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ZF Suspension-RL-85/E and RL85/A Steerable Tag Diagram/Steering Gearbox 8098
#11

Mine is the early version. I’d imagine yours has the shocks with feedback or even lowers at highway speed? I’m not familiar with the evolution. 

I would imagine the ZF RAS is similar, you probably have 365 on the tag. Not sure how that changes things but the principle is the same. I believe I have uploaded the documents that explain how it works. I know there is a ZF 7.5 ton system and a 9 ton version. 

The nuts and bolts of my situation, I lost the nitrogen pressure in the accumulator, that allows the rear of the coach to sway back and forth because the rear CENTERING CYLINDER needs the pressure to hold the tags straight going down the road. Crack the whip with my Gladiator in tow. I am of the opinion that I drove it that way long enough to shorten the life expectancy of the bushings. I had a tag bushing that was comprised. This week I found a drive bushing in a similar state. They’re keeping a lot of weight in check back there. 

This entire experience was more “discovery” than anything as I was apparently the first to bring this to the attention of the Newell Service Department. The manager told me about the service life, annual inspection/servicing, adding the accumulator to the PMI, and that they now stock the accumulator. 

My anal retentive tendency and high expectations is why I decided to essentially zero time the suspension. Newell and I replaced almost every single component of the ZF Rear Axle Steering System because we were understanding ever we were dealing with. I contacted a German company with extensive ZF RAS experience and was given valuable information. I’m not done yet. 

You should have a pressure sensor on the tag accumulator system that will alert you to a low pressure situation. My sensor was also inoperative. How unusual. 

Besides my coach driving like crap, the true first symptom was while backing up, the tags turned in the wrong direction. 

If EVERYTHING is setup properly, good system. If not, potential problems. 

I just read a FB post about rubber smell in the tow vehicle. I had the same. Thought it was my Jeep tires. It was the drive tires going in one direction and the tags going in another. Scrubbing. Ruined a new set of tags on a trip because of it. 
It as a problem “synchronizing” the the two hydraulic cylinders in the system AND the all wheel alignment. The new service manager Dusty got the alignment rack in order with a new third party tech to ensure the rack is calibrated properly. Mine was completely out of tolerances for various reasons. 

Two more drive axle control arms and the rear is done. I’ll get to the steers when I figure out a way to change the bearings without completely removing the steer A arms. 

Like I said, then the icing on the cake but I’ll document that after I’ve accomplished it and validated the reason for it. 

JK

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.
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#12

Newell just finished replacing all eight airbags with new ZF airbags. 

   

When Newell removed the drive tires they found a cracked rotor and brake pads destroyed. 

   

   

My advice is to pay to have the tires removed and visually inspect and measure rotor and pad thickness.


I requested that an alignment be completed since I replaced all eight control arm/bushings for the drive and tag axles. 

During the process the tag axle hydraulic pressure was check. Gauge indicated 150 psi. 100 psi low! I DID NOT HAVE A TAG AXLE INDICATOR AT THE DRIVER POSITION. 
The pressure sensor had also failed. That’s two failed sensors on my coach since I’ve owned it. In theory, when the pressure in the ZF RAS drops below 230 psi, a warning light should illuminate at the driver annunciator panel.

We noticed two of the hydraulic lines that connect the REAR CENTERING CYLINDER to the rear ZF RAS  HYDRAULIC BLOCK were wet. We replaced all four lines with a high quality line. Cost was $150 at a local Miami OK shop Newell uses. 

   

Newell has decided to increase the ZF RAS hydraulic pressure to 275 psi. 
I’m in the process of determine what the accumulator nitrogen charge should be set to. 


As a reminder, I was told that the ZF RAS pressure accumulator has a 10 year lifespan and the system pressures should be checked annually. 

I certainly hope to continue to increase my knowledge on the ZF suspension system and work to keep owners informed. 

JK

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.
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#13

Nice write-up on the ZF suspension.  These things are a different animal for sure.

Rob
2016 Newell #1536

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