[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..