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View Full Version : Left rear of Prevost coach sinking overnight



503rdPIR
10-05-2017, 05:06 PM
I would like to begin by thanking Gil for the seminar at Santa Fe and for all of the useful topics that were discussed and also for walking me thru many of the items and systems on my own coach. Now for the problem with the air system on our coach which is a 2000 Prevost and a 2001 Liberty conversion. I discussed with Gil the fact that the right rear of the coach is losing air and "sinking" overnight and he recommended that I level the coach and raise the tag axle to see if the coach still dropped. I raised the tag axle after leveling the coach on each stop on the way home and experienced no leaking or sinking. What does that rule in or rule out as far as the source of the leak is concerned? If you are reading this Gil, I failed to ask you to elaborate at the time and didn't have a notebook with me to write everything down, so I probably would have forgotten it anyway!! Thanks again.

Don Rice

TheGadgetGuru
10-05-2017, 06:07 PM
If you are reading this Gil, I failed to ask you to elaborate at the time and didn't have a notebook with me to write everything down, so I probably would have forgotten it anyway!! Thanks again.

Don Rice

I learned that when Gil is giving walk-throughs, run a video camera. Heck, run two of them!

dale farley
10-05-2017, 07:48 PM
Don,

Based on similar problems others have had, it sounds like your Norgren valve to your tag axle is bad. Gil is probably still on the road, but I'm sure he will respond pretty soon.

Joe Camper
10-06-2017, 06:49 AM
The 2 position 3 way norgren OR the tag air bag, or both.

Gil_J
10-06-2017, 09:26 AM
Joe is the man when it comes to leaks. It goes without saying that 15+ year old push-on fittings are also suspect.

The reason to lift the tag is to help narrow down your search. Just make sure you've given the coach at least the same rest time you did before you lifted the tag. If it took 3 days, as example, for the coach to lean with the tag down, give it at least 3 days with the tag up.

503rdPIR
10-06-2017, 04:43 PM
Thanks to both Joe and Gil for the feedback. The coach was leaning overnight with the tag down and now stays level with the tag up for greater than 24 hours. I assume the norgren valve that may be suspect is one of the two rear norgren valves and most likely the one on the right - would that be correct? I'll also take a look at the tag bag and the fittings going to it.

Joe Camper
10-07-2017, 07:18 AM
The suspect norgren would not be one of the two that are on the wall forward of the drive axle. The suspect norgren would be on the in side of the frame rail between the two axles on the side that's leaning. Directly above the rear bag for the drive axle on the side that's leaning the air line coming off the rear bag on the drive axle on the side that's leaning go straight up into the norgren that could be making it lean. U will not see it without supporting the bus and getting beneath.

Faedtrig
10-07-2017, 10:52 AM
Hello, I am having a similar problem. I can set the level switch and it will level out. About 15-20 minutes later the solenoid that let keeps air pressure on system will lose power and the right hand side of 1999 Prevost Country Coach will drop. It appears to me that maybe a check valve is not holding. The fight side of coach stays up. Is there a check valve to maintain the pressure after the air pressure applied drops out. Thanks if anyone knows what to do.

503rdPIR
10-07-2017, 01:47 PM
Thank you Joe for the information. I will get under there and check it out today.

Joe Camper
10-07-2017, 05:32 PM
Hey John, welcome to POG. I was in SC about a week ago.

If u r using the HWH to level it see if it will remain level at ride height after u shut it off without trying to level. Will it still roll over?

Faedtrig
10-08-2017, 08:16 PM
Hello Joe,
The coil that switches the norgren valve that supplies air to the left rear loses its signal and removes the pneumatic signal to norgren valve. This allows valve to switch to exhaust port and left rear goes down. Wire 132E is what supplies energy to the solenoid. I have attached an electrical drawing of what is happening. Thanks for your help.14630
When key switch is on this coil stays energized and lets the coach go to the drive position. As soon as you turn key switch off the coil losing it signal and air exhaust via the norgren valve.

14631

Gil_J
10-08-2017, 10:20 PM
Hmmm, when you turn off the key port 3, drive height, does lose power, but should lock the air in the system. BTW, without a drawing in front of me, I'm pretty sure there is a check valve at the input of each ride height valve. If so, air could not come back through the level low manifold, port 3.

Joe Camper
10-09-2017, 07:32 AM
When u develop a lean it's hard to to diagnose when using HWH. Use prevo level low when leveling during diagnosis.

If your bus is dropping key off the problem is the norgren at that corner.

GoneCrazy
10-09-2017, 09:13 AM
When u develop a lean it's hard to to diagnose when using HWH. Use prevo level low when leveling during diagnosis.

If your bus is dropping key off the problem is the norgren at that corner.
Joe,
How bout on a 96 Liberty that has the 2 - 3 port valves in the drivers bay floor in front. That control right and left rear raise and lower in manual mode ? My left one is leaking out of the exhaust port and coach will lean to left. After turning key off.
That valve should lock up and not allow any air to escape when in Drive mode or key off position, correct ?

