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OLD Prevost level low system
Hi Folks,
I am new to the forum but not new to owning an older Prevost Liberty Coach motor home. First of all if I offend anyone or fail to follow correct protocol, I appologize in advance, it is due to ignorance not arrogance.
I have seen/read several very good posts about air suspension/level low systems on Prevost motorhomes. Mine is a 1985 XL model and it is quite different from the ones pictured/described in this forum. Naturally, I did not buy this coach new so I cannot venture a guess what may have been changed by other than factory Prevost or Liberty Coach technicians. The system I will be talking about has worked fine for about 4 years that I have owned this coach.
First I do not have rocker switches at the left hand of the driver. I have (3) three position push switches labeled as left rear up/down, right rear up/down, and front up/down. There is a fourth push switch with only two positions and it is labelled “Level Low” When this fourth switch is engaged a red light next to it flashes. Now I assume these perform the same function as the newer rocker switches. They all seem to be functioning.
Below deck in the steering and auxillary air tank compartment is where the differences become severe. I do not have a bank of coils and valves with red caps on top of them as described in all the articles in this forum. I have the auxillary air tank, several (about seven) square block type relay switches and last but not least a panel that has mounted on it (6) six cylindrical shaped objects that I believe are solenoid valves. They are configured as two verticle columns of three valves in each column. These solenoid valves are plumbed with 1/4 inch or smaller pipes that deliver air pressure to the right hand column, which are connected to the left hand column then the left three valves have exhaust mufflers on each one.
Now for my problem. The front air springs do not inflate. They do not operate in either drive mode or level low mode. The rear inflate to ride height just as they should. My three air pressure guages on the dash show normal air pressure. the two top guages show 100/110 lbs and the third lower guage which I assume is for the auxilliary air tank runs up to 120 lbs.
Now for my questions. Has anyone else had experience with anything close to what I have described? Any info about anything similar would be appreciated. Next, any suggestions about how to roubleshot my problem also would be appreciated.
Sorry for being long winded, I reall appreciate any help.
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16 Replies
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Welcome aboard. Don’t worry too much about protocol or procedures because we have none.
You pose good questions, but I think for anyone to offer advice it would help if you added some information, perhaps in your signature line. Specifically for this post I would want to know if your coach was a professional conversion such as by Liberty or Marathon, and if not was it a seated coach originally. The fact you mention Liberty leads me to assume it is a Liberty conversion.
Based on that assumption I can make a general comment. When you select the “road” or “driving” position on your switches the suspension system height is determined by ride height valves which are supplied air by virtue of a valve at each of three positions that opens a path to each of the three ride height valves.
When you switch to a manual control of the coach suspension system the same valve at each of three positions shifts and you control whether you add or dump air to the suspension at each of the three positions by pressing a switch that controls valves that introduce air or cause air to exhaust from the air bags.
Now to surmise what is happening based on your description…….if the front will not go up or down regardless of the position of your switches but the left rear and right rear will I strongly suspect your problem is in the valve that shifts to put air through the ride height valve or to put air into the air bags in the level low position. In later model coaches, and possibly yours that valve would be a five port Norgren valve and it would be located on the rear bulkhead in the steer compartment under the front electric compartment.
Usually when a spool valve fails to work it is the coil or solenoid valve that sends a pilot air signal to shift. I rule that out because the rear valves are working. In this case I suspect the valve is not shifting possibly because of moisture or internal corrosion. See if you have that five port valve and pull it out. With great care you can remove the screws that hold the end caps in place and if it has failed the reason why will be apparent.
If you do not have Norgren valves check with Liberty or Prevost to see about the availability of a replacement valve. I do not know for sure, but suspect the basic operating principle of your suspension control system is very similar if not the same as coaches built today.
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There is a busnut down around FT Walton Beach that has about same yr as yours and system. I will see if I can get contact info for you. Bob
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Dagored1
Sounds like your system works off of electrically controlled solenoids so I would start by determining which column of solenoids controlls the front. Have someone work the switches while you feel or listen for the solenoids clicking. If one is not making any noise then that is most likely your front system. Check if you are getting power to the solenoid, if not find out why? Jump voltage to it and see if it functions. If the electrically part is OK then check if the system is getting air and allowing air to past thru it to the bags.
Have you tried to find the schematics on PrevostCar site? There is a link on this site to them.
