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Old 10-12-2017, 06:11 PM   #1
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Rear Air Tank Pressure Alarm

2006, 43' Mountain Master with IFS...

Pulled into Garden of the Gods Resort in Colorado Springs and as we started backing into our spot the rear air tank alarm came on. I didn't see any immediate affect at that time.

After we got it backed in I dumped the airbags and then tried to air them up. On high idle I got the air pressure on the rear tank up to about 70 PSI and the alarm went out. The rear air bags appeared to air up as normal but the front bags took a very long time. Also, I never heard the air compressor governor "pop".

This might be important or not but...both the front bags appear to inflate at the same slow rate. That would seem to point to a common connection but that is truly a wild guess.

I've made contact with Auto-Truck Services but they are booked out until the 26th. I've contacted Trans West in Fountain and waiting for a call back from their mobile tech.

Obviously, my first concern is whether or not the coach is drivable for a relatively short distance to get to a shop. If I can get the coach to hold 70 PSI or better is that good enough. However, will braking deplete the rear tank and if so...that ain't good.

So, based on the situation where the rear bags come up normally I'm assuming that my problem is "up front". Also, given how slow the front air bags are inflating I'm not thinking it is a bad sensor. Also, since the governor isn't won't "pop" I'm thinking it is an air leak but in the frustration I didn't take the time to listen for a leak. Perhaps tomorrow when I get my brain thinking more clearly (with your help. LOL) I can bring the slides back in and air the bags up again to listen for a leak.

Any thoughts or suggestions are welcome.
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Old 10-12-2017, 06:28 PM   #2
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The compressor isn't going to unload ( pop ), until there is 120 psi in the tanks.

If it seems to pump up to 70 psi at the normal rate and then slow down, I would definitely look at the supply lines to the front air suspension.

The system is designed to block the air supply to things like air suspension, air horns and other acessories, if the pressure drops below 70 psi. That preserves the air supply for braking.

As far as driving, if the pressure remains above 70 psi, you should have good enough braking for driving it to a nearby shop.

If the pressure drops below 45 to 50 psi, the parking brake is going to come on automatically and leave you stuck where ever that happens, until you can build back up above 70 psi.
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Old 10-12-2017, 10:29 PM   #3
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OK...maybe I need some serious education. I'm going to break this down to basics. This may come across as some "OH DUH!" questions but I need to confirm things.

I found the attached diagram from a 2003 Travel Supreme. While there could be some minor differences I would assume that the basic layout is good enough for comparison.

That attached diagram doesn't use the term Front or Rear tank. The pressure sensors are labeled 1 & 2 so...

It would seem to make sense that my "Front Air" gauge would (should?) monitor the tank providing pressure to the front brakes, suspension air bags and accessories. That would have to mean the "Rear Air" gauge monitors the tank providing air pressure to the rear brakes and that it also provides controlled pressure to the front tank. Is this correct?

Of course, there is the possibility that the gauges are "backwards" from my logic.

So...anyone know if front = front and rear = rear?
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Old 10-13-2017, 12:28 AM   #4
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Both tank #1 and tank #2 are supplied by a third, wet tank.

Your diagram may show only 2 tanks, but one is a 2 chamber tank. The wet tank is the first tank in the system and supplied by the compressor. It has no gauge, but is the tank that controls the compressor governer. From it, air is delivered to both primary and secondary tanks thru a double check valve tee.
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Old 10-13-2017, 02:05 AM   #5
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You have a two tank system, one for brakes, one for all your other air acc.'s!
The wet tank supplies both, and is where your air first goes from your compressor!
All air brakes on MH's to Semi's have the same system!
The air goes from the compressor to the wet tank, out of the wet tank to the main tank for the brakes, and then to the other tank, (aux) for your acc.'s! Some may be plumed to both at the same time?

