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-   -   Leak in air supply (https://www.wanderlodgeownersgroup.com/forums/showthread.php?t=6482)

Dennis 05-25-2010 12:00 AM

Leak in air supply
Here's the symptoms: Front slide would not retract into the Coach. Checked the air pressure in driver's side bay 2 and found very low pressure. Ran the engine for about 15 minutes and the pressure went up to 90 lbs and I was able to close the room. Then noticed the Coach was not raised up on the air bags and brake air pressure both front and rear would not go up past 75lbs. Obviously a leak in the pressure system that is real bad, but by racing the engine I can put more pressure in than is going out, but idle the engine and it goes out fast. I did hear a unusual noise in the bay under the driver where the window washer tank/aux air compressor is located, sort of a bearing noise; the noise seems to be coming from a part called the "pumptrol." When I race the engine 1,700 rpms the curb side of the Coach raises higher after several minutes than the driver side of the Coach by at least 2 inches. My questions: 1. Are there separate air supplys for the Coach air bags and brakes than the supply for the slide out seals? I ask the because I have a front slide out seal leak, but have had this leak for almost 2 years (repaired it once, but it did not last) and the slide and Coach worked fine (aside from the hiss). One possibility is that the air leak in the front slide has become much worse and as such the air is leaking out much faster. But I would be surprised that a seal leak would disable the Coach from being driven because of low brake and air bag pressure.

Question 2. Is the parking break dependent on air pressure - I have parked the Coach on a level and used good wheel cocks, but would like to know if the parking brake can be trusted.

Question 3: If it is not the room seal causing the lack of air pressure for the air brake and air bags does anyone know anything about the function of the "pumptrol?"

Last question 4. If I have to buy a new seal do you know where I can do so and can I trust someone who knows Coaches but has likely never installed such a seal to do the job right? I will likely try to repair the seal once again, but if that doesn't work I will obviously have to buy one. The problem too is that I will not be able to drive the Coach to get a new seal since the Coach will ride up on the air bags in addition to being low on air brake pressure.

Thanks as always,


iamflagman 05-25-2010 05:23 AM


Originally Posted by Dennis (Post 58285)
Question 2. Is the parking break dependent on air pressure - I have parked the Coach on a level and used good wheel cocks, but would like to know if the parking brake can be trusted.
Thanks as always,



I can't help with the slide questions, but if you are talking about using just the Parking Brake to hold your 'Bird where you park it while in your storage space in Malibu, as seen in the background in this picture, as we talked about back when we met up there, I personally would feel much better with using the wheel chocks and a good pair, as a backup to the parking Brake, but that is just the way I feel, not a requirement. If you look at most Fire Departments vehicles whenever they are parked they throw a set of substantial wheel chocks behind or in front of the wheels depending on the grade until they are ready to move again.

Can the Parking Brake be trusted to hold your 'Bird on level ground, Yes as long as everything is working as designed, they should be sufficient to hold it.

The Parking Brake is dependent on air to RELEASE IT, here is a description of the Service and Parking Brakes from;

California Commercial Driver License Handbook.
Section 5: Air Brakes


Spring Brakes
All trucks, truck tractors, and buses using air pressure to apply the service brakes must be equipped with emergency brakes and parking brakes. The parking brake must be held on by mechanical force (because air pressure can eventually leak away). Spring brakes are usually used to meet the emergency and parking brake requirements. When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes. A parking brake control in the cab allows the driver to let the air out of the spring brakes. This lets the springs put on the brakes. A leak in the air brake system will generally cause the springs to put on the brakes.

Tractor and straight truck spring brakes will come fully on when air pressure drops to a range of 20 to 45 p.s.i. (typically 20 to 30 p.s.i.). Do not wait for the brakes to come on automatically. When the low air pressure warning light and buzzer first come on, bring the vehicle to a safe stop right away while you can still control the brakes.
The braking power of spring brakes depends on the brakes being in adjustment. If the brakes are not adjusted, neither the regular brakes nor the emergency/parking brakes will work correctly.

Parking Brake Controls
In newer vehicles with air brakes, set the parking brakes using a diamond shaped, yellow, push-pull control knob. Pull the knob out to set the parking brakes (spring brakes), and push it in to release them. On older vehicles, the parking brakes may be controlled by a lever. Use the parking brakes whenever you park.

Caution. If your vehicle is not equipped with an anti-compound system (only in vehicles with air brakes), you should not push the brake pedal down when the spring brakes are on. If you do, the brakes could be damaged by the combined forces of the springs and the air pressure. Many brake systems are designed so this will not happen. But not all systems are set up that way and those that are may not always work. It is much better to develop the habit of not pushing the brake pedal down when the spring brakes are on.

Robert Britton 05-25-2010 10:34 AM

Dennis, when you bring up the air pressure to 75 lbs. on the brake system, will it hold there for a while or does it leak down as soon as you shut down? If it’s leaking down rapidly you should be able to hear it leaking…maybe a brake pod. Also might want to check purge valve on air dryer is not leaking air?
If the brake system is holding air, then the leak is in the accessory air system but this should not drain down your air brake system. In fact, if you loose all of your air your brakes will be locked up as it takes air to release them.

