[Billy]

Your vintage coach can and will drop or lean regardless of whether your aux pressure is 0 or 120.

When the key is off on your vintage coach the Norgren valves that are responsible for directing the flow of air to or from the air bags go to a position in which they lock whatever pressure is in the air bags in them.

So you dropping in the front of the coach is going to be associated with leaky front air bags, a leaky fitting at the air bags or Norgren valves or the Norgren valve(s) themselves. I can’t remember if you have one 5 port Norgren or two 3 port Norgren valves to control your front air bags, but start there and then check all fittings and the air bags themselves. Soapy water is a good place to start.

Norgren valves can leak in several ways, either through the valve itself, or sideways out the end caps. Either way they will cause the loss of pressure in the air bags.

Here is free advice worth every cent you paid for it: If you think or know your Norgrens and air bags and push in air fittings are original, don’t waste your time or spend money to get someone else to look for leaks. Replace the valves, air bags and fittings.

You also need to understand if your coach auxiliary air system is isolated from the Prevost accessory system because understanding your coach and its systems help with managing the coach and identifying potential problems. I’ll let Marathon owners add to the discussion if they want.

[Alex]

Ales,

Unless you have the yellow valve in the steering compartment open, your Compressor is only supplying air to the Marathon side. As Jon pointed out, even if you have zero Prevost aux air, your Norgrens are locked with the key off. So your front leak is bags, Norgrens, lines, fittings or the front position on the 5 port manifold in the steering bay.

[David]

Yellow valve Truk refers to…..under drivers seat.

[David]

The aux I was referring to is the prevo side, not the house side. The drop shown in the picture is about a day. The air bags are new and the fittings are compression. I soaped the fittings and no air escaping. I also have a ultrasonic tester and do not get any reading of leakage. Either I have a valve sticking or it is an internal valve leak. I will need to block up the bus to feel safe enough to get under to check further.

thanks

Alex

[Liam]

2 separate issues.

Lets start with the AUX air gauge on the dash. on our coach, which is an XLII and not an “H”, with the key off, that gauge is connected to the 2 separate 4-6 port plastic manifolds in the back of the steering compartment and is connected to 8-10 different things.

1. The line to the gauge on the dash.

2. The drivers air seat.

3. The supply line for the tag lift toggle switch.

4. The air line to the tilt-telescopic foot switch.

5. The supply line that goes all the way back to the belt tensioners.

6 It is the air supply for for one of the Norgrens just below them and the 5 port “thing” that has the 5 electric solenoids just below it them.

If any one of these systems has a leak, with the key off, the gauge will drop.

Whew…Don’t take my word for it. The Prevost Car website has the pneumatic diagrams that you can refer to. Here is a link “Technical Publications” area that has the pneumatic diagrams.

We have spent more than a few hours in that area running down air leaks.

The Front Suspension leak(s). Here is just another little thing that you can do to help find the leaks. With the engine running raise the front end as high as it will go, turn the key off without returning the level low selector to “Drive” height. Then spray as much of the front suspension, air lines and Norgrens with your favorite bubble solution as possible. Raising the front end will add just a few P.S.I. to the front suspension system and might make the leak(s) a little easier to spot.

Be safe.

[Archived]

So your yellow valve is open correct, that’s the only way you get aux air to the Prevost side?

[AL]

Thanks Tim, I try that this weekend.

Tom, no I always keep that closed. When I said aux, I meant bus accessories air. Then Marathon side has its own set of leaks that I am chasing.

Thanks

Alex

[Archived]

So you have a second aux air compressor the only supplies air to the Prevost side?

[Dick]

Pictured are two (2) manifolds installed on Marathons and known trouble makers.

[Archived]

Tom,

I have a aux compressor that supplies the Marathon side and the main compressor off the Diesel supplying the three tanks (A,F,R) on the Prevost side.

Alex

[Archived]

Al,

I soaped down every connection in that compartment and also checked with ultrasonic tester. I have a Bacharach true point 1100 leak detector that has a touch point option to check for internal valve leakage as well, and I get no signs of leakage.

I am hunting down the common point for both front airbags as the whole nose drops equally. Regardless if I shut the bus off with the level low in the drive position or in any of the manual positions, I get the same result. Rear holds fine front drops 2 inches overnight.

In viewing the schematic, my next thought is to go under the bus to check the P/S valve on the acc tank, front ride height valve, and the two 3 way, 2 position Norgren valves.

My luck I am probably chasing more than one leak source.

thanks

Alex

[Archived]

Alex,

Was lost a little when you reviewing your needs. With your intent to go under the bus now ..back on track.

I’am going to put my money on front ride valve. When they get weak and show leakage slowly and increase like yours to overnight.

Next would be tank valves leaking due to age or not closed properly.

AL

[Jim]

I’m nor saying what Al is saying is wrong because they can leak, but with the key off the air should be locked in the front air bags system which takes the ride height valve out of the equation.

If the air bags are leak free, the fittings are leak free, all the way to the Norgren(s) then it is the Norgren valve(s). Yours is an IFS coach so to lock in the air you may have a 5 port or 2 3 port Norgens to perfrom that function.

If they are leaking internally they can either be leaking out the end caps, or leaking through to the three port Norgren in the steer compartment that exhaists air. Locate it by hearing the air escape as you lower the nose, Plug the open port and see if the front goes down. That’s an easy next step. If the front remains up it is the Norgren(s) that are supposed to lock the air in the air bags.

[AL]

Jon…when we were at Jeff’s earlier this summer didn’t we find out that my ride height valve had air all the time and was leaking at a fitting even though it was shut off?

[Archived]

Jon,

If this ride height valve is locked …does that mean air is forced to remain positive pressure at this valve ? Well sort of.

If Alex’s bus drops overnight 2 inches …isn’t that valve still working but defective. It’s a slow leak and rarely would a ride height valve fail 100 % overnight..just saying.

In my own experience two cases of overnight drop were traced to ride height valves leaking.

In another case front drop was a defective tank valve in front suspension system. That drop was so small taking over a week before seeing a noticeable drop.

AL