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Topic: Air Brake Low Pressure Warning (Read 2943 times) previous topic - next topic

Air Brake Low Pressure Warning

Now that I have the coach back AND a day off (those two haven't happened together in the last few months!), I am outside trying to get as much done to the coach as I can.  Anyway, now that I found out I have to get a class B (Texas) license, I thought I would run over the low air pressure sequence which is required but the DOT.  Long story short at 60 lbs., no light no buzzer but the emergency brake did pop out as it is supposed to.  Question: DOT is looking for an audible alarm, OR warning light OR both.  Am I wrong,  I thought the coach did have some kind of warning system other than just the brake coming on?
I called and spoke to Keith at MOT and he said all the coaches are different and to let the pressure drop to a lower level (below 60lbs) at which point a light or buzzer may come on....but I'm thinking that would not do my ANY good if the brake has kicked in at 60 lbs and I'm in the left lane.....Anyone know about what is SUPPOSED to happen?
Thanks,
dave
Dave
2002 295 36'
Build 6006
Motorcade Member 17931
Toad 2003 Jeep Wrangler
2008 BMW R1200 GSA

Re: Air Brake Low Pressure Warning

Reply #1 –
You need to hear from a fellow 2002 model owner for the exact answer, but yes you are correct - you should get a low air pressure warning before your emergency brake pops out.  How far before, what kind of warning, and at exactly what (indicated) pressure, might be variable.  Have you looked in your Owner's Manual, to see what it says?  There should be a diagram and/or description of the warning lights on your instrument panel - do they include a Air Pressure light?  If so, and if you are not seeing it, then further trouble-shooting will be required.

The warning (whatever it is), will be triggered by a pressure switch (or two switches) located somewhere in your air brake system.  Your air system diagram should note the switch location.  If the switch is bad, or one of the connecting wires is loose or broken, then you will not get a warning.

This definitely needs to be corrected before you go for your driving test.
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
"Nature abhors a vacuum"

Re: Air Brake Low Pressure Warning

Reply #2 –
According to the Federal regs,  a light and a secondary warning device(ie: buzzer or other such as a wigwag) are supposed to "alarm" prior to the air supply button/control lever sets the brakes @approximately 60 lbs..
'02 40' U320t  4010WTFS Build 6036 1 slide
Motorcade # 17841
SKP 151920
Retired truck driver
 5 million miler
Still have itchy feet for travel

Re: Air Brake Low Pressure Warning

Reply #3 –
After my post I went back and tried again.  With the engine running, I let pressure get to 120 lbs., begin pumping brakes, at right around 90 lbs. the "level system" light comes on along with a chime.  At 40lbs the emergency brake activates.  I will as you suggest look in the manual for what is specific to my model year. Thx.
dave
Dave
2002 295 36'
Build 6006
Motorcade Member 17931
Toad 2003 Jeep Wrangler
2008 BMW R1200 GSA

Re: Air Brake Low Pressure Warning

Reply #4 –
Quote from: dke1955 –
After my post I went back and tried again.  With the engine running, I let pressure get to 120 lbs., begin pumping brakes, at right around 90 lbs. the "level system" light comes on along with a chime.  At 40lbs the emergency brake activates.  I will as you suggest look in the manual for what is specific to my model year. Thx.
dave
Sounds like you need to replace the protection valve(s) as the regs say 60 lbs not 40.
'02 40' U320t  4010WTFS Build 6036 1 slide
Motorcade # 17841
SKP 151920
Retired truck driver
 5 million miler
Still have itchy feet for travel

Re: Air Brake Low Pressure Warning

Reply #5 –
I get a light and chime (which drive my Jack Russell nuts) at 70 psi and 60 psi emergency brake activates.
John
John and Stacey Smith
Motorcade NO: 11973
1997 U295 CSGI 40'..Build No. 5036     
920 Watts on the roof..CAT Power w/fuel Inj. Programmer
2021 GMC Sierra AT4 1500
EX..2015 Jeep Wrangler Sahara
Ex 1990 U280 RSAI 36'..Build No. 3638

Re: Air Brake Low Pressure Warning

Reply #6 –
Quote from: dke1955 –
...at right around 90 lbs. the "level system" light comes on along with a chime.  At 40lbs the emergency brake activates.
You are seeing the "Level System" low pressure light.  It should come on around 80-90 psi.  The switch that activates that light is mounted on the rear six-pack manifold.  (See HWH page linked below)

"Pressure switches used to monitor system air pressure are usually set at 85 psi, although some manifolds have a pressure switch set at 100 psi."

