[Archived]

Chuck,

First, your vintage Liberty may not have the switch positions the same as later models. Like Prevost the design of the system modifications Liberty makes may have evolved making any advice we offer inaccurate.

I think the first thing you need to do is verify the switch positions and functions. The switches that control the individual locations should be bottom down is to lower, center is off and top is raise. Play with the switches until you are satisfied you know what position does what. That can be part of the problem.

On that vintage your automatic leveling may function with the key off. Verify that also because if the main switch is left in that position, just walking around inside the coach causes the system to constantly take on and exhaust air. The solution to that is to level the coach with the engine running and as soon as it is level, and all pressures are at their max, simultaneously put the main leveling switch in the road or driving position, while turning off the key.

Your vintage has the Prevost system logic that requires 30 to 35 PSI in the aux air system at all times minimum otherwise tag axle air is dumped and that will result in the coach going out of level.

So before we can offer a best guess as to where to look for a problem you need to verify how your system works

[Jim]

Jon, thanks, I will go over it and identify the function of each of the switchs & positions. After I posted my first note I realized I was not as complete as I should have been in the description of the problem. Some times when I park the coach with it all the way up on air it will sit for days and not lose any air. I need to park it with the air all the way up with the switches in different positions and see if I can figure out what positions the switches are in when it bleeds off air. As soon as I get this figured out, along with your questions, I will let you know what I find. Thanks again for your help.

[Bryan]

Chuck I would run your bus up as height as it will go and block it up with supports and go under it with soapy water solution and look and listen for leaks. Looking at the pneumatic diagrams for your bus I think your system is a liberty system and they would be a go place to start with phone calls.

[Archived]

Greg,

I disagree. While at some point going beneath the coach with soapy water might be part of the solution, the first step is to understand if the switch positions are contributing to the problem.

My 87 Liberty had the automatic leveling position enabled with the key off. That alone will bleed air from the coach and with the system logic of the Prevost level low of that vintage once aux air hits 35 PSI tag air will dump and the coach will no longer be level. The coach is doing exactly what it is supposed to do. Walking around inside the coach or sidewinds will have an impact.

So step one is to learn what each switch position controls and once that is know then it becomes easy to determine if the coach has a problem, and if so, what the problem is and where to look.

[John]

Greg, thanks for the input but I agree with Jon (albeit for a different reason). I’ m 74 and had my previous coach damn near crush me so I don’t get under them any more. Jon, I am in the process of running several tests to see if the coach reacts differently depending on where the switches are set. I will try to have some accurate measurements in a couple of days. Thanks for sticking with me. Intuition tells me my system is the one installed by Prevost but that is just a guess. I Will let you know what I find in a day or so.

[Archived]

Jon and Chuck I agree with you on the switches. I went to the Prevost site and I could see no low level function in the schematics so I assume two things. One it is a liberty set up and two the switches were working based on how I read the original post. Therefore I thought we were dealing with a air leak issue.

[John]

Chuck, just to be clear your first step is to verify what each switch does in each of it’s positions. For example if the switches are installed by Liberty you are going to have one switch that controls the road or driving position, a manual position and an automatic position.

The road position causes the coach to set its height relative to the ground and is the position the switch needs to be in while driving. The manual position is the only one that enables the other three switches which control the up and down commands for manual leveling at the front, LH and RH rear. The automatic position levels the coach and does it without any input from you.

If you have the standard Prevost level low I believe you will have a rotary knob with 4 positions, one for driving, and the other three for the front, LH and RH rear. When the rotary switch is in any of the three manuial positions a rocker switch can be used to make the selected position go up or down.

Step one, determine what you have, and step two is learn and verify what each position is and does.

In the case of the switches being the Liberty type which eliminates the rotary switch and instead uses a total of 4 rocker switches you also have to determine if the functions are enabled with the key off.