Did you let it run long enough to fill the system all the way up, or is it just filling to 70 PSI and that is as high as it will go? Do you have separate gauges,(air) or the single gauge with two needles, (red and white/black) Red needle is the main tank, and is for the brakes, and the white/black needle is for the aux tank!
If it is only building to 70 PSI, and not any more, then driving it would be very risky, as you must have a major leak! I would call a Mobile Tech to check it out, if you have already looked at it and can not find the leak!
How fast does it leak off from 70 PSI after you shut the motor off with the brakes set? Have you tried to release the brakes after obtaining pressure? What does the gauge do then? Did you step on the peddle after the motor is shut off, and look at the gauge, to see if it drops or holds steady?
Many things could be wrong, split wet tank, split line from wet tank to main tank, broke brake line, on and on? Until you find the leak, I would not drive it as if the pressure drops much below 70 PSI, the brakes will start to apply, and you will be stuck!
Good luck, it is probably a easy fix, if you can locate the problem!
Rail!
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Old 10-13-2017, 02:19 AM   #6
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Here is a simple diagram that will help you visualize your braking system!
https://www.bing.com/images/search?v...=21&ajaxhist=0
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Old 10-13-2017, 06:07 AM   #7
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Quote:
Originally Posted by guardrail53 View Post
You have a two tank system, one for brakes, one for all your other air acc.'s!
The wet tank supplies both, and is where your air first goes from your compressor!
All air brakes on MH's to Semi's have the same system!
The air goes from the compressor to the wet tank, out of the wet tank to the main tank for the brakes, and then to the other tank, (aux) for your acc.'s! Some may be plumed to both at the same time?
:
This is not how dual air brake systems work.

The front brakes operate from the secondary tank and the rear operate from the primary tank. Accessories can be tapped into either system as long as there are protection valves at the tank.

It is designed this way, along with check valves, so a total failure of one system will not leave you without brakes.

Your diagram even shows this.
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Old 10-13-2017, 07:31 AM   #8
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Hey SkyBoss,

I believe you are looking at the diagram I put together. With that said, here are a few questions that will (I hope) help you figure out where your problem is.
1. When was the last time you change your Air Dryer desiccant filter?
(It's located on the passenger side frame rail behind the rear wheels in most cases)
2. Are Both Gauges reading the (roughly) the same pressure?
3. Is the rear suspension coming up?
4. If so, How long does it take for the rear to come up?
5. Is the front suspension coming up?
6. If so, How long does it take for the front to come up?

Since you are out on the road, I'm not sure what tools you have available, so unless you can do this safely, don't get under the coach.
The Front ride height adjustment valves are behind the front wheels, toward the top of the wheel.

7. You should have 3 Moisture ejectors. A lot of coaches have lanyards that can be pulled to manually activate them. If your coach does have lanyards, then pull them one at a time and watch for water under the coach behind the front wheels toward the center of the coach. Any water???
8. Get some soapy water and spray each of the front ride height adjustment valves. Do you see any bubbles? Left or Right side?
(The front valves are the usual culprit since they take the most wear and tear when driving.)
9. After checking the front valves, the rear valve is next. BUT ONLY IF YOU CAN GET Under the coach SAFELY. (That means blocking the coach up so it doesn't crush you if the suspension drops.) The rear valve is located on the drivers side, just about over the rear axle, maybe slightly forward of it. Any bubbles?

Answer as many questions as you can SAFELY. Let us know and hopefully we can help you further.

Drew
2003 Travel Supreme 40DS02
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Old 10-13-2017, 08:03 AM   #9
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I'm pretty confident that my first diagram is basically what I'm looking at. BTW...this is not an official Spartan diagram but looks like a very knowledgeable person put this together in a very logical way. I can see that there are some specific part numbers and location identifiers that could be specific to Travel Supreme but I think the basics of the pressure system are probably accurate for my needs.

I'm also thinking that my problem won't require searching for the holy grail but I am taking this as an opportunity to upgrade my knowledge. As an operator I know how to apply brakes and do a brake check. However, I'm not a mechanic so that is why I might be asking too many questions. LOL

So..

To start with I do understand that the accessories can be driven from either tank and that different manufacturers will have different schemes. As an example, I have seen a Monarch schematic that runs air bags off of both tanks. Keep in mind they have 8 or 12 air bags.

Working with the Spartan diagram I have I am assuming there aren't any huge differences to how Spartan approached its design from 2003 to 2006 even with 2 different brands. Starting with the basics...

