it is the anti compouning valve blowing air ??  when the spring brake is left pushing (park brake on) and someone pushes on the service brakes, the valve proportions the  pressure working the cams on the axle that hold the spring brakes so there is not too much pressure on the shoes. if the valve is crapped out you get broken shoes with no sign of heat that made the cracks .



to keep from giving a lecture  then getting a lecture from the mods,  check out page 27  of  Bendix handbook 



http://www.wsafc.org/WSFMA/Shared%20Documents1/Bendix%20Air%20Brake%20Handbook.pdf

here is a good video of the principles  of AB  without much of the new safety crap confusing the process it is from 1967


http://www.youtube.com/watch?v=qJa5-_ExsBE

Greg
94ptca

--- In "WanderlodgeForum@yahoogroups.com", Curt Sprenger wrote:

>
> Paul,
>
> What you found and determined does not seem right. Post pictures if you can.
> I looked under our coach this afternoon. I see a 1/8" plastic air line to
> the cylinder that rotates down the driving light. Above that area on the

> bottom of the frame rail there are some copper and plastic air lines. None
> are open as you describe.
>
> Curt Sprenger
> 1987 PT38 8V92 "MacAttack Racing"
> Anaheim Hills, CA

>
>
>

> On Sat, Oct 31, 2009 at 2:35 PM, P & D audvid1@... wrote:
>
> >
> >
> > Thanks you all for the assistance. Got some help today and we climbed

> > under coach and found a ¼ air line on the driver side front right behind the

> > fog lights that when you step on the brakes air comes out of that line and
> > as soon as let off it stops. After looking at drawings and trying to figure

> > out where the other end should be connected, by accident we discovered that
> > if you plug the hose, the coach emergency brake released. (Good thing we
> > are on a level lot) and if you un plug it, the emergency brakes stay

> > locked. Then we tried it with the emergency brake released and no air came
> > out, so I think it is releasing the air bypassing the emergency brake so as
> > to not release the emergency brake.

> >
> >
> >
> > Hope all that made sense, but it appears that is normal operation, although
> > I never recall hearing that noise before when I stepped on the brake.
> >

> >
> >
> > Thanks again for all the help
> >
> >
> >
> > Paul & Debbie Potter
> >
> > Hesperia CA
> >
> > 1987 PT 38

> >
> > Hotel California II
> >
> >
> >
> > *From:* "WanderlodgeForum@yahoogroups.com" [mailto:
> > "WanderlodgeForum@yahoogroups.com"] *On Behalf Of *Wayne Kotila

> > *Sent:* Monday, October 26, 2009 1:56 PM
> > *To:* "WanderlodgeForum@yahoogroups.com"
> > *Subject:* Re: [WanderlodgeForum] Air leaking from front when brakes

> > applied
> >
> >
> >
> >
> >
> > Did you check the rubber hoses to the front brakes? When you step on the
> > brake pedal air pressure applies your front brakes so you will have air

> > pressure in the supply hoses to until you take your foot off the brake
> > pedal. Sometimes from age those hoses will start leaking where the end is
> > crimped on the hose and if you need to replace them, a farm supply store

> > will carry high pressure hydraulic hose in different diameters and lengths
> > and have different end adapters to convert the end connector to what you
> > need. You should be able to get a new hose and adapters if needed for under

> > $20.00.
> >
> > Wayne
> >
> > 1996 WB42
> >
> >
> > ------------------------------
> >

> > *From:* ppotter14950 audvid1@...

> > *To:* "WanderlodgeForum@yahoogroups.com"

> > *Sent:* Sun, October 25, 2009 9:38:25 PM
> > *Subject:* [WanderlodgeForum] Air leaking from front when brakes applied

> >
> >
> >
> > Hi there
> >
> > Today while finishing up Air Force One supplemental braking install for
> > towed vehicle, had engine off and when applied brakes to test Air Force One

> > and while pedal was depressed there was a constant air leak up front around
> > the left front area, but could not find it. Any suggestions on where it
> > might be, will work on taking front driver side panel open and looking in

> > there, but it is so tight in there and i dont know what i am looking for so
> > any suggestions would be appreciated.
> >
> > Thanks
> >
> > Paul & Debbie Potter

> > 87PT40 - Hotel California II
> > Hesperia CA
> >
> >
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> >
> >
>