I don’t think the leak in your slide seal would effect you airing up the coach, what you are describing is a large air leak. So I guess the question is; will the system hold air and can you hear an air leak when you shut down and do a walk around the coach. If the system is holding air but just won’t air up past 75 lbs then it might just be the air governor. On the M380 the governor is located on the right side of the engine as you face it from the rear.

lnchaffin 05-25-2010 11:07 AM

You can cut off all air to the slides by turning the dump valve on the air manifold. This will eliminate the slides leaking but you would be able to hear a leak that big.

Robert Britton 05-25-2010 11:12 AM

2 Attachment(s)
I forgot to address your question on the pumptrol. Looking over that device it looks to be the regulator for the aux air system. There is a small air tank in that compartment that stores air for the slide and probably air to the step cover. When air pressure in that small tank drops; the pumptrol signals the aux air compressor to turn on and bring up pressure in the tank.
The aux air compressor will also maintain pressure in the other coach systems as well. I am not sure how it is plumbed but I know for sure that it does run air through the air dryer before filling any of the other tanks to about 90 lbs. So it does seem to be inter connected.

Not sure if that helps clear anything up but maybe gives you some areas to look at. I attached a couple of pics of the air governor.

Dennis 05-25-2010 12:42 PM

Thank you guys, your help is very much appreciated.

First to John Finn: John right after you commented on my plastic wheel chocks I went out and bought 4 of the very same large rubber wheel chocks that the Fire Department uses; so it is interesting that you mention them in your response. I did assume that the parking break worked independent of the air system for the very reasons you mention otherwise it would not be safe - but I did not want to act on my assumption so thanks for confirming.

Robert: I actually got the right and left air pressure gauges both up to 100 psi while driving on the highway, but they drop when at idle. The Coach actually did rise up as well, but dropped down rapidly at engine idle. It does hold some air pressure just at or below/above where the warning light/buzzer low air pressure comes on/off.

I tend to agree with you that the slide seal leak is not causing this problem in fact this morning it occured to me that perhaps the valve (or what ever it is?) that releases the air from the suspension is stuck since this problem did not occure when I drove to the campground, but only when I was leaving a few days later.

I opened all the bay doors and could not hear any leaking air other than the one from my slide seal that has been leaking for nearly two years. (I do plan on trying to patch that leak again.)

I know where the small air tank is that you speak about. The aux air compressor is usually how I power up the system to close the front slide when at a campground so I do not have to disturb others with running the engine, but in this case the aux air compressor could not produce enough air pressure so I had to high idle the engine as described in my original message above. Also the aux air compressor never came on by its own.

Lloyd: If I cut off the air to the slides would that channel any air supply to the suspension and brakes?

In either case I would like to know where to find that dump valve on the air manifold. Where is the air manifold, what does it look like and where is the valve?

All: What does the air governor look like? Is there a way to know if it is the problem?

Also if the suspension dump value is the problem where do I look and how can I test this?

I was thinking about trying to recycle the dump valve switch after work today to see if this does anything. One of the reason I am thinking about his area of possibility is because the curb side of the Coach is rising about 2 inches more than the driver's side when I high idle the engine for several minutes.

Thanks again for your help and insight.


WTarrier 05-25-2010 12:42 PM

not an expert on the air system, but that much air coming out needs to be from something large. Could one of the suspension dump valves be hanging open? Even that should not impact the brake system at all.
I had a much smaller leak on the non-brake side that I traced (by hearing) to a "chewed" 1/4" line to the holding tank valves. Something had gnawed its way through the line. Brass compression fitting and I was back in business. Even though it seemed to be a large hole in the line, it took a while to bleed down, and airing up the suspension seemed normal.
They are pricey, but several members have the ultrasonic leak detectors. Perhaps you could borrow one to find the leak. I believe Tom Warner has one.

Bill Pape 05-25-2010 01:02 PM

"All: What does the air governor look like? Is there a way to know if it is the problem?"

the govorner looks exactly like the first picture that Robert posted #5, It cycles the compressor pressure 90 to 120 psi.

Dennis 05-25-2010 01:37 PM

Bill Tarrier: Funny that you should mention "chewed" as I did have a rat in the bay over the weekend that this happened. But I did not hear any leak sound and still don't.

Where is the holding tank located? Is that the tank in driver's side bay #2 where the slide control valve and pressure guage is located?

When you say the non-brake side are there different air systems for the brake and the suspension?

Bill Pape: Thanks I totally over looked the photos in reading the text.



The_Money_Pit 05-25-2010 01:58 PM

Hi Dennis,

Looks like it is time to get dirty. I just recently went thru my own set of air leaks, and what worked for me was to crawl under the coach with a spray bottle filled with soapy water. Of course I put some heavy duty jacks under there as well for the peace of mind.

There are just to many places that can leak air. But some of the more common ones are

1. air dryer purge valve
2. PPV valves
3. dump valves

I lifted coach with leveling, and then in addition to the jacks I put heavy duty jack stands under the frame, and chocked the wheels

I then aired up coach using aux air compressor, then shut it off

then crawled under coach with spray bottle filled with soapy water. I didn't have glasses, recommend glasses.

and started spraying anything and everything that made any kind of noise. I got soaking wet, dirty, cramped, scuffed, and upset, but eventually found my 2 air leaks.

other than that, get it to a shop with a pit, and have them find the leaks.

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