[orbit1957]

Well here we go. This is a critical potential hydraulic emergency notification for the early steerable tag crowd. 

I'll do my best to convey the problem and yes, it is of DOT importance.  

1. Symptoms
2. Troubleshooting
3. Cause
4. Cure
5. Conclusion

1. SYMPTOMS

 Started out on a summertime trip looking forward to a relaxing get away.  As most of us know the relaxing part may or may not happen based on the rigs behavier. Three miles from home I start merging on the highway. 1 mile later I scan my instruments and I see I'm overheating. Pull over on the shoulder, leave the rig running and head to the rear.  The cooling fan not running.  First thing, I pull the connector on the manifold, still no fan. 

 I did install the fan overide cockpit controlled switch, or if adopted, in the official Newell Gurus Glossery, the FOCS.  Installing FOCS, IMO, is one of the best modifications to have in order to have some control for engine temp. Heat kills and so does my X wife when she feels the need.

Where were we? ADHD MOMENT.

 She's running around 215 degrees so I milk it to the next exit 1 mile away.  So since the fan is not working properly it's time to put my aviation skills to work. Check the hydraulic and coolant fluid levels, they are normal. Next I get my ball peen hammer and gently tap the manifold lightly repeatedly. Low and behold as I tap and the fan comes alive slowly. The more I tap the faster the fan responds. Within 20 secounds the monster is alive and spinning like she should. All is well so let's roll again and see how the temp is.  The temp stayed around 184ish so I feel comforitable and safe operationally. So I drove it this way for the excursion. 

2. TROUBLESHOOTING

Obviosly it first appears we have a spool valve that is not porting fluid properly within the manifold.  First step is to pull it out for examination. Suprisingly the fluid loss was minor when I pulled it out. Maybe 10oz but not much more. I examined the spool valve and orings and don't see anything that makes my eyes bug out. Next I put my finger inside the valve like a prostrate exam. There is someting in there so I keep examing the patient. The first piece I get out is a piece of metal and the 2nd 3rd and 4th piece are too.  This has to be the culprit but what the heck is it? The next move I reassemble what appears to be a big washer with an orifice drilled hole. They all fit together nicely, see pics.

It appeared that this was made intentioinally but for what purpose and where does it belong?  Time to call Newell on the bat phone.  I should have written down the names of the factory guys because without their knowledge this condition would forever keep me up at night. 

3. Cause
The pics of this washer orifice was uploaded and they said they would get back to me.  Maybe 15 minutes later I'm back live with the boys.  The guy they get gives me the Paul Harvey story. So Paul says, he remembers the issue, he goes back in time when they first encountered a pulsation after they installed the ZF tag.  He said when they first started with the steerable ZF tag there was a steering wheel pulsation that developed. 

4. Cure
Someone thought trying to reduce it by limiting the fluid flow and effectively dampening it. There was born the washer with a hole in it for the fix. Well it worked but in my opinion the fix was not properly done. I have worked on many hydraulic systems that use restriction orifices that either were bored out to a design specification in the manifold itself. Another method is to utilize a orifice fitting threaded into the manifold itself. Either way is considered a properly approved design or device. The washer was OK if it was used for developing a fix, but only temporary prototype testing.  Someone at Newell felt otherwise and used the homemade washer orifice as the cheap fix.

Anyhow, he asked if I had any pulsation issues with the steering wheel and I said I did not have any. He said, as long as there is nothing pulsating just go without it. Now we know the part of the story but there's more to it. There was a couple of other anomilies that need to be mentioned.  I've had the rig for a few years and always wondered if the steerable tag was in working order.  I never saw the tag wheels in my mirrors at low speed when turning so it was also on my radar to validate its operation. In addition after removing the FOD, Foreign Object Damage, the tag came alive and I could see them functioning in slow turns. That was a good moment for sure.  One other condition was my front wheel steering. Sitting still there were times when I could not turn the wheels effectively. When moving slowly and driving the steering control was normal. The most pressure required is highest when you are not moving. Well that also went away. Restrictions from the floating washer parts also migrated around and induced these problems as well. 

Worse case senario, I really don't want to think about but could have been catostrophic in my opinion. So my hope is to convey to all of you that have early steerable tags to be aware of this washer and I RECOMMEND, REMOVE IT ASAP. 

5. Conclusion
Food for thought. There has been hydraulic fan motors that have failed and I wonder if this condition could be a canidate for some of those. Steering tag and steering wheel control problems as well for sure. Also call Newell if you think you need more information and advice.  This is a real potential killer so I strongly urge that this becomes, as the FAA folks know an Emergeny AD "Airworthiness Directive". For now let's call it a Newell Service Bulliten. Unintended consiquences like this has taken down many aircraft, much more comforting pulling off to the side of the road!

[[email protected]]

Well here we go. This is a critical potential hydraulic emergency notification for the early steerable tag crowd. 

I'll do my best to convey the problem and yes, it is of DOT importance.  