The "Air Pressure" warning is a different deal - it should come on (like John says) just slightly above 60 psi.  These are two different warning signals, monitoring two different systems, activated by two different pressure switches.
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
"Nature abhors a vacuum"

Re: Air Brake Low Pressure Warning

Reply #7 –
For the brakes the low air pressure alarm should sound at about 60 psi and the park brake should activate around 45 psi .
On my couch (2003 U320) the alarm is the annunciator and is plumbed through the mysterious blue box. No warning light.

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

Re: Air Brake Low Pressure Warning

Reply #8 –
Quote from: John  and Stacey –
I get a light and chime (which drive my Jack Russell nuts) at 70 psi and 60 psi emergency brake activates.
As SteveB suggests (above), I think your emergency brake is coming on "early".  It is more common for this to happen at about 30-40 psi.  In the event of a massive air leak downstream of your "front" and "rear" air tanks, your protection valves should hold pressure in your brake tanks at about 60 psi.  At that point, you still have sufficient pressure to operate your service brakes, and the emergency brake should not activate.

If the pressure in one or both tanks continues to drop, then around 30-40 psi the emergency brake knob should pop out.  The exact pressure at which this occurs depends on the "spring" installed in the Bendix PP valve.  These springs are available in 20, 30, 40 and 60 psi ratings, so it is possible that your emergency brake control has a 60 psi spring.  See manual linked below:

BENDIX PP-1-2-5-8-RD-3 PUSH-PULL VALVES MANUAL Pdf Download.
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
"Nature abhors a vacuum"

Re: Air Brake Low Pressure Warning

Reply #9 –
Seemed high to me also, so I just went out and checked....1) Get alarm at 65psi, Push/pull pops out at 40psi,  Brakes will not release nor will chime and light quit until 70psi.  Thats the way mine is set-up.....Sorry for inaccurate info earlier.

John
John and Stacey Smith
Motorcade NO: 11973
1997 U295 CSGI 40'..Build No. 5036     
920 Watts on the roof..CAT Power w/fuel Inj. Programmer
2021 GMC Sierra AT4 1500
EX..2015 Jeep Wrangler Sahara
Ex 1990 U280 RSAI 36'..Build No. 3638

Re: Air Brake Low Pressure Warning

Reply #10 –
Quote from: SteveB –
For the brakes the low air pressure alarm should sound at about 60 psi...

On my couch (2003 U320) the alarm is the annunciator and is plumbed through the mysterious blue box. No warning light.
In that case, your annunciator would already be sounding due to the LEVEL SYSTEM alarm being activated at approx. 85 psi, and having the AIR PRESS alarm set at 60 psi would be superfluous.  Unless, of course, there are two separate distinctive alarm sounds?

Or, perhaps on the newer coaches, the LEVEL SYSTEM light does not trigger the annunciator?  On our '93, if any warning light along the top of the panel comes on, the annunciator screams.  Plus, of course, other times also, like turn signals, etc.
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
"Nature abhors a vacuum"

Re: Air Brake Low Pressure Warning

Reply #11 –
Seems like everything is coming on at the wrong pressure?
Think I would check to see if the pressure gage is correct before I started chasing other things.
John Duld
1995 U320C SE 40'

Re: Air Brake Low Pressure Warning

Reply #12 –
Yes it is confusing. Are there any 2002 owners out there
Quote from: John Duld –
Seems like everything is coming on at the wrong pressure?
Think I would check to see if the pressure gage is correct before I started chasing other things.
Yes confusing for sure. Are there any 2002 owners out there who are familiar with how our year coach behaves in this situation?
Dave
2002 295 36'
Build 6006
Motorcade Member 17931
Toad 2003 Jeep Wrangler
2008 BMW R1200 GSA