[Jim]

Jon

Ok, let’s see if I can better describe my leveling system and the problem. My system operates with the key on or off & with the cranking batteries connected or disconnected. The system is controlled by four switches just to the left of the driver and each has three positions – up, mid and down. The switch functions labeled from front to back are OFF, FRONT, RR & LR. One click down for the switch labeled OFF ( this switch controls the Level/Low light) puts it in the manual position and the lower most position or two clicks puts it in the auto position. The switches labeled Front, RR and LR I assume are in the ” over the road” position when all the way up, one click down is “raise” and two clicks down is “lower” and their function is controlled by the front switch labeled OFF or Level/ Low. When I am driving I have all four switches in the upper most position which keeps the bus up on air and level while traveling, with a soft, comfortable ride. Typically when I park the coach I level it by putting the main switch (Level/ Low) in the manual position and use the Front, RR & LR to level. Once level I put all of the switches in the top position, which I believe is off, and the key is off as I am parked.

Tests – key off and cranking battery disconnected

Test # 1. I brought the bus all the way up on air and then put all four of the switches in the upper most position. Over night the driver side rear dropped all the way down. The front and right side stayed up.

Test #2. Again the bus was all the way up on air. I put the Front, LR & RR in the top position (off or over the road) and put the Level / Low switch in the manual position. Again the left rear corner dropped.

Test #3. Bus all the way up I put the Front, LR & RR in the raise position ( one click down) and the Level /Low in the off position. Less leakage over night.

I don’t know if the problem is with an air bag (all are less than two years old), an air line or a control valve or……? I don’t hear any leaks at the “dump valves” in the compartment under the drivers feet. Do you know when leveling if I am controlling air in both the drive and tag axel air bags?. Any thoughts will be appreciated. Thank you

[glen]

Chuck, The picture is now a little clearer.

You can confirm this, but let’s you and I start by using the same terminology so I know we are connecting.

The three switches labeled front, LH and RH only should only function when the “master” switch is in the “manual” position. We’ll call them “position” switches. You will know when it is in the manual position because the level low indicator will be lit and all of those position switches will make the coach go up or down. It does not matter for purposes of this discussion that I understand what each position of those switches does what, but it is important for you to understand which position makes the coach go up, down, or do nothing (the “off”) position.

When the master switch is on the “automatic” position if the coach is not level, it will level itself. You can prove this by putting the master switch in the manual position and raising one side and lowering the other, then go to the automatic position and wait for the coach to level itself. The level low light should be on and none of the three position switches will function when the coach leveling system master switch is in automatic position.

Finally, when the master switch is in the road or driving position the level low light should go out, the bus should go to the driving height and none of the three position switches should function.

You can verify all of this.

Now to solve your problem. Put the coach master switch in the driving position. I don’t care what position the “position” switches are in because if my description above is correct they are not going to function. With the bus in the driving position or height let it sit. If you can periodically check it just keep track of movement. A tape measure used at four points at intervals will help. What I want to know is if the coach gradually leans or if it stays where it is for a while and then leans somewhat suddenly. If you have a gauge record the auxiliary system pressure. If you don’t have a gauge you might be able to read it at the Schrader valve in the steer compartment.

You either have a leak specific to the LH rear or your aux system is bleeding pressure overnight and once it drops below 35 PSI or thereabouts the tag axle air bags dump air. Once we know what is happening we will also know where to look and how to correct the problem.

From now on, when you leave the coach, even if you have leveled it, return the master switch to the driving position and immediately turn off the key.

[Bill]

Jon, I will run the tests you suggested and be back in a day or so. I know with the master switch in the ride position it drops, I just dont know how fast (whether it is a slow leak or the tag dumping), I will set it up and measure it multiple times over several hours.

In paragraphs one, two and three of your note your comments are correct and I understand the functions. Thanks

[Bryan]

Chuck, until you get some more info I will toss out what I think causes the leans.

I believe you have two issues, neither of which are as pleasant to solve as having root canal work.

As our coaches age we start to experience air leaks. The more complex the coach aux air system, the more leaks there are to chase. You may have one or two easily identified leaks, but in my experience most of the leaks are relatively small, but when you consider the total leakage they amount up. Your coach, unless modified has the logic in the leveling system that requires aux air pressure to be maintained or the tag axle air is dumped. When that happens one or both rears will drop. Don’t ask why sometimes only one side drops because I have never figured that out.

The second problem is you are also likely to have a leak in the LH rear but the good news is that is likely to be isolated to the three air bags on that side, the fittings, or the five or three port Norgren valves.

I see soapy water solutions in your future.

But let’s get some results and maybe we can narrow it down.

