Front won't go up or down?

[HarborBus]

I just have the Prevost manual leveling system. The rear right and left level works fine but when the switch is turned to the front nothing happens either up or down. I do know there is only one valve in the middle of the chassis on the front. I just discovered it so I haven't checked anything yet. Where do I start?

[Jon Wehrenberg]

Elliot,

There are several possibilities such as the selector switch (my guess) or a defective solenoid valve.

The selector switch is a rotary switch not likely to fail, but it could have a loose connection. I would start there and check it for tight connections and continuity.

My second choice, but easiest to check is the second solenoid down on the solenoid manifold under the driver's seat. It is a stack of five, mounted on the rear bulkhead and is a row of black solenoids identifiable by the red caps. This can be checked by listening for the valve to "click" when you select the front position on the rotary knob and then alternately press the up and down. In the "UP" position you will hear that valve and the one above it click, and in the "DOWN" position the second one down should click.

These solenoids are opening the air circuit to the five port Norgren valve which should be located below or near the solenoid valve manifold. If they appear to be working loosen the small end air connections to verify the valve is getting air signals.

If neither click it is likely the rotary switch, if the second one down fails to click it is likely the valve. If they all work and the Norgren is getting air, it may be the culprit.

As near as I can determine the Norgren five port valve, rotary switch and the second solenoid down are the only common parts to making the front go up or down.

Hector created a wonderful tool which I used to make the analysis and it is available to POG members. It is the Prevost Suspension Demonstration power point and if you can access it through the POG site or get Hector to provide it to you it will help you sort out this problem. It is not going to be difficult or expensive for you to tackle, but an inexperienced mechanic that does not understand your system will burn through your money at an alarming rate.

[MangoMike]

Elliot,

Here is the red caps Jon was referring to.

Some more info over at Prevoman.com that may help you.

http://www.prevoman.com/Pages/Manifold/Manifoldpg1.html


5419

Mike

[HarborBus]

Thanks Jon and Mike I will check out the switch and see what I can do with the solenoids. Could you explain why there are 5 solenoids and the assignment of each. In my simplistic and uninformed brain it would seem there would only be 3 solenoids, one for the front, one for the right rear and one for the left rear. It probably has to do with the 5 point Norgren valve ie, one solenoid for each port. Which brings up another question, why does the Norgren valve only have 5 ports? Common sense would dictate that it would have six ports UP and Down for each position? I know I'm going to be a handful when it comes to teaching me how to work on this bus. I can fix almost anything, it's the diagnostics that I have trouble with.

[dreamchasers]

Harborbus,

Below is the link to the presentation that I made to understand the function of the Prevost leveling system. The pneumatic systems on the Prevost are complicated. I have not accessed the presentation in a while, so I hope that it is compatible with IE8. If you do have IE8 installed, try clicking the compatibility button on the tool bar if you have any issues.

http://forum.prevostownersgroup.com/showthread.php?t=2116&highlight=airbags

I hope this helps.

Hector

[tdelorme]

Elliott, I would start by parking the bus with the front slightly downhill and then hit the "auto" rocker switch and see what happens. If the bus doesn't try to level itself, then I would "exercise" the system by going from one rocker switch to another. Also, be sure the selector rocker is in the manual position if nothing happens in the auto position. If all that fails, then do the Jon stuff and see if you can locate the problem. Good luck, I bet it's something simple.

[HarborBus]

Thanks Hector and Ted, I now understand the use of the 5 solenoids (thanks to the drawing). Ted I don't have an automatic for leveling on the switch, all I have is the drive(off) position, Front, left and right for manual leveling. Additionally I have the two rocker switches for up and down. I will try your suggestion of exercising the up and down rocker switches while selector switch is in the front position. It would be nice if it is just a stuck solenoid.

[HarborBus]

Jon, what do you think about switching the wires(after labeling of course) on the selector switch. Example: put the left position wires in the front position of the switch and the front position wires in the left position to see if the switch is bad?

[rahangman]

Elliot,

There are several possibilities such as the selector switch (my guess) or a defective solenoid valve.

The selector switch is a rotary switch not likely to fail, but it could have a loose connection. I would start there and check it for tight connections and continuity.

