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Full Version: ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098
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I’ve collected the following information using the ZF Data Plates on our 2005. The coach was built in 2004 as unit #744. I have no idea how long Newell used the ZF RL-85 suspension and drive train. The Drive Axle has a different designation (A-132/S-91/PP 476774).

Steer Axle Data Plates were located on the left and right steering hubs. 
Steer Tag Axle Data Plate was located on the aft side of the horizontal beam, left of centerline. 
Drive Axle Data Plate was located on the left driveshaft tube facing aft. The differential has its own data plate mounted on the housing.

Data plates may be difficult to see due road grime, they may have been covered by tape when the undercarriage was painted black. I used simple green HD to clean off the areas where the data plates are mounted. Note: Simple Green HD should not corroded metal parts. 

I worked with ZF technical customer service to identify the part numbers listed below. They provided me with diagrams and parts list which I’m also posting. ZF is a enormous German company that manufactures and supplies several lines of motor vehicle equipment. Maneuvering within their system is at first overwhelming and frustrating. I have requested from ZF availability and prices for the parts listed below. I will update information as it becomes available. 

Steer RL-85/E

Drive Axle A-132/S-91/PP

Steer Tag Axle RL-85/A

Steer Tag Axle Function, Maintenance, Inspection, Troubleshooting  

Steering Gearbox 8098

The following document covers several different types of ZF Servocom systems including the RAS, REAR AXLE STEERING. I urge every ZF owner to study the system so you have a solid understanding how your Active Steerable Tag system functions. It requires ANNUAL inspections and maintenance. There is a pressure accumulator that should be served annually and replaced after 10 years of service. 
Pressure accumulators in the ZF RAS look like a small metal soccer ball mounted in the frame between the drive and tag axle. The accumulator is pressurized with nitrogen and works in conjunction with the RAS closed loop hydraulic system pressurized to 250 psi. 
The nitrogen side of the accumulator can experience micro leaking of the valves used for testing and servicing. If the pressure in your tag system is not correct you may experience anomalies during operation. There is a pressure sensor installed in the system that is activated at or below 230 psi and turns a light on at the drivers position warning of low pressure situation. 
Low pressure in a tag system will manifest while backing up and the tag tires my not move in the correct direction. If the tag pressure is low enough the tires will turn in the wrong direction and backing up is impossible. Don’t force it! 

Steering Systems and Accessories for Commercial Vehicles

These are life limited parts steer axle and tag axle steer system. There may be additional parts such as steer axle hub bearings for the control arms. 

Steering Axle Tie rod Part # 0501.007.768 (one required)
Steering Axle Tie rod Part # 0501.007.769 (one required)
Steering Axle Tie rod Part # 0501.007.611 (sway bar link-two required)
Control arm bushing Part # 0501.314.963 (eight require)

Sway Bar Link Assembly - LEMFÖRDER 3079901

Steering Tag Axle Tie rod Part # 0501.005.797 (one required) 

I have not identified tie rod ends for the steer gearbox hydraulic assist system. 
I have not identified tie rod ends for the steer tag axle hydraulic actuator.

These documents provide a wealth of information about the ZF suspension. 
Lubrication and Maintenance 

Operating Manual

Repair Manual

Time in service is a limiting factor in these steering parts. Keep in mind the coach may have low mileage but time is an enemy to any of these parts. They live in a hostile environment far below the driver’s seat. The tie rod ends have rubber boots designed to protect the inner workings of these parts. If the boot is damaged in any way, the world of road grime and nature’s elements have an open door to enter and degrade the performance of these critical steering parts.
Greetings all.

Today I added ZF documents to my original post that include information about the steering gearbox, steerable tag axle diagrams, maintenance, and troubleshooting. I continue to gather data and information that will be valuable to owners of the early ZF suspensions and steerable tag axle. 

Take care, 
TX for the info!
@jdkskyking, thanks for sharing.
Could you elaborate a bit more info on the steering tag pressure accumulator? The location on the coach and perhaps some photos?
The steering tag system is a closed loop system pressurized to 250 psi in conjunction with a pressure accumulator.  The accumulator has a ten year life span, the pressure should be checked annually. There is also a 230 psi pressure sensor mounted in a hydraulic block that turns on a light at the drivers warning panel.
The accumulator is mounted up high between the drive and tag axels. 
The system incorporates two actuators, the rear is the slave and can easily be seen by looking between the drive and tag tires. The forward actuator is a combination unit that also serves as the steering assist actuator but the two hydraulic systems are separate. The steering tag system is stand alone and does not use the engine driven hydraulic system. 

Hello again,

Here’s what I do on Thanksgiving…

Carve stuff up to see how it works. This is the ZF Servocom RAS “Master Cylinder”.

This cylinder and its center section is responsible for controlling the Steering Tag Axle. 






I see you cut the cylinder. Did you then see what was preventing the rod from coming out?
I haven’t had time to study it. I’m sure there’s a assembly trick that gets reversed with special tools. Look at pic 2 & 3, there are collars that fit in the channel in the rod held in place by a O ring.
I‘ve requested the ZF manual for Master and Centering Cylinder.
When I have time I’ll see what makes the center section tick.
More pics to come.
My journey continues. I’ve learned more about the steering and suspension on 744 than I care to admit. Subject matter expert??? Possibly or very close. One day when I’m done I’ll summarize everything I know so others can benefit. 

Most recently the subject is suspension bearings or better yet, drive axle and tax axle control arms which contain the rubber bearings. 

I ordered every suspension bearing under the bus. Eight for the steering axle control/A arms and eight for the rear. 

These are the steer axle bearing. They press into the upper and lower control arms then bolt to the coach frame. 

These pics are a small selection of my installation of the TAG Axle control arm replacement and Drive Axle. Each axle has four arms each. My bone pile has grown, I’m down to two control arms, drive axle uppers. 

ZF Part numbers for rubber bearings and complete control arm assemblies for the drive axle and tag axle.

The steering axle control arm bearings are all the same, eight total. A press is required to remove and reinstall the bearings. 

The drive axle control arms are different lengths upper and lower. The upper are the longer. 

The four tag axle control arms are the same length. 

0501.314.963 Rubber Bearing-Steer Axle Upper/Lower Control Arm (eight total).

0501.222.516 Tag Axle Control Arm Assembly 

0501.222.518 Drive Axle Control Arm Assembly  
0501.222.517 Drive Axle Control Arm Assembly

This is a sampling. Some day I’ll write up the details and provide all the ZF part numbers. 

Essentially I’m zero timing the suspension. 

Take care,
Jeff, you got my attention with the statement that he accumulator has a 10 year life, that's where 1482 is since it was manufactured in 2012.  I see another project for this winter figuring out what is needed.  Do you know offhand if there have been any/many changes in the system from yours to mine?  Are you finding the "O" rings in good condition when you remove them?  Also, is your maintenance due to leaks, mileage or preventative?  Where are you acquiring parts from?

Your data is outstanding and will be an immense help for all of us that will go down that rabbit hole.
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