[Jrahn56]

My original problem was coach #375 was not building air pressure, running on fast idle for 40 minutes it would only build up to 75 psi on the brake gauge and 75 psi on the supply. Most everyone said it was the air governor. After a monumental task of getting the old governor off, which had to be cut off in pieces, I managed to relocate the new air governor to the fire wall in the right rear engine compartment. When I started the coach up, fast idle for 40 minutes and the air pressure built up to 75 psi in both brake and supply. When I shut the coach off, I watched the supply gauge drop to 0 psi, within a minute, the brake supply gauge is holding at 73 psi. I didn't hear any air leakingor sissing, and I have sprayed every fitting I could find with soapy water and no leaks. During my investigation my brake supply tank was about 1/3 full of water. I drained that and installed a new remote drain valve. I also found a tank welded into the cross member in the rear and drained that one. I found the air tank in the right tag axle wheel well and drained that one as well. Does anyone know what I should check now? The guys at Newell weren't any help.

Thanks,

Jeff
Coach #375

[cwl1979]

Have you checked your pressure protection valve? If your close to a truck shop of any kind you can get a new one and replace it. They are not expensive. That would possible explain why you cant get over 75PSI on your gauges. Do the airbags inflate?

[Richard]

Hmmmmmm, that is a big leak.

Check the bottom of the R 12 brake relay valve located above the drive axle.

Can you provide shop air to the fitting in the engine compartment. If you can you should be able to hear a leak that big.

[Jrahn56]

Have you checked your pressure protection valve? If your close to a truck shop of any kind you can get a new one and replace it. They are not expensive. That would possible explain why you cant get over 75PSI on your gauges. Do the airbags inflate?

---

Thank you, I will need to locate that pressure control valve and replace it.

Thanks again,
Jeff

[johnkosir]

When you say the supply side drops to 0 and the brake side stays at 73, I would guess that your bigger leak is on the supply side side. If I couldn't hear the leak, I would start breaking the system down into smaller parts to find out what is leaking, On 712 my house system gets air from the dryer I have a ball valve in that line I can turn it off and split the system into 2 parts I have ball valves on every line leaving my tanks so I can shut them off

[Richard]

Jeff,

I think you have been chasing this air leak since the late summer. Take what I say with a boulder of salt, because my commentary is solely based on the info you have reported. I am not a fan of randomly replacing parts because some else once had a problem in that area. My comments are going to be directed at diagnostics.

First, you MUST connect to an external air compressor and use as long of hose as possible. You want the noise of the compressor to be as far away from the coach as possible. It is impossible to find a leak with the engine running. Also an external compressor may allow you to raise the coach on the air bags making access easier. If you do go under PLEASE support the coach with cribbing or jack stands.

First thing I would do is hook up the external compressor, open all the bay doors, and have a listen. Something with an inside tour. There are a number of listening devices that may help. I have an Infinicon. Gadget Guy has something fancier. They work best when used with ear buds.

Assuming you don’t find anything. Disconnect the external air for the next test.

I am working off, that you build 75 psi max on the brake tanks, and 75 on the supply side. When you turn the engine off, the brakes stay at 75, and the supply(house) drops quickly to zero? Is that accurate?

The reason the brakes stay at 75 is that there are check valves on each tank that prevent air from going backwards to the supply side. Makes senses from a safety standpoint.

If there is a large leak in the brake system, the PPV would behave just as it should and cause that. However, a massive leak in the supply side would also explain this, since the PPV is designed to divert all air to the brake side UNTIL 60 psi or slightly more is reached on the brake side. Since the brakes stay up at 75, I doubt the leak is in the brake system. I also think the PPV is doing exactly as it should.

Run this test next. Pump the brakes until the brake side is below 20 psi. Crank the engine. How long does it take to build air up to the 75 psi mark. If two minutes or less, then the leak is likely on the supply side of the coach, if five minutes or more, then the first focus should be on the brake system. That may sound a little contradictory to my first conclusions. The purpose of this test is to confirm what we already think we know.

Please do the two things above and report the results. We can go from there on diagnostics.

Also when you look at your airline connections are they still push to connect or converted to compression? The reason I ask, is the next step is going to be to disconnect systems one by one, and install a dead end on the disconnected line. You need to make or have a few dead ends to match what you disconnect..

[Jrahn56]

Richard, yes I have been chasing this leak since late summer (August), but I travel for work and haven't had as much time as I would like to devote to the coach. I have 75psi on both supply and brake, but I have an external air compressor that I will hook up to the air coupler in my engine compartment. I wasn't sure if that coupler had an inline check valve that would prevent back charging that air line. I also have a 30' air hose to isolate the compressor. Then I will listen with all the bay doors open and go under the coach as well. The coach is currently sitting on 4-22 ton jack stands for safety. I  will then conduct the tests and report back.

Thank you,
Jeff

[johnkosir]

I agree with everything Richard said. I installed  1/4" pipe ball valves to isolate parts, the logic being that in the future when you are looking for leaks and it is when not if you can isolate parts very easily. I would have more air hose with a ball valve beside me so I could wait for the compressor to shut off then open the valve and listen for leaks, I built a bubbler to show me how much air is going down a line instantly. I read a post by I believe Newell 77 that said it is more important to know what is not leaking so you don't waist time looking for a leak that does not exist

[Jrahn56]

First thank you for your reply, when you say you built a bubbler, what is that? My PPV and check valve arrive tomorrow so I am anxious to see if that does the trick. I am still going to try to pump up with my external compressor and look for leaks again.

[Richard]

If it were me, I would do the leak tests with the compressor before the arduous and difficult task of changing the PPV.

That said, if your compressor input holds at 120 and you still don't build air over 75, that would be a smoking gun on the PPV. That's a big IF.