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Old 08-09-2016, 10:14 PM   #1
Mini-Skoolie
 
Join Date: Aug 2016
Location: Battle Creek, MI
Posts: 28
Year: 1997
Coachwork: Blue Bird
Engine: 5.9 Diesel Cummins
Low Air

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?

Sorry if this is in the wrong sub forum
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Old 08-09-2016, 11:45 PM   #2
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Join Date: Jul 2015
Location: Montana/Texas
Posts: 175
Year: 1998
Coachwork: Crown by Carpenter
Chassis: International 3800
Engine: DT 466e
Rated Cap: 16
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...
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Old 08-10-2016, 12:05 AM   #3
Skoolie
 
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Join Date: Feb 2007
Location: Tullahoma, Tennessee
Posts: 198
Year: 2002
Coachwork: International
Chassis: RE300
Engine: DT466E (250h.p.)
Rated Cap: 81
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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Old 08-10-2016, 12:09 AM   #4
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Location: Oklahoma aka "God's blind spot"
Posts: 1,949
Year: 1989
Coachwork: 1853FC International/Navistar
Chassis: 35' Retired Air Force Ambulance
Engine: DT466, MT643
Rated Cap: 6 souls and a driver
I consider it normal on mine
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Old 08-10-2016, 04:08 AM   #5
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Join Date: May 2016
Location: Georgia
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Year: 1987
Coachwork: Carpenter
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Engine: IH 9 Liter
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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).
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Old 08-10-2016, 07:09 AM   #6
Mini-Skoolie
 
Join Date: Aug 2016
Location: Battle Creek, MI
Posts: 28
Year: 1997
Coachwork: Blue Bird
Engine: 5.9 Diesel Cummins
Awesome!! Great info!! Thank you for setting my mind at ease ����
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Old 08-10-2016, 08:34 AM   #7
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
Posts: 3,403
Year: 1991
Coachwork: Carpenter
Chassis: International S3800
Engine: DT360
Rated Cap: 7 Row Handicap
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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Old 08-10-2016, 08:44 AM   #8
Mini-Skoolie
 
Join Date: Aug 2016
Location: Battle Creek, MI
Posts: 28
Year: 1997
Coachwork: Blue Bird
Engine: 5.9 Diesel Cummins
HA! It DOES, and that makes TOTAL sense.
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