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Why is air leaking out of this valve?

I have a Freightliner Columbia and anytime you press the brake pedal air leaks from the parking/service valve (Red and Yellow Knob Valve). I have looked at every lines, brake chamber and other places outside the truck because I thought it may have been leaking and the sound was just air rushing through the valve. No leaks outside anyplace. It does not matter if you press both knobs in, leave both out or any other orientation of the knobs. The outcome is the same. What can cause this and how do I tell which component is the culprit?

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5 Answers

I think you have air can that's leaking I am assuming it does this when your disconnected from the trailer so that would narrow it to the tractor

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I had a valve doing this, did you check your brake valve on the firewall? Get a spray bottle with some soapy water and spray on all your lines right there on the firewall underneath the coolant reservoir.

If you have a trolly valve, throw something heavy or use a bungee to hold it down with full pressure, that'll supply pressure to the lines to help find it easier, especially while crawling under the truck (should go without saying but CHOCK THE WHEELS FIRST.)

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The air is leaking from the air button manifold (the valve that has the yellow and red knob to set/release your parking brake). But it only leaks when you apply brake pressure. It is not leaking anyplace else. I am assuming that my tractor protection valve on the back of the cab is bypassing air back into this valve when I apply my brake but I have always heard there are several components that can cause this issue and I have no idea how to tell which one it really is.

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have the peddle vale checked.... asap.

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Air leaking from behind the steering colum and seams to be from the #6 port has electric wire or wires coming from the top

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Gary Lynch will be eternally grateful.
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