Air leak on brake

[Cary and Don]

OK, here's the question.

We thought the brake relay valve was leaking, but it isn't.  When applying the brakes air it blowing out the exhaust on the inversion valve.  It doesn''t leak when the park brake knob is pulled. It seems to leak the worst when applying the brakes lightly. Loses about 5lbs a minute if you hold the brake half way down.

Why would this valve that is suppose to do the parking brake leak during braking?  Is it the valve or is there something else wrong that is making the inversion valve blow air?

We are getting ready to go on vacation, brakes would be nice.  Any Ideas?

Don and Cary
GMC4107
Neoplan AN340

[Airbag]

Call these guys they have forgotten more than I will ever know about the subject.

1-800-AIR-BRAKE (1-800-247-2725) hotline.

[Dreamscape]

What is your air loss with a full brake application?

Your valve might not be seating on the exhaust side because of lower air pressure, therefore allowing air to escape.

Just a thought.

Paul

[Cary and Don]

The odd thing is,  there is very little loss if you brake clear to the floor, even if you hold it there.  It seems to be far worse if you are doing an easy braking.

Don and Cary
GMC4107
Neoplan AN340

[TomC]

One of your brake cans has a hole in the diaphragm.  Easy to tell which one-take a vice grip and pinch off one brake hose (the one coming from the relay valve to the brake can) one at a time.  When you find the one that it doesn't leak, that's the one with the bad diaphragm.  What is happening is that the hole in the diaphragm is leaking back through the relay valve making you think that the relay valve is bad.  Good Luck, TomC

[Cary and Don]

The air is leaking back through the inversion valve.  The relay valve seems fine.  The air is blowing out the bottom of that inversion valve though.

Don and Cary
GMC4107
Neoplan AN340

[wildbob24]

What TomC said, except the leaky diaphragm is one of the parking diaphragms not the service diaphragms(each DD3 has 2 diaphragms).

His diagnostic procedure still still work, just clamp the hose between each chamber and the inversion valve to determine the culprit.

[Jriddle]

Don
I am having a similar problem but the inversion valve will start leaking when park brake is released with no service brake application. I have ordered a new rebuilt invertion valve. Keep me posted on what you find.

John

[Cary and Don]

We are currently checking the parking brake diaphragms.  We are so hoping it is that and not the inversion valve.

Don and Cary
GMC4107
Neoplan AN340

[Jriddle]

Don

Not sure about these guys but placed on-line order I will let you know if I get stiffed.

http://www.anythingtruck.com/Merchant2/merchant.mv?Category_Code=HTP-AIRB&Product_Code=061-277340X&Screen=PROD

John

[Dreamscape]

John,

I have purchased a couple of things from them in the past, good to deal with was my experience.

Paul

[Jriddle]

Thanks Paul

John

[NJT 5573]

The TR 3 Inversion valve 101450, Bus, with common control and supply pressure, the inlet opens at 25 PSI descending pressure and exhaust opens at 40 PSI ascending pressure. Maybe it is just doing its job, if you don't find a diaphram with a hole in it.

Sometimes air valves stick and need to be exercised by putting some air through them. I like to pump my air systems all the way down with the treddle every once in a while just to keep them working.

[Cary and Don]

Victory!!!

One of the parking diaphragms had a big hole.

For anyone that has vague problem here is what was happening.

The inversion valve blew air when the brakes were applied.  It seeped air if none of the brakes were on.
The Relay valve blew air when the parking brake was set, with or without application of the brake pedal.

It was soooo much easier to change that diaphragm than those valves, and we even had a spare diaphragm here that fit! 

The only minor thing we haven't figured out now, is the push pull valve has a small leak when the brakes are applied with the brake pedal.  Any Ideas on this?  We changed out one and the replacement does the same thing.

Thanks for all the help,  we would never have thought "parking brake diaphragm".

Luck Day!!

Don and Cary
GMC4107
Neoplan AN340

[Jriddle]

I replaced the inversion valve today and fixed most of my air leak problems. It now takes at least two hours to go from 118 psi to 90 psi. I have removed all of my automatic leveling valves and have installed manual valves there. I am glad to here you problem is solved and now mine is as well.

John