02-19-2023, 10:50 AM
Very interesting information and a good reference as to the turning radius performance of the ZF RAS system (Rear Axle Steering).
In recent years, I have gained some additional knowledge of the ZF steering system both front and rear. There are components in the RAS system that can impact how the tag axle operates. One being the pressure accumulator. Based on information I received from the factory, the accumulator itself has a ten year lifespan.
The accumulator should also be serviced on an annual basis. I believe the service consists of checking the nitrogen pressure provided there is no system hydraulic fluid leak noted during service inspection. I believe 250 psi is used on my 2005 system.
If the accumulator nitrogen pressure leaks down the system may not operate as designed and impact operation especially when backing up. Backing and turning is impacted significantly, the tags can turn in the wrong direction due to the forces acting on the tires. The accumulator pressure also assists in keeping the tag hydraulic actuating cylinder centered while traveling straight down the road.
FYI - The ZF RAS system is a closed looped hydraulic system that is completely independent from the engine driven hydraulic system with one exception. The two hydraulic systems share a common part, the forward master cylinder.
BTW... Bosch is now the supplier of the ZF steering components.
In recent years, I have gained some additional knowledge of the ZF steering system both front and rear. There are components in the RAS system that can impact how the tag axle operates. One being the pressure accumulator. Based on information I received from the factory, the accumulator itself has a ten year lifespan.
The accumulator should also be serviced on an annual basis. I believe the service consists of checking the nitrogen pressure provided there is no system hydraulic fluid leak noted during service inspection. I believe 250 psi is used on my 2005 system.
If the accumulator nitrogen pressure leaks down the system may not operate as designed and impact operation especially when backing up. Backing and turning is impacted significantly, the tags can turn in the wrong direction due to the forces acting on the tires. The accumulator pressure also assists in keeping the tag hydraulic actuating cylinder centered while traveling straight down the road.
FYI - The ZF RAS system is a closed looped hydraulic system that is completely independent from the engine driven hydraulic system with one exception. The two hydraulic systems share a common part, the forward master cylinder.
BTW... Bosch is now the supplier of the ZF steering components.
Kristi & Jeff King
Bentonville, Arkansas
#744 2005 45’ Newell Coach
ZF Suspension/Active Steering Tag Axle
CAT-13 ACERT KCB Engine 525HP 1642 ftlbs Torque Cat Compound Turbocharger 43.5 psi
Allison HD4000MH Transmission with PTO drive.