Faedtrig
10-09-2017, 09:15 AM
Hello Joe,
As soon as the coil that delivers pressure to the norgren valve that provides pressure via the compressor to the left rear air bags, the coach drops on left rear corner. The coil dropping out causes the valve to shift to the exhaust port. This is a three port two position valve. I can't figure out why the coil is losing its signal. Do you think the coil is bad and pulling too much current? I will send you a copy of the electrical schematic. Thanks for your help.14632

Faedtrig
10-09-2017, 09:19 AM
good morning Gil,
It appears the right side is locking in. The left rear is not, no leaks except the norgren valve in the cabinet below the drivers seat. The coil that keeps the system supplied with pressure is losing its signal to stay energized. This allows the norgren valve to shift back to spring side and exhaust air via the spring side of valve. I have attached a schematic of the wiring.14633

Faedtrig
10-09-2017, 09:27 AM
Should there not be a check valve in the system to prevent the loss of pressure when this coil losses its signal?

Gil_J
10-09-2017, 09:46 AM
All of the coil packs are deenergized when the key is off and you are not pushing the up our down button. The air solenoid under the coil packs are what kicks the air while inn level low. It sounds like the you have a leaking solenoid associated with that height control position.

Faedtrig
10-09-2017, 10:48 AM
Hello Joe,
wire 132E loses energy and allows coil to de-energize. When coil de-energizes the signal for norgren valve that controls the leveling of left rear switchs and valve exhaust air from that area. See drawing.14634

Gil_J
10-09-2017, 08:58 PM
Rocky,

Can you figure out why you have the extra leveling Northern valves? I've never seen an air flow drawing with the Liberty valves.

Joe Camper
10-10-2017, 05:58 AM
Gill Liberty put 2 more norgrens so they can facilitate opporating all 3 corners manually, simultaneously. They r the only ones who do it without adding HWH leveler.

Rocky, u r absolutely correct. When u key off every 3 position Spool on the chassis should lock out and hold air.

The spool can leak more ways than I care to guess.

Sometimes a leak does not manifest itself right at the valve. If the spool or its oring or its bore is bad it can leak back up a feed line. U will not hear or see it at the valve unless the leak is bad and u have the correct ultrasonic leak detector.

I do a simple test for the left and right rear 3 position, on the bus.

Raise the rears till u can place stands at the support points and then bring down those corners till just before u land the chassis. Leave 1/4, 1/2 in. Stop there leave stands in place. Then go to the norgren. There will be 1 fitting out the top. A T fitting with 3/8 plastic line. That is what is supplying the air bags. If that norgren is holding air completely u should be able to remove all the other lines on that valve. The bottom pair of 3/8 lines and the 2 1/4 in signal lines on both ends and that corner should still hold air.

That's what experiance has taught me to be the easiest and safest way to bench test them, on the bus. If it does leak it will only settle down very gradually to the stand and it won't be much.

Have good stands know where to put them, then add secondary backup whenever extra supports r plentiful.

Joe Camper
10-10-2017, 06:16 AM
John

All that 2 position spool is for under the driver is an exhaust port for level low function, and that's for all 3 corners. If it is bad all 3 corners would do the same thing.

Your problem is the 3 position norgren at the left rear and potentially other components at that corner.

If the bus was correctly supported, and u left air in the left rear suspension. If then the black 1/4 in. signal lines on opposite ends were removed from that left rear 3 position valve, I think what u might find air is escaping and it shouldn't be. Escaping air that is going backwards through a system. When u start pushing air backwards all kind of odd difficult to explain things happen.

GoneCrazy
10-10-2017, 09:11 AM
Rocky,

Can you figure out why you have the extra leveling Northern valves? I've never seen an air flow drawing with the Liberty valves.
I cannot find one that has them either. Liberty added them and they are electrically actuated.

Joe Camper
10-11-2017, 07:13 AM
Rocky those additional 2 valves r so u can adjust all 3 corners simultaneously in level low. Liberty takes away the 4 position selector and replaces that with 3 rocker switches 1 for each corner that can be adjusted at the same time. There is a norgren attached to each of the 3 rockers Liberty puts for manual leveling. It's a quite simple mod once u understand what has been done.

Also only on Liberty, if u look at your norgren control manifold on the back wall of the steering bay prevo used all 24v solonoid but Liberty pulled the 24v control solonoid off the manifold and replaced it with a 12v. U have 4 24v and 1 12v solonoid on the Block.

GoneCrazy
10-11-2017, 09:12 AM
Joe,
I have a classic. So that 5 port stack with the coils and armatures that control the pilot air has four 12 V coils and one 24V coil. The third one down is for ride height and it is 24V. Been into that block a while back. Changing coils and armatures. Classic owners should carry a spare 24V coil. They have the highest fail rate, ( according to all I have read in the archives.) Since they have voltage to them anytime the key is on and the level low is in road height mode. My 24 V will get pretty warm to the touch. The way I understand it the four 12 V coils are only activated in manual mode or auto leveling mode. :confused:

Gil_J
10-11-2017, 09:29 AM
Rocky,

You're right on. The ride height coil is energized the whole time the key is on and yes it will get warm. I've had one fail. Thankfully, I was close to a Prevost facility. Had I not been, I could have moved one of the level low coils. In your case, your level low coils are 12V. So, for Liberty Chassis owners, carrying a spare 24V coil would be a good idea. An even better idea would be to replace the ride height coil and keep the old one as a spare.

Based on what Liberty does with their extra valves, I think they could have done the same with the factory manifold and a few diodes.

503rdPIR
10-21-2017, 10:26 AM
Gil and Joe,

Just an update on my "sinking coach syndrome". Following your competent advice I was able to isolate the problem to the Norgren valve on the right tag. After replacing the valve the problem is solved and all is well. Thank you both for your assistance and for sharing your knowledge and experience.

Don