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Thread: Front won't go up or down?

  1. #1
    Join Date
    Jun 2009
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    Gig Harbor, WA
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    340

    Default Front won't go up or down?

    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?

  2. #2
    Join Date
    Jan 2006
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    anytown
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    8,908

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    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.

  3. #3
    Join Date
    Jan 2006
    Location
    Alexandria
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    2,161

    Default

    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


    red.png

    Mike

  4. #4
    Join Date
    Jun 2009
    Location
    Gig Harbor, WA
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    340

    Default

    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.

  5. #5
    dreamchasers Guest

    Default

    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/...hlight=airbags

    I hope this helps.

    Hector

  6. #6
    Join Date
    Jul 2007
    Location
    East Texas
    Posts
    946

    Default

    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.

  7. #7
    Join Date
    Jun 2009
    Location
    Gig Harbor, WA
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    340

    Default

    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.

  8. #8
    Join Date
    Jun 2009
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    Gig Harbor, WA
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    Default

    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?

  9. #9
    Join Date
    Mar 2009
    Location
    Harrison
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    623

    Default

    Quote Originally Posted by Jon Wehrenberg View Post
    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.

  10. #10
    Join Date
    Jun 2009
    Location
    Gig Harbor, WA
    Posts
    340

    Default

    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.

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