1. Symptoms
2. Troubleshooting
3. Cause
4. Cure
5. Conclusion

1. SYMPTOMS

 Started out on a summertime trip looking forward to a relaxing get away.  As most of us know the relaxing part may or may not happen based on the rigs behavier. Three miles from home I start merging on the highway. 1 mile later I scan my instruments and I see I'm overheating. Pull over on the shoulder, leave the rig running and head to the rear.  The cooling fan not running.  First thing, I pull the connector on the manifold, still no fan. 

 I did install the fan overide cockpit controlled switch, or if adopted, in the official Newell Gurus Glossery, the FOCS.  Installing FOCS, IMO, is one of the best modifications to have in order to have some control for engine temp. Heat kills and so does my X wife when she feels the need.

Where were we? ADHD MOMENT.

 She's running around 215 degrees so I milk it to the next exit 1 mile away.  So since the fan is not working properly it's time to put my aviation skills to work. Check the hydraulic and coolant fluid levels, they are normal. Next I get my ball peen hammer and gently tap the manifold lightly repeatedly. Low and behold as I tap and the fan comes alive slowly. The more I tap the faster the fan responds. Within 20 secounds the monster is alive and spinning like she should. All is well so let's roll again and see how the temp is.  The temp stayed around 184ish so I feel comforitable and safe operationally. So I drove it this way for the excursion. 

2. TROUBLESHOOTING

Obviosly it first appears we have a spool valve that is not porting fluid properly within the manifold.  First step is to pull it out for examination. Suprisingly the fluid loss was minor when I pulled it out. Maybe 10oz but not much more. I examined the spool valve and orings and don't see anything that makes my eyes bug out. Next I put my finger inside the valve like a prostrate exam. There is someting in there so I keep examing the patient. The first piece I get out is a piece of metal and the 2nd 3rd and 4th piece are too.  This has to be the culprit but what the heck is it? The next move I reassemble what appears to be a big washer with an orifice drilled hole. They all fit together nicely, see pics.

It appeared that this was made intentioinally but for what purpose and where does it belong?  Time to call Newell on the bat phone.  I should have written down the names of the factory guys because without their knowledge this condition would forever keep me up at night. 

3. Cause
The pics of this washer orifice was uploaded and they said they would get back to me.  Maybe 15 minutes later I'm back live with the boys.  The guy they get gives me the Paul Harvey story. So Paul says, he remembers the issue, he goes back in time when they first encountered a pulsation after they installed the ZF tag.  He said when they first started with the steerable ZF tag there was a steering wheel pulsation that developed. 

4. Cure
Someone thought trying to reduce it by limiting the fluid flow and effectively dampening it. There was born the washer with a hole in it for the fix. Well it worked but in my opinion the fix was not properly done. I have worked on many hydraulic systems that use restriction orifices that either were bored out to a design specification in the manifold itself. Another method is to utilize a orifice fitting threaded into the manifold itself. Either way is considered a properly approved design or device. The washer was OK if it was used for developing a fix, but only temporary prototype testing.  Someone at Newell felt otherwise and used the homemade washer orifice as the cheap fix.

Anyhow, he asked if I had any pulsation issues with the steering wheel and I said I did not have any. He said, as long as there is nothing pulsating just go without it. Now we know the part of the story but there's more to it. There was a couple of other anomilies that need to be mentioned.  I've had the rig for a few years and always wondered if the steerable tag was in working order.  I never saw the tag wheels in my mirrors at low speed when turning so it was also on my radar to validate its operation. In addition after removing the FOD, Foreign Object Damage, the tag came alive and I could see them functioning in slow turns. That was a good moment for sure.  One other condition was my front wheel steering. Sitting still there were times when I could not turn the wheels effectively. When moving slowly and driving the steering control was normal. The most pressure required is highest when you are not moving. Well that also went away. Restrictions from the floating washer parts also migrated around and induced these problems as well. 

Worse case senario, I really don't want to think about but could have been catostrophic in my opinion. So my hope is to convey to all of you that have early steerable tags to be aware of this washer and I RECOMMEND, REMOVE IT ASAP. 

5. Conclusion
Food for thought. There has been hydraulic fan motors that have failed and I wonder if this condition could be a canidate for some of those. Steering tag and steering wheel control problems as well for sure. Also call Newell if you think you need more information and advice.  This is a real potential killer so I strongly urge that this becomes, as the FAA folks know an Emergeny AD "Airworthiness Directive". For now let's call it a Newell Service Bulliten. Unintended consiquences like this has taken down many aircraft, much more comforting pulling off to the side of the road!

Appreciate you adding this to the forum. 

Can you tell us where that washer was found? Was it behind where the coil mounts or the port above that?

[Richard]

Nice write up, thank you. This will help many in the future.

[orbit1957]

I forgot to mention the solonoid was removed as well as the spool valve in the same cavity. That's the location I found the failed washer. Thanks Jeff for pointing that out.

[Jack Houpe]

Great write up and entertaining!

