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Thread: 1997 40 foot xl ride height question

  1. #1
    Join Date
    Mar 2017
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    Kerby
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    Default 1997 40 foot xl ride height question

    I found old posts about raising the front end above ride height being difficult and taking a long time unless the compressor is set for 120 to 125 psi cut off. Mine sneezes and cuts off at 116# to 117# indicated on the two mechanical pressure gauges. The gauges on the Silverleaf glass dash read 10# lower than the mechanical gauges all the time. I had the air dryer serviced (removed, cleaned and cartridge changed) last March. Sneeze and cut off pressure was the same before and after this service.

    This bus has independent front suspension, the first year as I understand it. Chassis is a 1996. In the old posts some suggested raising the tag to get the front end to rise, others said that was not necessary if the system worked properly.

    My bus seems to reach ride height quickly enough but struggles to go higher in front if I need to raise it to level while parked. Sometimes it will, sometimes it won’t but is always slow. Is this an indication that one of the Norgren valves is crudded up or just that the pressure cut off point needs to be adjusted up to 125#? If I do need to adjust the pressure upward how do I do that?

    thanks. Jerry
    Jerry Work
    Kerby, Oregon
    1997 Prevost Country Coach
    40 foot, no slides, 100k miles
    Now after one year 110k miles

  2. #2
    Join Date
    Mar 2013
    Location
    Chicago
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    2,079

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    Before changing anything try this. Without going into high idle, first pump the brakes to get the compressor running then when it's 100 psi and headed north get on the up button in level low front and hold it until the air dryer sneezes. Note and post the results.

    U have an XL and probably do not have an aux air Guage and u should because u would be amazed at the pressure differences when the brake tanks say 120 and your on the up button without the compressor running.
    Last edited by Joe Camper; 10-10-2018 at 11:10 AM.
    1990 Peterbuilt 377
    3406 B Caterpillar
    9 Speed Roadranger
    708 243 7871

  3. #3
    Join Date
    Oct 2012
    Location
    Smithville
    Posts
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    Hey Jerry,
    I have a 1995 Chassis / 1996 Liberty XL40’. And My Aux pressure is set @ 45/70, And the front will raise pretty quick in manual. For those that suggest you raise your pressure on the aux system to 120-125. I hope they have a good up to date water separator system installed. The Aux compressors are notorious for making lots of moisture. Might be different on the CC, But all I need aux air for when the coach is turned off. Is the bathroom pocket doors and the waste tank dump valve and the gen air bags if I need to run gen. I do turn the aux compressor on to tighten belts before starting main engine. Then the main engine compressor will take over and supply pressure to the aux system. Air seat , floor slide , horn , belts , gen air bags , dump valve , Forward shutters , and door lock. I agree with Joe on adding the Aux gauge. I added one and it has been very helpful.
    My Wife said " You have Gone Crazy " When I purchased the Coach. Now She says , " DONT SELL THE BUS"
    ​Email; libertycoach322@gmail.com


    Safe Travels,
    Rocky

  4. #4
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    Mar 2013
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    Chicago
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    Rocky u got a straight axle don't u? His suggestion or question about bumping up the air pressure wasn't with the auxiliary compressor it was with the governor on the engine.

    If he were in an XLV or even heavier yet and XLV double slide I definitely suggest he'd turn that up to 125 but since he's only got a 40 foot nonslide even though it is a tick low at 117 it still should be enough to raise the front end if he uses the process I told him.

    The suspension gets its air from the auxiliary tank but the governor on the engine is triggered from the pressures in the brake tank. On some chassis not all but on some if you're at 120 on the brake tanks and the compressors idling the air dryer has kicked out and you go to level low and you try to go up if you had an auxiliary air pressure gauge what you would see is the auxiliary tank pressure drop all the way down to below 90 and stay there but the brake tanks are still up at 120 and the air compressor won't come on and you stall out because the front end needs over 95 PSI to get above ride height with IFS. Pump the break a little bit and get the brake tank pressure down under a hundred and get the compressor going and then all three tanks equalize come up to 120 together.

    Up ve go.

    I suggest not doing it on high idle leaving it on low idle because some of the suspensions react so slowly, because some of the steer axles are so heavy, You Know Who You Are, if it's on high idle the air dryer sneezes again before you get to Max height so be patient, do it just idling.

    The guys with the aux air tank guages can see it all happening. Without one and not enough understanding u think somethings wrong.

