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Leveling System Condundrum - Printable Version

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+--- Thread: Leveling System Condundrum (/showthread.php?tid=3747)

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Leveling System Condundrum - bikestuff - 09-10-2017

Gurus,

I have had a weird leveling related issue for a while.  One of the senior gurus reminded me that collecting data is a valid way of isolating problems and identifying the likely cause.  This post is to document the data collected on my coach.  I present a problem and an approach to troubleshoot but not an answer.  (Because I have not figured it out yet).  

In a nutshell, the issue is that if I leave the coach in travel mode at full travel height, the coach stays level and does not leak down.  However, If my air bags are somewhat below travel height, they will leak rapidly down in the rear of the coach.  (For example if I auto level, or turn tightly where the HCV has let air out on one side, ...).

I have attached a document with three graphs of data collected over the past couple of days....The coach was parked on a reasonably level pad.  Measurements were made at the bottom of the body panels behind front wheels and the bottom of the body panels in front of drive wheels.

Three tests were run:

No Auto Level (travel mode).  The coach was put into travel mode and measurements taken over a 36 hour period.  

Auto Level On -> Off .  The coach started at travel height, and was then auto leveled.  Auto level was then turned off and measurements taken after 2 hours.

Travel -> Dump Air (No Auto Level) -> Off .  The coach started at travel height.  Air was dumped using the leveling system for 8 seconds.  Then the HWH was turned off.  Measurement was taken after 4 hours.


Observations:  

1)  The coach does not leak much in level mode with the bags full.
2)  Auto-level results in the coach dropped in the rear.
3). If I partially deflate the bags using the dump valve, the coach will continue leaking down to the bottom.  (This is with the key off and with auto level turned off).   
4)  With the key off and auto level off, the coach should maintain its height, but does not. 
5) The leak appears to be in the rear air system.
6)  When the leak is present, both the left and right rear air bags seem to track each other.  
7)  The leak down is not related to the auto-re-level logic because auto level was turned off in each scenario.

Next steps....  
1) Adjust the mercury switch so that auto-level results in an initially level coach.  I will do this by using a 4 ft level to manually level the coach, then will zero out the mercury switch.
2)  Since the problem seems to be related to the amount of air in the bags, I will replace the HCVs.  My HCVs are original in the coach and I really just want to replace them for general purposes.  I will try the tests again with new HCVs.  In the meantime, I will use my isolation tool to try to isolate any leaks to the 6 pack solenoids or downstream air bags.
3) I will also repeat scenario 2 (partial air in bags) and see if I can detect a leak with my sonic leak detector.

Cheers,
bill

RE: Leveling System Condundrum - Richard - 09-10-2017

Let me add, before it is asked. All of the leveling was done with the ebrake off. Bill has demonstrated without a doubt that the ebrake will hold the suspension up when the coach is leveled. His coach jumps even more than Tom's when the ebrake is released.

RE: Leveling System Condundrum - 77newell - 09-10-2017

Question: what "SUPPLY" air pressure is present during these tests?

Question: after you dump for 8 seconds, what happens if you place the system in "TRAVEL"

RE: Leveling System Condundrum - bikestuff - 09-10-2017

Jon,

Supply air is the engine air supply. (At least initially. When I turn off the HWH, I also shut down the engine). I will verify the amount of air...but I don't have any trouble getting to travel height.

I did not put the system in travel after dumping air, but in each case I was able to return to travel height within a few minutes.

bill

RE: Leveling System Condundrum - 77newell - 09-11-2017

Thanks Bill. It sounds to me as if your travel valves might be remaining open all the time or much of the time despite the settings on the control panel. If the HCVs are at travel height they are closed and would lock the current air pressure in the air bags even if the travel solenoids are open. If they are below the set height they will try to add air from the SUPPLY air pressure, if that air pressure is below that needed to raise the coach then the air bag pressure will flow backwards through the HCVs to the SUPPLY tank, this will only happen if the TRAVEL solenoid valves are open.

My thoughts are to do a couple things. First, do not replace the HCVs unless they are proven to be a problem until after this "dropping" problem is solved. Changing parts can cause new problems to arise which will just complicate finding the current problem.

Second, use Richard's famous solenoid valve test to check if they are energized by placing a screwdriver tip on the center post of each and see if you detect the pull of magnetism. Do this in first in the travel mode to see what it feels like and then after dumping or any setting you have used in this testing process other than TRAVEL. While you are at it, also check all the other solenoids to see if they are acting according to what you would expect. This test will verify whether the electronic control brain is working correctly.

If nothing shows up in the electrical test, then I would pull the lines coming from the HCVs to the travel solenoids to see if air is flowing out of those solenoids toward the HCVs. Do this test in any mode other than TRAVEL. This will test the mechanical integrity of the travel valves.

What I find strange about your situation is that the whole of the back drops together. Given that this problem started suddenly and has been consistent leads me toward a single component failure causing the symptoms you are experiencing. So, we are searching for a single component failure that can cause both sides to drop at a similar rate. The only single component that I can think of that could effect both sides is the electronic controller for the leveling. The odds that both travel valves or both HCVs would fail exactly simultaneously seems incredibly small.

