Leaking air when braking

[Kevin McKeown]

Coming home from the weekend in my BB last night, I was in some heavy
stop and go traffic, and I kept hearing some hissing of air whenever I
applied the brakes, and watched my air pressure begin to go down
noticibly when the brakes were activated. When I let off the brakes,
the hissing stopped, and the air began to build up normally. The air
sounded like it was somewhere street side, toward the middle or front
part of the bus. It was like an air line to a wheel came off, but the
brakes worked fine. The air got down to around 70 PSI, and after about
5 minutes of this 0-10mph using the brakes only when necessary (big gap
to the car ahead of me) everything return to normal...no more hissing
on braking, pressure built up to around 125-130 PSI and purged from the
dryer, etc, and the rest of the 60 or so miles home were uneventful.
Don't we love these intermittent problems....

Something stuck, and now OK? Something to look for/replace? Since it
is OK now, where should I begin to look? I was afraid of getting stuck
on the So Cal Fwy's when the air got down to 30 PSI and my brake button
popped...ideas??

Kevin McKeown
Yorba Linda, CA
1986 38' PT