07 VT830 gushing air from front passenger side brake chamber service brake applied

The brake chamber is the problem.

 

diaphragm inside the brake chamber has a hole in it

 

I am inclined to think the diaphragm is got a hole in it.

Not only you should be losing air with a hole like that your primary should be falling pretty good followed by secondary. Only when your service brake is applied.

One of the things that I had when it made a hole in mine that time was too much stuff inside the air system on mine. No air dryer or cleaner. Just drain every night. And so it got to the diaphagm and ate a hole through it. Once replaced and air system is drained every night it improved. But ultimately a installation of a air dryer would do much better on that older truck.

 

You'll be out of service if you don't.

Brake chambers are cheap. Buy it over the counter at a dealer or at a parts house, then get a TA or some other shop to do the labor if you'r not into it yourself. I'd replace that one and the corresponding one on the other side at the same time.

 

Not necessarily. There is a diaphragm inside of it that can start to leak around the edge or may develop a small crack or hole. If you're feeling air only when you step on the brakes then that's what's happening.

Here's a video that shows a guy replacing just the diaphragm. I'd do the whole chamber myself, but this is instructive.

brake can repair type 30/30 service break air leak

 

It’s the diaphragm, bought 2 brake chambers today, 40 bucks each. You con change the rubber diaphragm if you can find one,just one bolt to change it.

 

Steer axle? If air is leaking from the service chamber itself, the diaphragm is blown. Plain and simple.

And no, there will always be air passing through the ABS modulator valve during a service brake application. It will only come out of the modulator's exhaust port during an ABS event.