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Mystery air leak...U320

Air psi in the lower of the two dash gauges falls faster than the upper gauge while my 1997 U320 sits parked.

I've soaped all 8 airbags, both 6-packs, all brake hoses/fittings at the calipers, the protection valves and related hoses, all 3 wet/dry tanks and their fittings, the 2 gauges under the coach, the Haldex and related fittings, the D2 and the hose coming from Haldex  to the D2as well as the under-front-door step cylinders/Ts and hoses. No leak found yet.

I can hear air hissing from the parking brake for a split second when it is first engaged at a parking site. It stops hissing as soon as the yellow knob is fully engaged in the 'out' position. Same hissing when yeloow knob is disengaged for a moment.

What air components are unique to the lower gauge and not the upper dash air gauge? Perhaps this will give me a clue to the source of the leak.

My hearing is 'selective' so my SuperGirlFriend says. I can't hear or see any leak but the bottom gauge shows a 20 lb. decrease after a few hours while the upper gauge is solid at 115ish for 2 days.
1997 U320 40'  Orlando, FL
"Purple Haze" which will soon be for sale.... !

Re: Mystery air leak...U320

Reply #1 –
I found the Hadley Horn solenoid leaking. It's found attached to the back of the air pressure gauge. On my coach. But I have one gauge, 2 needles. There are also other connections to the horns that can leak.
1994 U280, Build 4490
Deming, NM.

Re: Mystery air leak...U320

Reply #2 –
Quote from: StevenOrlando –
Air psi in the lower of the two dash gauges falls faster than the upper gauge while my 1997 U320 sits parked.

I've soaped all 8 airbags, both 6-packs, all brake hoses/fittings at the calipers, the protection valves and related hoses, all 3 wet/dry tanks and their fittings, the 2 gauges under the coach, the Haldex and related fittings, the D2 and the hose coming from Haldex  to the D2as well as the under-front-door step cylinders/Ts and hoses. No leak found yet.

I can hear air hissing from the parking brake for a split second when it is first engaged at a parking site. It stops hissing as soon as the yellow knob is fully engaged in the 'out' position. Same hissing when yeloow knob is disengaged for a moment.

What air components are unique to the lower gauge and not the upper dash air gauge? Perhaps this will give me a clue to the source of the leak.

My hearing is 'selective' so my SuperGirlFriend says. I can't hear or see any leak but the bottom gauge shows a 20 lb. decrease after a few hours while the upper gauge is solid at 115ish for 2 days.

Protection valves can leak back internal, ask me how I know

Also check the step and slide cover cylinders, both in and out position. Not the fittings, but the cylinders themselves.

Chris
Chris and Tammy White  CDA Idaho
Previous owners 1997 U295 36' 3126 Cat 300 HP Build # 4998
Former Foretravel tech & RVIA certified tech
Former owner Custom Satellite home/RV satellites 
Former owner Vans LTD  van conversions
Unemployed, panhandler, drag racer NHRA #6348

Re: Mystery air leak...U320

Reply #3 –
Sounds like you have an internal leak. You need to check the check valves at the dry tanks inlet for crud.  They can be removed and separated to reveal a spring and disc.  It is just as cheap to replace them than to ty to install a rebuild kit.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Mystery air leak...U320

Reply #4 –
Ditto what others have said.  I had to replace the check valves, pressure protection valves and the door step regulator.  Since then, tanks will hold pressure for weeks.
40ft 1997 U320

Re: Mystery air leak...U320

Reply #5 –
Quote from: StevenOrlando –
What air components are unique to the lower gauge and not the upper dash air gauge? Perhaps this will give me a clue to the source of the leak.
First, don't worry about the parking brake hissing a bit during operation.  It has a exhaust port as part of the valve where pressure is vented when setting and releasing the parking brakes.  When the air brake control leaks it commonly does so around the shaft that moves out and in as you pull/push the knob.  Try to (gently) wiggle the shaft back and forth sideways to see if you hear air leaking.

As to your question (above) the Air System Diagram is your friend.  One dash air gauge reads pressure in the front (brake) tank - the other gauge reads the rear (brake) tank.  Both "front" and "rear" brake tanks are located at the front end of your coach.

So, first you need to know which tank is being monitored by the lower gauge.  It might say something about that in your Owners Manual...or not.  If not, then perhaps a Forum member with the same year coach will tell us.  OR, you can determine it by experimentation.

However you figure it out, once you know which tank is losing pressure, then you look on your air system diagram to find the components served exclusively by that tank.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Surely, no age has been more fraught with insecurity than our own present time."

Re: Mystery air leak...U320

Reply #6 –
FRONT refers to the front air brake system reservoir and REAR refers to the rear brake system reservoir. There is also a "wet tank" that supplies air to both brake reservoirs. On our coach there is also a separate tank for the HWH system components.
As mentioned before you need to look at your air systems diagram to see how all of the plumbing is put together.

Steve
Steve & Sandy
2003 U320 4220 WCDS, build#6160
Motorcade #17794
USMC '67-'71

Re: Mystery air leak...U320

Reply #7 –

 air leaks are a mystery
.
1993 U300, 6v92
build 4366
USAF retired, Flight Engineer, C124, C130
 ATP, A & E.  & ex AI
 

Re: Mystery air leak...U320

Reply #8 –
Soap works well but not always, take a two foot rubber hose or any length that's easy to handle and start searching if you have hearing loss this works well as you have the hose to act like a stethescope.  I have found it works well for me.
Andy & Eileen
MONTROSE COLORADO
1992 U300  40' 6V92 TA
2016 4 Runner
1998 Jeep Grand cherokee

1998 Jeep Grand Cherokee) Build # 4135 Skp# 122921