    In the real world usually you're not trying to get above ride height in the front all that often so in the big scope of things even though it's lacking there a little bit on some chassis it's really no big deal just use my method when u have to.
    Last edited by Joe Camper; 10-11-2018 at 03:47 PM.
    1990 Peterbuilt 377
    3406 B Caterpillar
    9 Speed Roadranger
    708 243 7871

  5. #5
    Join Date
    May 2012
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    Beverly Hills
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    What pressure to set your converter's aux compressor to is a topic of debate. First, this could be an setting for the compressor or a setting for the regulated output of the compressor's storage tank.

    I don't support setting the air compressor to low settings. I recommend setting them to 10-20 psi lower than their factory setting up to a maximum of 110psi. This should give you the maximum air storage without having your compressor over work itself as it ages. A higher pressure reduces the frequency of running. Yes, it will run longer when runs. Less frequent cycles should also reduce the possibility of wet air leaving the storage tank.

    As for regulating the output of storage tank, I don't see any value in doing so.

    Ideally, you don't need to run your aux compressor when the engine is running. If you have the one converter that requires the compressor to stay on you might want to consider a check valve so your Prevost air supplies all coach air requirements when the engine is running.

    When a coach is parked, the aux compressor should be limited in what it supports to reduce cycle frequency. This is not always possible.


    Gil and Durlene
    2003 H-3 Hoffman Conversion

  6. #6
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    So Gill help Jerry get his silver leaf get to the same pressures as the mechanical air gauges, like they should. Thats no good.
    Last edited by Joe Camper; 10-11-2018 at 03:52 PM.
    1990 Peterbuilt 377
    3406 B Caterpillar
    9 Speed Roadranger
    708 243 7871

  7. #7
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    Jerry,

    Put a gauge on the air lines at the SL transducers in the driver's bay and see if SL is correct. If not, there may be a calibration setting in the dash. It's been too long for me to remember. If calibration is necessary, a quick call to SL should get you the answer.


    Gil and Durlene
    2003 H-3 Hoffman Conversion

  8. #8
    Join Date
    Mar 2017
    Location
    Kerby
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    Thanks for all the suggestions. I will try them today and report back. Through this process maybe I can better understand the interaction between the Prevost engine driven compressor and its two air tanks, the aux compressor and the level low system. So far I have only used the aux compressor before cold start in the morning to tension the belts and for airing up tires. With no slides and no interior air doors there is not much need for air when parked. The coach does not leak down over night, but will leak down all around over several days. It comes to ride height quickly and easily. The only issue is raising the front above ride height when necessary to level. The auto level function appears to work correctly otherwise.
    Jerry Work
    Kerby, Oregon
    1997 Prevost Country Coach
    40 foot, no slides, 100k miles
    Now after one year 110k miles

  9. #9
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    Mar 2017
    Location
    Kerby
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    Here is what I leaned today. Aux turned on and at 120, engine on, both air gauges move up. At 100psi indicated I pushed the up/front button on level low. Hold that for three minutes. Pressure reaches 117 F&R but front end does not come up. Press brake, pressure F&R falls to 95psi and comes up[ to 108 F/R with up/front button pressed. Does not go any higher after 2 more minutes. Go to high idle, no change. I know from experience that pressure will go up to 117 F&R as soon as I start driving.

    Put tag axle up and front rises 1" but won't go up any further. When I drop the tag axle the front drops 1" and stays there.

    In all cases, as I release the level low front up button I can hear a momentary air release from the DS front steer compartment. Sounds to me like the LL front/up control is not allowing air to enter the front air bags. They do appear to get air from the auto ride height system as the bus comes up to proper ride height and stays there while driving and for at least an overnight while parked. I don't know what caused the momentary air release sound when i release the front/up switch with the LL knob in the front position.

    I have not yet talked with Silverleaf about calibrating the dash to match the mechanical gauges. Will do so later today.

    Suggestions? Actions to take now?
    Jerry Work
    Kerby, Oregon
    1997 Prevost Country Coach
    40 foot, no slides, 100k miles
    Now after one year 110k miles

  10. #10
    Join Date
    May 2012
    Location
    Beverly Hills
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    To test Level Low, lower the front end and then raise it. If it moves in both directions, it's working. The short burst of air is normal.

    I'll defer to Joe on why it won't go higher. BTW, how high are you expecting it to go? The added height above ride height isn't much.


    Gil and Durlene
    2003 H-3 Hoffman Conversion

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