[jdkskyking]

It is very important to have the ZF RAS (Rear Axle Steering) hydraulic system inspected and serviced. Make sure to keep an eye on your four hydraulic lines connected to the Rear Centering Cylinder. I replaced all four of mine when I picked up the coach from service work recently. The four hydraulic lines are exposed to road debris and the elements. The hydraulic lines that were replaced were wet and collected debris. 

HYDAC makes a pressure gauge that attaches directly to the nitrogen valve on the bottle. I’m trying to find out more information about the gauge unit. 

The accumulator is pre-charged to approximately 150 psi with nitrogen. The hydraulic side of the system is then pressurized to between 250 and 275 psi. 
If your system is weeping fluid like mine apparently did, the system pressure will decrease. 

In 2021 I had a complete accumulator and hydraulic pressure failure. The coach could not be backed up because the system pressure holds the TAG axle straight as we backup until the steering axle system moves beyond 5° of center. In my experience, the TAG tires will move in one direction or the other based on forces of the road surface. Mine moved in the same direction as the steer tires and the coach stopped moving. 

And to answer your next question… you can drive forward because of the TAG Axle Caster but it will likely handle poorly as the TAG Tires can move slightly left or right. 


Accumulator Data I recorded from a new unit. 

Manufacturer:
HYDAC 66280 
Made in Germany 

(Part Numbers)
02112867/663/010
BOSCH 3591.005.099

Pre-Charge of 10 BAR (145 psi)

V 2L 

PS 40 BAR
PT 143 BAR

TS-40/80° C 

As usual information about the accumulator is difficult to find. If anyone can decode the above information please post. 

Keep an eye on your TAG Tire sidewalls for unusual scrubbing which could be a symptom of low ZF RAS hydraulic pressure.

More to come… 
JK