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Checking the operation of the solenoid valves is not a bad thing especially to determine which one actuates when you select the driving position. When a coach will not go to the driving height it is almost always the coil on the drive height solenoid valve that has failed, usually because that solenoid is always energized when driving.
But if you have selected the driving position and just the rear of the coach goes to the correct height for driving then the problem is unlikely to be the solenoid coil or valve. In that case verify the valve is functioning just by loosing the air fitting from it and listening or feeling for air escaping, and then go to the actuator on the end of the five port valve to verify it is getting air (there should be two?) and if it is then start looking seriously at that valve as the problem, unless the ride height valve has failed or has become disconnected. The fact you cannot raise the front manually or in the drive position almost rules out the ride height valve as part of the problem.
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First, thanks to all for quick replies. I have more info. My bus is a pro conversion done by Liberty. It was never a seated coach. A little more about my problem, or rather my bus’s problem, mine are beyond help haha.
Inside the access door for the steering, auxilliary air tank and level low system just below the electrical compartment door and underneath the drivers seat I can hear a rather pronounced air leak. Further when the engine is shut down, I can watch the auxillary ari pressure guage on the dash drop from 120 lbs to zero in a matter of very few minutes. I have not been able to pinpoint the leak because it seems to be too far inboard, towards the centerline of the coach. I am thinking I will drop the bumper and see if I can do any better from inside the spare tire compartment. I am a little skeptical about that because the spare tire compartment is full of two cruisair a/c units. I thought of going after it from inside the forward cargo bay but that has been lined with plywood and outdoor carpeting.
One more question. It seems a little embarassing but here goes. Ignoring aftermarket changes or “improvements”, what is the recommended procedure for accessing the front levelling valve. I see it on drawings as somewhere in the center of the chassis. I know it controls the height of the body from the front axle and all but I just cannot see it. The rear ones are easy as they are mounted outboard and are fairly obvious. I assume I am looking for the same typr of hardware as the rear valves just located on the front axle near the center. Maybe this seems simple minded but I just cant find it.
Thanks for your help
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I always forget something. I’ll be short. There is a repair shop nearby with 60,000 lbs lift. Can a professional tow my coach in its present condition without the front airbags inflating? Thanks, Mike
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Mike,
A professional should be able to tow your bus as long as the nose can get high enough to allow the wheel or axle lift to get beneath the front axle or tires. If the nose of the coach is down too low you might be able to work it higher by rolling the front tires on some boards or a stack of boards. A number of owners have created drive on ramps to elevate their coach so they can service them so that is not an unlikely solution to getting access for a tow truck.
Having said that if you are inclined to do your own work you can actually make a set of ramps from 2 X 10 or similar, stacked together sideways and bolted together. But whatever you do never ever get under the coach unless the chassis is supported or the coach is all the way down. NEVER EVER trust the air bags or suspension system to remain up, especially when you are working on the suspension. The chassis should always be supported prior to going under the coach and where to support it can be found on the Prevost site for your vintage coach.
You can look under the coach a little by turning the steering wheel all the way left or right and then looking through towards the center. That may help you at least see the area the leak is coming from. Is it possible the leak is an air bag? That would certainly explain why the front will not rise. And if it is it is a sure bet no matter how big the leak is today, it is going to keep getting larger. If that is your problem turning the tires will make a portion of the air bags more visible enabling you to verify that.
Air bags are easy to replace if you have the patience and some basic tools.
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Member name with about same system. ( Depewtee ) Bags never inflate? If you can get it up on boards and safetly blocked. or wheel turned so you can check out air leak it will probably help or fix your problem. Could be as simple as a disconnected rod to the front leveling valve. As a word of caution never get under a bus without blocking it up! It only has to fall once! Don’t trust a jack.. Bob
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Put your hand at the bottom of the brake valve once and see if you can feel the air coming out. If so,replace it with a new part from Prevost, not a rebuild. The engine compressor probably cannot overcome the rate of loss enough to raise the front.
That valve is in the steering compartment, I think its called a shuttle valve.
Also in the same neighborhood, if you have an air floor over the stairs, might be the air solenoid for that leaking.
Don’t ask how I know this stuff.