My second choice, but easiest to check is the second solenoid down on the solenoid manifold under the driver's seat. It is a stack of five, mounted on the rear bulkhead and is a row of black solenoids identifiable by the red caps. This can be checked by listening for the valve to "click" when you select the front position on the rotary knob and then alternately press the up and down. In the "UP" position you will hear that valve and the one above it click, and in the "DOWN" position the second one down should click.

These solenoids are opening the air circuit to the five port Norgren valve which should be located below or near the solenoid valve manifold. If they appear to be working loosen the small end air connections to verify the valve is getting air signals.

If neither click it is likely the rotary switch, if the second one down fails to click it is likely the valve. If they all work and the Norgren is getting air, it may be the culprit.

As near as I can determine the Norgren five port valve, rotary switch and the second solenoid down are the only common parts to making the front go up or down.

Hector created a wonderful tool which I used to make the analysis and it is available to POG members. It is the Prevost Suspension Demonstration power point and if you can access it through the POG site or get Hector to provide it to you it will help you sort out this problem. It is not going to be difficult or expensive for you to tackle, but an inexperienced mechanic that does not understand your system will burn through your money at an alarming rate.
Jon, so why do I have a stack of only 4 solenoids on my 1990 CC???


My second choice, but easiest to check is the second solenoid down on the solenoid manifold under the driver's seat. It is a stack of five, mounted on the rear bulkhead and is a row of black solenoids identifiable by the red caps. This can be checked by listening for the valve to "click" when you select the front position on the rotary knob and then alternately press the up and down. In the "UP" position you will hear that valve and the one above it click, and in the "DOWN" position the second one down should click.

[HarborBus]

Thanks guys, I think I've got this(famous last words). It seems pretty simple to me, first I'll check the solenoid, as it seems the easiest, and if need be I'll replace it with one of the other ones to see if it is bad, failing that I will check the switch for continuity. Easy right? RIGHT.

[rodburtonmusic]

I just had to change that very same valve. Same thing...left and right worked great, front lift, nothing. It was an easy fix..even for me.

Where's the best place though to get additional valves like this? I happened to have access to an extra, but would like to have a few more on hand.

[HarborBus]

Rod,
What did you have to replace?

[rodburtonmusic]

Sorry..it was the norgren (sp) valve. The one that operates the up/down only. Very easy to swap out...once you isolate which one it is.

[Will Garner]

Rod,

If you can get an angle to take a picture it might help Harborbus find his.

Just a thought.

[Jon Wehrenberg]

Elliot, We are finally home and I can get back on the computer. Yes, by all means swap stuff around to isolate the problem. Anytime you have two or more parts and one of them is in a system that doesn't work switching parts around helps you find out which parts are OK by process of elimination, or which are bad.

The reason some coaches have four solenoids is because over the years both Prevost and the converters have made numerous running updates and changes to the suspension system. Hector's program that shows the workings of a system is generic, but the operating logic is correct, while the specifics are going to vary from model year to model year and converter to converter.

For anyone to have a perfect suspension system the only way to be assured of that is to actually ignore the operating logic and rebuild or replace every component after carefully bench testing all parts for leaks or proper operation. To repair the system, use the program Hector created as a guide to isolate only those parts that are actually associated with the defective part of the total system.

[HarborBus]

I finally got a chance to see if I could fix this problem. I have now determined that if I put the selector switch on the front position I can exhaust the air and the front goes down. Then I tried to raise it from that dumped position by pushing the up switch, nothing. Then if I put the selector switch to the off position the front will come up to, what I believe is, ride height. I removed the rear right solenoid and put it where the front solenoid is then I turned the selector switch to right position, pushed the up switch, nothing. What now, am I missing something?

[Jon Wehrenberg]

Elliot,

What appears to be happening is when your go to the travel or ride position the center solenoid is functioning as it should allowing aux air to flow through the ride height control valves.

When you go to the manual position and attempt to raise the front it fails because one of the top two solenoid valves or valve coils is failing to function. When you attempt to raise the front manually both of the top two solenoid valves come into play. My guess without getting further details from you is that the second one down is functioning correctly because the bus will go down, but the top one is faulty because it will not go up.

Since it appears the third one down is funtioning as intended don't change that one. It appears the second one down is also OK. So swap the top one with one of the bottom two and see if the problem with the front goes away. If it does you know what part has failed. If that does not solve it report back with details and I will go further into the system but right now my guess is with the solenoid valve or valve coil.