1. The compressor provides pressure to tank 1 (combo wet/dry). I won't even pretend I know how that tank works between the wet and dry side but for now I don't think it is important.
2. In the loop of connections to and from tank 1 are air dryers, governors and systems to maintain a regulated pressure in tank 1.
3. Tank 1 provides pressure to the rear brakes.
4. Tank 1 also provides pressure to tank 2 through a pressure check valve. I assume that is to isolate tank 2 from tank 1 in case of a failure in tank 2 and/or visa versa.
5. Tank 2 provides pressure to accessories, air bags and the front brakes.
6. In that loop of connections to and from tank 2 are different control and pressure lines that get involved. They provide air pressure to front and rear air bag systems along with systems that control pressure.
7. There is a master inflation/deflation valve in that diagram that is connected to tank 2 and also to individual inflation/deflation valves to each air bag system. This (or at least its exact configuration) could be more specific to TS coaches since there is some kind of equalizer dash control. However, I imagine it is still part of the DSDP system in some form. I'll leave that in the "FM" category of "freakin' magic" for now. However if I were to hazard a guess it would be that the master valve is tied into my HWH system for dumping air pressure whether that is all bags when putting jacks down and removing some pressure on the tag when in reverse or activating the tag pressure button.

Am I missing something at this point on general system layout?

So this goes back to a primary question. Is "tank 1" the front or rear pressure gauge on my dash? Of course, answering that tells me which tank is monitored by the other gauge.

OK...I'm going to hazard a guess to my own question. I'm thinking my rear air pressure gauge that is giving me a warning is connected to tank 2. My reason is that if tank 1 was having a loss of pressure that it wouldn't be able to fill tank 2 so I would get a low pressure on both tanks in that case. Hey...it is a wild guess but goes counter intuitive if one is trying to relate the gages to the affected brakes.

One other question is the pressure protection valve located between tank 2 and the connector block for the air bag system. Would this valve protect the air bag system from deflation in the event of loss of air pressure to tank 2?

Time to call Spartan!
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Old 10-13-2017, 08:26 AM   #10
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You need to think of your system having 3 separate tanks.

One tank is filled, thru the air dryer, from the compressor.

That wet tank fills the other 2 other tanks.

The larger single tank has a wall welded in it, separating it into a large and small section. The weld seam is visible on the outside of the tank.

There is no magic connection, the outlet of the smaller section tee's to the larger section with a line and the other tank with a line.

If the leak in one of the 2 tanks isn't big enough, the other tank can fill higher.
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Old 10-13-2017, 09:36 AM   #11
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Sky Boss,

I just went through the same problem recently. My Problem began after sitting parked in a CG for a couple of weeks. Had trouble getting it to air up when we were ready to depart. After playing and cursing for a while it cut in, aired up to 120 PSI and off we went. Over the winter, I replaced the air dryer assembly and the governor so I wouldn't be stuck on the road again. Everything worked as it should.

Then the following summer after a couple thousand miles,
Come off the highway into a small city and stopped at the first traffic light. The air dropped to about 90 PSI and the front suspension dropped. If I pumped the brake to exhaust the air below 70 PSI it would start to build air again up to cut off at 120. But driving a few blocks and again, same problem. Had to stop, pump the brakes, build up air so I could move.

I got to a Wallyworld lot and got a mobile mechanic to come out. After trying to adjust the air governor with limited success, he had another used one in his stash which he installed. That seemed to do the trick and got us home for about 500 miles and through the mountains.

After sitting in the garage all winter, first trip out, it did the same thing again. This time I had it towed to a Spartan Authorized truck shop.
They played with it for a couple days and came to the conclusion I needed a new air compressor to the tune of a few grand. They were convinced the valves in the head were not seating and causing the loss of air. I tended to agree but when it worked, it worked well. Why sporadic?
Again, after more head banging, they came across a Cummins Service Bulletin for this problem. The fix was to install a small container (3-4 oz if I recall correctly) of ATF in the governor line and run the engine. When the governor sent the signal to unload the compressor, the ATF was injected into the head to essentially decarbon the valves.
Well, they gave it a couple of these treatments and the system now works better than it ever has. Builds air from below 70 to 125 in half the time it used to.
Cummins actually has a part number for this little gizmo.
I thought I had a PDF copy of that bulletin but can't track it down at the moment. I'm sure a Cummins shop will be able it find it or if you're on Quickserve you might find it yourself.
I get the impression this problem is more prevalent on RV's than trucks because these things sit for long periods and the carbon under the valves tends to accumulate rather than being expelled with steady operation. The guys at this truck shop had never run across this before.