[[email protected]]

I forgot to mention the solonoid was removed as well as the spool valve in the same cavity. That's the location I found the failed washer.  Thanks Jeff for pointing that out.

10-4, thanks for that. Hopefully this will help others.

[jdkskyking]

Orbit1957…. We need to talk… 
JK

[jdkskyking]

It’s been a few years since I marched down the gold hydraulic block path but I’ll try to recall what I know. I have a spare block… part of the di$covery phase of my journey… 

My coach is a little different with a Cat-13 engine and VICKERS 20 hydraulic pump but I’m betting the manifold is the same. I’ll speak to mine

You’ve been introduced to the spool valve and the orifice used to determine fan RPM in either low or high speed. It’s been a while since I tried to chase down manifold info. 

The manifold was designed by HydraQuip in Tulsa OK. The designer has moved on. 

In addition to the spool valve system there are two pressure relief valves, RV5 and RV6. The RV5 valve is the overall system pressure regulator while the RV6 valve protects the ZF Steering Gear box.
The ZF Gearbox also has its own internal pressure relief system, the RV6 is an extra measure of protection. 
On mine… if I recall, RV5 should be set somewhere around 2250 psi and the RV6 is set at a lower pressure, 1800 psi ish. On the forward side of the block you should find the values stamped in the block. Your pressures may be different, I’m assuming a DD60 and a different hydraulic pump.

On mine, LOW SPEED FAN is equivalent to 1/2 the engine RPM. If the Engine ECM calls for HIGH SPEED FAN the ratio is 1 to 1.

If I recall, my orifice disc was stainless steel. 

Eliminating the orifice disc could change behavior of the fan RPM system. 

I do know that the system was designed to share hydraulics and in LOW priority goes to the ZF Steering Gearbox. In HIGH…. The fan is the priority and the gearbox gets what is left over. 

BTW
The ZF RAS System hydraulics is a separate closed loop system that incorporates a hydraulic pressure accumulator to function properly. 

The forward “MASTER CYLINDER” utilizes gearbox hydraulic pressure for assistance moving the internal components of the cylinder but is not directly involved in moving the TAG tires. I’ve posted extensive information about the ZF RAS system. 

The ZF RAS Pressure Accumulator has a 10 year life span. If you have an original it should be replaced or the TAG steering system will not funny properly and can become inoperative to the point you will not be able to back up your coach in certain circumstances. The TAGS will caster forward but not backwards like the front wheels of a shopping cart. 

I’m here to help if you need anything. 
JK

[Richard]

I am dogpiling on this post, just in case an owner with steering problems stumbles upon this thread using a search engine.

Let add a couple of key points that are covered in other posts on similar topics.

One, if you have the gold anodized aluminum block that controls the hydraulic pressure to the fan and steering gear box, you must understand that the priority is to the fan when the high fan circuit is activated by the engine computer. That prioritization can have unintended impact on the steering gear box IF there is a problem with the hydraulic fan motor.

So what you say? IF the internal seals are blown in the fan motor, it will negatively impact the steering. There is no outward or visible sign that the seals are blown. Here is how it will manifest. The coach will have steering until the engine reaches operating temperature, and then the steering will suddenly degrade when the engine computer activates the fan. When the internal seals are blown, the hydraulic pressure flows around the gears in the pump without restriction, and flows out the return line. None goes to the steering gear box when this happens. One owner replaced steering gear box and hydraulic pump before finding the root cause.

There is a derivative of this fail mode. The fan motor can fail at the front seal. In that case, you will know you have a leak because of the mess in the engine bay. It is hard to tell if the leak is the fan motor or the overhung load adaptor. Again the symptom is noticeable loss in power steering.

For those of you with steerable tags, either of the above situations will make the coach EXTREMELY hard to drive. Part of the steerable tag system has an independent hydraulic system to recenter the tag wheels. It takes the power of power steering to overcome the self centering feature. The coach will be almost impossible to turn the wheel at slow speeds.

Again, all the above info is contained in other threads that posted over the past ten years. My summarization was an effort to help someone in the future, and not to steal other’s post or pose as the subject expert.

[jdkskyking]

I agree Richard. 

Regarding the self centering of the ZF RAS system.

ZF has specific values for the pressure accumulator nitrogen charge and for the “hydraulic” side of the closed loop system. ZF provides the pressures in “bar”.

I personally believe the ZF recommendation for the pressures are to provide proper operation AND allow the driver to “overcome” the ZF RAS centering system in the event of a hydraulic system malfunction. 

If memory serves:
ZF RAS Pressure Accumulator:
Nitrogen charge 10 bar (145 psi)
Hydraulic charge 15 bar (218 psi) 

I know for a fact that the RAS system functions perfectly at these values and I was able to overcome the centering system with the engine in off, steers and tags on pads to allow the system to function. 

The key to success with the ZF RAS system is bleeding the air before setting the pressures. 

Don’t forget, pressure accumulator “pressure” should be checked annually and the bottle replaced after being in service 10 years. 

JK