[truk4u]

Elliott,

I'll stay out of this since Jon is helping you, but remember, each assembly has two parts, the coil and valve. If your just swapping the coil and not getting any results, it could be the valve that is bad.

5765

[HarborBus]

OK Jon I'll try that, I sure wish I had an extra coil and valve on hand.:(

[garyde]

I finally got a chance to see if I could fix this problem. I have now determined that if I put the selector switch on the front position I can exhaust the air and the front goes down. Then I tried to raise it from that dumped position by pushing the up switch, nothing. Then if I put the selector switch to the off position the front will come up to, what I believe is, ride height. I removed the rear right solenoid and put it where the front solenoid is then I turned the selector switch to right position, pushed the up switch, nothing. What now, am I missing something?

Did you dump the front air and try to raise the coach again with the traded out coil and solonoid.

[Jon Wehrenberg]

OK Jon I'll try that, I sure wish I had an extra coil and valve on hand.:(


You do. Verify the rear left and right are functioning properly, and if so you know they are working. Use one of them to replace the top one.

Note Tom's post. Start by swapping coils.

[HarborBus]

Yes, I have verified that the right and left rear raise and lower as they are supposed to I have done it several times. So I will use one of those solenoids for in place of the top one. One question, is the auxiliary tank the little pancake tank in the compartment under the seat? If so how do I turn off the aux pump to keep it from trying to refill if I have to replace the valve. My pump for that tank is a 12 volt pump at the back of the generator.

[Jon Wehrenberg]

That's a Marathon question I cannot answer. I presume you can turn off the aux pump and bleed the aux air system down to zero if you have to change the valve and not just the coil. On my coach I have a connection for an air hose in that compartment as well as drain cocks on my pressure regulator bowl so I can dump air in the aux system at either place.

If all you change is the coil that has no impact on air pressure. Unless the Marathon suspension system is different than the Prevost Level Low (apart from HWH) dumping aux air will not change the height of the bus as long as the key is off, but anytime you are working on any part of the bus, either keep your body and all its parts out from beneath the bus, or support the chassis so it cannot drop.

[Kevin Erion]

you can turn that air compressor off at the small round circuit breaker back in the bedroom behind the dark plastic door. Look for the one marked aux air and push it, it should pop out, thats off.

[HarborBus]

Jon, thanks for all your help it has been raining here today so haven't gotten back to it, I'll see what the weather man serves up tomorrow.

Kevin, I have one that is labeled air compressor but when I push on the small round circuit breakers they don't pop out. It would seem that they should do something in order to turn off a circuit.

[Jerry Winchester]

Push it harder. It will pop out.

[HarborBus]

Jerry, Well done you are right, I pushed harder and they do pop out:o. This is going to be a loooong and painful exercise for the "brain trust" to bring me up to speed on this bus. We are leaving 11/1 for warmer country so I'll get to take stuff apart, panels off, and do some investigating.

Thanks everyone for all the help so far. Whats the quota in stupid questions, Like one a week, month.............?:rolleyes:

[Jerry Winchester]

No problem. If you had posted this after a couple of months, the answer would have been, "Put your man panties on and push it like a big dog not like Truk opening a new case of sheep".

You'll know when you reach the statute of limitations...............

[truk4u]

That was harsh!:rolleyes:

[dale farley]

Elliott, You're in luck. We all get at least one stupid question for each stupid response we are about to receive. The number of stupid questions never catch up with the stupid responses, so we never exceed our quota of stupid questions.

[Jon Wehrenberg]

All of us are still waiting to meet the new Prevost Conversion owner that has no questions. He is either a genius or a fool.

No matter how well you know your coach, no matter how long you have owned it you will still find stuff that was previously unknown. And the newer and more sophisticated the conversion, the more unknowns.

[HarborBus]

OK, here's the latest, it appears that all the solenoids are good. I switched out 1 & 2 and put in 4 & 5 No difference. Additionally with solenoid 1 & 2 in the rear positions I raised and lowered the right and left so I just left it that way. So I guess the only thing left is the valve or valves in one or two position. Would the spool valve have anything to do with that one position (front)?