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Dagored1,
As Bob mentioned I have a similar vintage coach as yours. Mine is a 1981 Prevost Motorhome chasis with a Liberty conversion. The level low system you describe sounds identical to mine. I am in St. Pete for the week, so I do not have access to my coach. Upon my return home I will be happy to take any pictures you need or provide any feedback on how my systems work. I had similar problems with my passenger floor slide actuator leaking as well as a leak in the line that supplied air to the air bags for the generator. It is amazing how many places there are for air to escape!
Brian
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Hi folks, here is an update. I found the obvious leak. It was a blue 3/8 inch nylon line that had failed(cracked) where the line enteres a manifold/valve dead center on the forward bulkhead in the spare tire compartment. Clipping off the cracked portion of the line and replacing the fitting fixed the air leak. But alas, that did not fix the front air bag problem. I still had no or insufficient pressure to raise either front air bag.
Further investigation with bus up on leveling blocks showed a solenoid valve adjacent to the front height leveling valve with a blue 3/8 inch nylon tube entering the solenoid valve, then exiting the valve and routed into a TEE fitting that feeds both front air bags. Removing the blue line from the inlet fitting to the solenid valve showed we had air pressure up to the valve but none coming out and getting routed through the TEE fitting to the front air bags. Simply by bypassing the solenoid valve and routing the incoming blu line straight to the TEE fitting we got the bus to raise to proper ride height. Now we can drive the coach but the level low is not functional. The ir line is still being routed through the ride height leveling valve but not through this solenoid valve in the same location as the leveling valve.
The PDF drawing I downloaded from prevost is half French, half English and all lousy quality drawing and writing. I do not know what the solenoid valve is called, its part number or its function. But that is progress.
Thats all for now and as usual any further info/insight will be appreciated.
Thank You, Mike Felice
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Hi Mike,
I too have an older model Liberty conversion and I am presently having the same issue with my front ride height coming up. I can manually push the front button to introduce air to my airbags and raise the coach up to drive it, but it will not do anything on its own. I saw that you mentioned a bank of valves in the side access next to the tank, can I get you to snap a picture of it and post it here? I cannot find anything that resembles the solonoids or norgrin valves that have been mentioned in several posts and helps here. I have met and gotten some really great replies from many folks here though, they have been a great wealth of knowledge, so keep posting….
Richard
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Richard,
I will be glad to take some pics but right now my bus is in the shop. As I mentioned in my last post we found the obvious leak, cracked blue nylon 3/8 inch line entering a manifold/valve located dead center on the forwad bulkhead accessed from the spare tire compartment. That did not solve my problem though. We followed the blue air line as it went through the bulkhead and to a solenoid valve located directly above the front axle also directly in the center of the bus. it is the same location as the front lever-action leveling valve. In my case we simply bypassed the solenoid valve re-routing the blue air line around the solenoid valve and directly into TEE fitting that leads to both front air bags. At that point the bus raised up as normal for driving position on its own. The level-low switches inside the bus are still not working but it is ok for driving. Now the bus is in the shop where they are attempting to locate a new solenoid valve to replace the one we bypassed and return the line to its proper position. Obviously this solenoid valve has something to do with allowing the air to pass into the TEE fitting and then the air bags. I assume it is controlled by the switches inside the bus to put it in driving position or level-low position. Hope this helps.
OH yes, in my bus the bank of cylindrical switches/valves inside the front access door under the drivers seat are gold in color and are mounted just outboard of the steering gear box. They are one of the first things you see when you open the access door. They are plumbed with air lines and have electric wires running to them.
I will post pics when I get my bus back.
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One thing that I consider an important part of suspension diagnosis is to try as many different things as possible to see if a problem that shows up in one situation, doesn’t exist in another.
For example, if a coach will not return to the driving height when the knob or control is in that position, but the coach can be manually raised or lowered that narrows the choice of potential defective components. To use the example of a front end not coming up to the driving position, but can be raised using the controls manually that rules out issues with system pressure. There is enough aux pressure to do the job. That leaves a ride height valve, or a leveling valve or the solenoid controlling the leveling valve as the culprit. (On current or late model coaches that would be a 5 port Norgren) It could be the 5 port valve shifts properly for manual operation, but fails to shift to the driving position. Or it could mean the solenoid valve that controls the five port valve is bad.
The point is following the air is often the easiest way to isolate and rule in or out which components are OK and which are defective.
I might be wrong but the valve type used on coaches prior to the use of Norgren valves can be replaced with Norgren valves that perform the same function and that the system logic is basically identical to later production models. That means Hector’s article on the air suspension is a good starting point.
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