I hope this is helpful to you

RE: Leveling System Condundrum - bikestuff - 09-11-2017

Jon,

I tested the solenoids with the "Richard trick" and found that the travel solenoids are energized in travel mode and not energized otherwise.

This problem was not sudden onset...It has been here for quite a while....but indeed both sides drop together.

One thing that I did not say in the introduction is that this coach has a bunch of miles (240,000 + 15 years old)....Waay past the expected life of an HCV. Could it be that both HCVs are just plain worn out and have some sort of dead spot where they both leak? I think that I would also have to have bad solenoids for the bags to leak even with leaking HCVs. That sounds like a very unlikely coincidence.

I will pull the lines to the travel solenoids next.

Thanks!

RE: Leveling System Condundrum - 77newell - 09-12-2017

Yeah Bill, to have 4 things fail at the same time seems highly unlikely. And as you say, even if the HCV's failed they should only allow air to leak if the travel solenoids leak when they are supposed to be shut. The HCV's could be leaking SUPPLY air all the time but that should not effect the air bags whenever the TRAVEL solenoids are closed.

Let me think this through out loud. The air bags have relatively high pressure in them +90psi in my 93 single axle coach. So, if the rear is dropping, that air pressure needs to be leaking to some place that is lower in pressure, either the atmosphere or to the SUPPLY tank if it is less than 90psi. We believe the bags themselves and the lines to them are not leaking because there are times when they hold up just fine. The thing that stands between the air bags and the places of lower pressure is the 6 pack. So, let's take the solenoids one at a time.

The "Raise" solenoids, if leaking, could drop the rear, but only if the SUPPLY tank was less then 90psi and would tend to raise the rear if much above 90psi. The raising part doesn't seem to be happening so we can rule that out.

The "lower" solenoids, if leaking, would drop the rear in all the time and would be compensated by either the HCV's in the "travel" mode or by the "raise" solenoids when activated. We can test if that is happening by applying soap bubbles to the vents at the 6-pack. This failure seems unlikely since I think you described no dropping occurred when going from "travel" to "off" at the control panel. Still, since soap is cheap and easy it's worth verifying.

The "travel" solenoids, if leaking, would drop the rear only if the HCV is either above its set height or if it was below its set height and the SUPPLY tank is less than 90psi and air would then go backwards into that tank. One other way to test this besides pulling the travel air lines at the 6-pack would be to dump the rear a bit, go to the "off" mode on the control panel and ensure that the SUPPLY tank stays above 100psi. If the "travel" solenoids are leaking the rear should slowly rise as the HCV tries to get back to its set height.

The added conundrum is that both sides seem to be dropping at about the same rate so whatever leaks exist must be nearly identical, not likely due to wear or holes.

I'm beginning to fear that all these tests will prove negative and we have a logically impossible problem. If that is the case, I'm looking in the wrong place, because all these problems are ultimately logical. Hmmm. Where else might I look. The only other support of the rear of the coach is the tag axle. I don't have one so that has just now entered my thinking. So, now I'm thinking I would put a pressure gauge on either of the lines from the 6-pack to air bags and know for sure the dropping is due to lowering pressure in the air bags. If the pressure is dropping I really need to put my thinking cap on tight. If the pressure is NOT dropping then I would start looking to the tag axle suspension system. Geez, I love my "simple" system.

Bill, sorry I can't be more definitive, but given that you seem to have a logically impossible problem .....

RE: Leveling System Condundrum - bikestuff - 09-12-2017

Jon,

Thanks for the thoughtful analysis. I really appreciate it.

I think I caught the system venting with the key off and not in auto level the other day. The venting was between the drive and tag axles on passenger side.

I am at the factory and will be on the pit tomorrow for a non related issue tomorrow (I think). If so, I will put the coach in travel, dump some air and see I can repeat the problem. To add to the description. If you look at the graphs, it does not take long at all to lose all the air in the bags when the problem is present. I am hoping for a little luck in being able to hear the leak when I can get under the coach.

If that does not work, I will start measuring air pressures at the six pack.

bill

RE: Leveling System Condundrum - encantotom - 09-12-2017

bill, i learned something yesterday that at first caused me some consternation. i was at leo's getting my front airbags replaced. after we got them in we wanted to fill them with air before totally tightening the mounting bolts so they could "self align and untwist" .

i turned the key on and tried as i might to get the hwh control panel to light up. to no avail. it would flash all lights then go dark. since the front end was raised up alot, it did show at first the excess angle light. so i could not get any air to air up the front airbags.

leo and scratched out heads wondering what was going on. then i thought to myself.....the parking brake is off. leo likes it off when using the lift. i put the e brake on and walla, everything worked. i just never thought about it before. and for sure never tried to use the hwh control panel with the ebrake off. ya gotta have it on for all this to work.

tom

RE: Leveling System Condundrum - bikestuff - 09-12-2017

I failed to say this...but for my tests I had the eBrake off. I have a switch on dash labeled: Leveling Override. With that switch ON, you can use the HWH without the brake on.