[Jon Wehrenberg]

Yes. The only valve that appears to be not "shifting" is the three port valve. It should be located on the rear bulkhead of the lower steer compartment.

The valves are simple to work on. Take it out, remove the four screws from the end cap (either one), and carefully take the cap off. My guess is the plunger or the spool is stuck.

[HarborBus]

Everything works............... kinda. I can lower the bus with the switch in the front position and it will raise to ride height in the drive position. BUT, when I put the switch in the front position and lower it I can not raise it at all with the (up) switch. If I raise the tag I can raise the bus any height I want. Prevost says the pressure the tag is putting on the front impedes it's ability to rise. I'm not buying it because if that were the case It should not raise the front it to ride height in the drive position. I'm thinking the #2 valve has a small leak not allowing sufficient air pressure to raise it with the switch in the front position. What does the Brain Trust think?:confused:

[Jon Wehrenberg]

Without studying the circuits to refresh my memory I can say this. When you use the road height switch position aux air is directed through the ride height valve that is located top center over your steer wheels. The 5 port Norgren that controls that is "switched" by one of the solenoid valves in the stack located on the rear bulkhead in your lower steer compartment. If your solenoid stack is like mine it is the center solenoid switching the Norgren.

When you are manually attempt to control the height the top two solenoid valves (again, if your set up is like mine) are the controlling valves which shift the five port Norgren to raise the coach. When the command is to lower the front, only the second valve down is used, so check the top solenoid valve. I suggest you check the coil because my guess is the valve is likely OK, but the coil is bad. To verify this either check for an open circuit, or switch coils with one of the bottom coils temporarily.

[truk4u]

Like Jon said, it's one of these bad boys!

6501

[Jon Wehrenberg]

Elliot,

I presume by your October post you are familiar with the solenoid valves, that they are modular and that you can swap out the parts to eliminate or confirm you have a valve or coil problem.

If you have already gone through the swapping of parts to check operation of the solenoid valves the next step is to verify you are getting power to them. The coil is easy to check because you should have continuity. if you do not, it is bad. But one thing I should point out is that the generic Prevost leveling system may be modified by the converter to provide automatic features. My Liberty has been modified and some coaches have had a converter installed HWH system.

If your bus solenoid valves and coils check OK, then someone familiar with any system mods you may have may be needed to help.

I do believe the advice you were given about the tag is technically correct because when you lift the tag you transfer some front axle weight rearward making less pressure in the air bags required to lift the front, but the person that told you that ignored the fact the ride height valves were functioning so the problem you are dealing with is related to the manual controls. I still guess it is the solenoid valve or coil.

[HarborBus]

Thanks Jon, I'm going to check the coil on position #1 and #2. I did it back on October 27Th (see post #32) but I am more confident now so I'll check them again. I don't think there have been any modifications on my system, there isn't anything automatic about it at all. I bought a new coil and valve when I was at Prevost just so I'll have them. I'm busy watching the Masters Tournament today but I'll get to it tomorrow. Thanks again guys for the impute.

[gmcbuffalo]

Also check the voltage or that there is voltage to the solenoid valve coils. I had a problem at the selector switch, one dirty contact and it would not allow voltage to the coil to function.
Greg

[Jon Wehrenberg]

Elliott,

Since you apparently have no converter installed automatic leveling you should have the unaltered Prevost Level Low system. That will make trouble shooting less complex. I would suggest you just methodically start at #1 solenoid valve and after you replace the coil, or the coil and the valve you check the performance. By doing one thing at a time you will know exactly which component or assembly is the problem.

One thing everyone needs to keep in mind. If the bus ever fails to return to road height on coaches with the 5 solenoid valve assembly, the center valve is the control for all three 5 Port Norgren Valves which in turn routes air through the ride height valves. That is the starting point for diagnosis. That valve is always energized when the key is on and the selector is in the road or driving position. On older coaches with the four solenoid valve assembly I am not sure which one is the driving position valve, but it is important to know.

[treedoc]

When we were airing up at Heritage the front didn't come up. Air was leaking from no2 valve on 5 stack solenoid valve bank. So I aired down and tried again, everything worked this time. This morning same thing, so I replaced no 2 (second down from the top) valve in 10 minutes. luckily I had a spare on board. Rick