My bus (1997 Blue Bird/ 5.6 Cummins) is parked on a slight incline while I work on it. The parking brake works (I hear it) and it stays in place. However, when I start it up after a few days it will flash LOW AIR... beep, until the pressure builds up... and then everything is good.
Is that normal? Is that because i'm on an incline? Is that because I have a leak in my brake line?
From what I have been told, this is normal. Most air systems won't stay pressurized for more than a day or 2... My bus will keep pressure for about 36-48 hours... my mechanic said that was totally normal...
Completely normal. Many buses leak down overnight below 60psi. Some leak down in just an hour or two. Some leak down in a week. Sounds like yours is good. There's almost always a slight leak somewhere!
Now if you're hearing hissing under the bus while it's parked with the engine off that's a fairly major leak. That's something to identify and fix. If you're hearing hissing and you lose pressure (under 60psi) in less than an hour definitely look into it!
Remember, when you lose pressure the brakes engage and the bus won't move. Has nothing to do with being on an incline. So if you're worried about it rolling down the hill, don't!
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Daddy, can we go on a trip again??
'85 Thomas SafTLiner RE
3208 NA CAT MT643
I once drove for a farmer who had an International box truck (forget what year, but it had an older mechanical DT466 in it and a 10 speed trans) ... it would hold air pressure for over a month.
But yes, it is rather common for air systems to leak down. The Volvo I recently turned in had 773xxx miles and would leak down overnight. Nothing a couple minutes of warm-up idle time wouldn't fix.
The parking brakes on air brake systems are spring loaded, the "release" is air pressure compressing the spring to release the brakes. There's a rather large and very strong spring in each of the brake canisters, it easily has enough strength to hold it still on a pretty steep hill, and by design, it will stay that way until there's enough air to compress the springs again (typically about 60 PSI or so).
if your bus has an air ride suspension and you walk around in it or work inside it.. ther air suspension will keep trying to adjust for the movement anbd discharge your air-tanks much quicker..
-Christopher
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