One thing everyone should note is that chasing leaks has to be considered a hobby. If you treat it like a repair and turn the coach over to someone to find and fix the leaks that is akin to giving them your wallet, checkbook, credit cards and password. In days gone by some owners have reported techs working three days with squirt bottles of soapy water and multiple valve, fitting and air bag replacements, only to get home and wake up to a coach leaning over in the driveway.

We got your back on this one Chuck.

[Jim/Chris]

Jon, I think I am in information overload. Here are some measurements and thoughts.

Time. Aux air lbs. L Rear. L Front. R Front. R Rear

Lbs. Height. Height. Height. Height

2:30. pm 110. 45. 43. 42. 44

3:00. ” 80. “. “. ” “

3:30. ” 60. “. “. “. “

4:30. ” 20. “. “. “. “

5:00. ” 0. 43. 43. 43. 43

5:30 ” 0 ” ” ” “

8:00 ” 0 ” ” ” “

8:00. AM. 0. 40. 41.5. 44.5. 43

When I put the bus up on air at 2:30 Yesterday afternoon I used the aux air compressor and also had the engine running so my brake air pressure came up to 100 pounds. I heard an air leak and stuck my head in the compartment under the drivers feet where the equivalent of the master cylinder is and found an air leak at the bottom of the master cylinder “bendix valve ” that is operated by the brake foot treadle. By 5:30 my brake air pressure had gone from 100 lbs to zero. If I understand correctly, the brakes have primacy in the air supply system and in the event of an air leak in the brakes the aux tank and the air bags will back feed in an attempt to maintain brake air pressure.

When the aux air dropped below 20 lbs ( at about 4:30) I heard air escaping as if it was dumping and the pressure went to quickly to zero but the bus stayed level. When the aux air dropped to zero my tag axel warning system (buzzer and light) came on but the bus is stayed level and only dropped negligibly.

Overnight it dropped in the left rear and I am having trouble getting the left rear tag to “air up”.

I think you are right that I have multiple problems. One is clearly the brake valve, second I think is the LR tag dump valve (it appears to be the only one that dumps when the air gets low in the aux tank), and who knows what else. Any other thoughts will be appreciated. Thanks a lot

[Archived]

Only some aux air systems will back feed to the brake system and without looking at the schematics I do not know if this is by design or because a system check valve has failed.

But regardless your primary systems need to be leak free. I realize the DOT brake check permits a modest leak rate, however on all my coaches the brake systems would hold pressure for weeks if not months. When the coach is parked and the emergency brakes are applied there are only a few places you will have pressurized air and all are easily checked. You already know the treadle has a leak so that alone may be your sole source of the brake system air leak.

I’m not comfortable saying right now that your treadle leak is also bleeding down your aux system. Regardless you now also know when the aux system gets below a certain pressure the tag axles dump air. That is expected.

Until you get the brake system somewhat leak free and / or stop the aux system from losing air through that point (if it is) you are going to find it difficult to isolate the source of the leans.

Here is something you can try. First, understand that the purpose of the 5 port Norgren valves is to “lock” air into their respective air bags when the key is off and the switches as I described previously. But since your air has an escape path in the rear via the tag axle air dumping, let’s eliminate that in a test. Raise the rear of the coach as high as possible and raise the tag axle. Be patient. You want the coach as high as possible and all the weight off the tag. This should now lock the air in only the drive axle air bags, while dumping tag axle air. Leave the tag lift lever in the lift position. When you are as high as the coach can go and the air pressures are at max (120 to 125) move the master switch to the road position and simultaneously turn off the coach.

Now if the aux air goes to zero you won’t be dumping tag axle air because it alread has been dumped so the axle can be raised. If the 3 and 5 port Norgren valves are leak free and the bags and fittings are leak free the bus should not lean.

Do you work on your own coach? If so do you have a means of supporting it?

[AL]

Jon, I do work that does not require getting under it. I’m to old (74) and it is just to dangerous for me. I will try the test you just suggested ( raise the rear….) and let you know what I find. Thanks for sticking with me. I really appreciate the help.

[Kenneth]

Chuck,

Where are you located? Getting under a coach is not dangerous if the chassis is supported properly. I am concerned about how difficult it is and expensive to find someone to chase down the problems.