection (refer to
The size of the steering system and the mechanical steering ratio are selected in cooperation with
the manufacturer of the respective vehicle in such a manner that in the event of a failing hydraulic
steering support (power steering) the max actuating forces to be applied at steering wheel will not
exceed a maximum extent considered reasonable by pertinent legislation.
This force is 600 N at the circumference of the steering wheel when the car, traveling straight
ahead, is turned into a circle with a 12 m radius (BO-circle - FRG- specific). At a road speed of
approx. 10 km/h, the requisite lock should be applied within 6 seconds at the most, or 8 seconds in
the case of vehicles having a design-related maximum speed of 25 km/h. The driver must be aware
that should the hydraulic assistance suddenly fail, due to the failure of the pump drive, for example,
the vehicle will still be steerable although considerably more force will be necessary to turn the
steering wheel. Since situations of this nature are extremely rare and generally give no prior
warning of their occurrence, the driver may mistakenly assume that the steering system is locked.
However, this is not the case. The driver need only apply the requisite force to steer the vehicle.
Single-circuit steering systems which require the application of a force in excess of 600 N to steer
the aforementioned BO-circle in the event of the hydraulic assistance failing are equipped with an
engine-independent back-up emergency steering pump.
This important information is intended to serve general safety and should be of assistance to clarify
interrelations as described above to protect the driver against erroneous assumptions in such a