Hope this helps,
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Old 10-13-2017, 10:07 AM   #12
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I just got off the phone with Spartan. Here is the official technical drawings for the suspension of my coach. I certainly learned something from it. All along I was totally ignorant to the fact my tag has bags. I know, you would think I knew better but the way it was explained to me must have confused me on that. So...I'm smarter now.

The diagram doesn't have how/where the brake system is tied into the air pressure system and tanks. It does have a reference to an air gauge but doesn't identify it. I'm pretty certain it is the rear gauge now. It all makes sense because when I dump air bags the rear gauge drops. That doesn't answer the question on whether or not my front and rear brakes are connected to separate tanks but I can live without that knowledge for now.

This is a very bare bones drawing and I am missing some page(s) with more information on the meaning of some symbols on it.

I've got a mobile tech that will come out Monday morning. He is known to be competent on air suspension issues. Between now and then I will come of the jacks and try to air the system up to see if I can spray some soapy water on the places that are obvious to me. I just wondering if the perception that the front bags not airing up isn't throwing me a red herring making me concentrate too much up front.

For me, the trick will be physically locating all the potential points where things connect together. I'm assuming that the leak is not in a line but is at these points.

Time to get dirty. LOL
Attached Files
File Type: pdf AIR BAG PRESSURE SYSTEM DIAGRAM.pdf (379.0 KB, 30 views)
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Old 10-13-2017, 10:15 AM   #13
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Quote:
Originally Posted by dennis45 View Post
...
Then the following summer after a couple thousand miles,
Come off the highway into a small city and stopped at the first traffic light. The air dropped to about 90 PSI and the front suspension dropped. If I pumped the brake to exhaust the air below 70 PSI it would start to build air again up to cut off at 120. But driving a few blocks and again, same problem. Had to stop, pump the brakes, build up air so I could move.

...


Again, after more head banging, they came across a Cummins Service Bulletin for this problem. The fix was to install a small container (3-4 oz if I recall correctly) of ATF in the governor line and run the engine. When the governor sent the signal to unload the compressor, the ATF was injected into the head to essentially decarbon the valves.
Well, they gave it a couple of these treatments and the system now works better than it ever has. Builds air from below 70 to 125 in half the time it used to.

...
So, when you had this happen do you recall if you had good pressure on the front and bad on the rear? When you pumped the brakes was that to bring the front tank down?

I will see if I can find that SB and post it here. Certainly something to keep in mind!

THANKS!
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Old 10-13-2017, 10:45 AM   #14
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Originally Posted by Sky_Boss View Post
So, when you had this happen do you recall if you had good pressure on the front and bad on the rear? When you pumped the brakes was that to bring the front tank down?

I will see if I can find that SB and post it here. Certainly something to keep in mind!

THANKS!
First encounter at the CG I could not build air at all. After sitting on high idle, pumping the brakes to totally exhaust the air, it finally began to build to 120. At that point I figured it was a governor problem and since it had been a couple of years since I had replaced the air dryer canister I decided to renew both.

But then when it failed the following summer, the air pressure in the system on both gauges dropped to 90 PSI just as I was coming up to a traffic light.
Again by pumping the brake to deplete all air pressure, it would cut back in and build pressure.
What was really happening was the unloaded in the cylinder head of the compressor would stick in the unload position and when the brakes were applied during a normal stop, the air pressure would drop below the set point of the governor but the unloaded would not cut back in until I reduced the air pressure such that there was no longer pressure under the unloaded and it would reset.

At about 90 PSI is where the suspension drops. There is still sufficient air to brake at that point but the air bags are deflated. Repeated pumping of the brake pedal would bring the pressure down to zero eventually and the air compressor would load a begin to build air to 120.

In your case, you might try, with the engine running, pumping the brakes to reduce air pressure to below 40-50 PSI (this is where the park brake should set) and see what it does. If it starts to build up to set point and raises the coach front and rear, chances are you have a sticky unloader as well. The fix is simple.
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