Do your bags bleed off?

[Patrick]

My rig settles a couple inches in a day if not started. The guage still says over 100psi. Is this normal? Another air question. Last night I took my rig home for the first time and getting it around an island and some trees requires considerable jockeying. After pumping the brakes while backing...going forward and reverese several times the low air alarm came on. I think it comes on at 100 psi. It took about thirty seconds for the system to recover. Is this normal? I think my running pressure is around 130 psi.

[Doug]

They will bleed off some small amount when the truck sits. Mine would do that when I drove OTR. The shifting of a trialer in the wind, the poressure of the weight on the bags, the slow drain from the exit valves, etc, will usually run the air down. You should drain the tanks every couple of days using the water drains anyway, even if you have an air dryer, to keep moisture from accumulating in the system. It will really screw it up, and repairs are a major pain and expense.
You may have a slow leak too, as I don't think brake use of that type when the truck is running should cause the low pressure warning to come on.

[geof]

In my own experience-you got to pump the brakes many-many times to get the buzzer to come on....maybe 25 times at idle...not impossible-but it is rare....check for air leaks with squirt bottle of soapy water....chock them tires first....no need for that much excitement...geof-near Cincinnati

[Patrick]

I have to back up down a hill and around an island dodging trees so I probably pumped them 20 times. Another factor might be the fact that I have ABS. I'm not sure if ABS systems use more air or not but I do have two dump valves on the dash. About 30 minutes after I parked the rig I heard the air system fart...almost (but a softer sound) like when you depress the brakes. Is that normal as well?

[geof]

ABS doesn't have anything to do with slow speed....I'D still be looking for air leaks...my old army deuce started leaking one nite-sprayed the then copper lines and one was leaking in 10 spots. with the new plastiic lines that is not going to happen, but they do crack/wear around the fittings because of vibration Pop offs are some what startling till you get used to them...Kinda like they got a mind of their own....checking air lines will be a project that will take an hour....geof-Near Cincinnati

[Patrick]

I spoke with a friend who is a trucker and used to be an instructor. He said weekly bleeding of the tanks is important even with a dryer. He said the bag bleed off is normal. The proper way to test the low air alarm is to chock the tires, turn the engine off and pump the brakes until the alarm sounds. It should go off at 60 psi. The gauge that shows applied pressure should never read over 25 psi or you have hot brakes. This is fun learning all this new stuff!!

[Patrick]

Also I heard the fart is normal too. It is just the bags leveling. I was on a slight sideways incline.

[Warpath]

I loose my air in about 8 hours. Which is fine with me, because compressed air left in the system for long periods will cause condensation anyway. I dump the air (I have front & back air bags) before I set the hydraulic levelers as well. My low air goes off at 60 psi and I have never even come close to that. Your low air buzzer setting seems to be kinda high at 100 psi, I would think you could hit that at certain situations as you found.

Bill

2003 28' Show Hauler Motorhome on a 1995 FL 120 www.showhauler.com

[geof]

When i drove for Amerigo If my truck bled off over nite-it went to the shop the next day....my truck had to hold pressure except when I'd blow it down-overnite....company safety policy....geof-near Cincinnati

[Patrick]

Geof. so were you supposed to blow it down overnight?
If anyone knows of how you adjust the low air alarm setting please advise. I thought there was a forum for everything...I can't find one for big trucks.

[geof]

Patrick...I have always blown the truck down everynite to drain the moisture out of the system/dryer....It takes 2 minuites to blow down/blow up and do a walk around the truck at nite and in the morning before going over-the-road the next day.I do it as part of my pre/post check along with making sure my wheels are choked front and rear. It also gives me time to check tires and for any liquid leaks or lite bulbs out....I got used to it when I drove over the road in the 70's and the 80's....now I do it automatically/by habbit/obsessionly... One thing you guys need to do is check those compartments doors to make sure they are closed/locked properly....I looked at a Kingsly yesterday and one compartment door was not closed properly....Our new village Firetruck has a alarm/lite warning system so all compartments must be shut and locked when moving the truck....It is made by using magnetic contacts off a bugler alarm system and very effecive as a truck driver[engineer] can't do a walk-a-round before heading off to a fire.....also helps to indicate that all the doors/personel/equipment are aboard as the driver checking all that is almost impossible because of the noise of the electronic radio noise /Q-"SCI-REEN" and air horns....might be a thing you guys might want to install on your larger motorhomes to monitor your kids/wife safety and to check if doors are ajar or windows open....and also to supprise anyone that your dog doesn't hear when camping...after all not everyone is honest/trustworthy as we are.....as yes before you all ask-"I'm packing" for my protection-I heard of a guy fending off a black bear attack with a marine flare pistol.....FWIW.....geof-near Cincinnati

[Don in E Texas]

I agree -- about 60 pounds is where the "low air warning" light/buzzer comes on.

My bus conversion has 4 air tanks and 1 air gauge -- My Freightliner Class 8 Conversion has 3 air tanks and 2 gauges. The truck will show 100 pounds or more on each gauge, but the main tank can be empty of air (as checked by dumping air via manual dump valves). The bus will show zero air when I still have air in two of the tanks. Guess it depends on where the gauge is installed in the air system. On my bus, I can see the compressor cycle between 90 and 130 pounds; on the truck one gauge sits around 130 while the other is at 115 --- and they don't move very much unless I apply a LOT of brakes. (They go to zero when I drain the tanks fully)

Air bags on the bus -- tag axle will empty out in about 6 hours --- (no check valve in the tag axle air system). All other air bags take about a week to show the coach to be somewhat lower so I run the bus once a month to get back to level once again (they all have check valves).

Have not noticed the truck air bags going down, but I don't have any weight on it either until hooking up my little trailer.

Will your truck pass the normal "Air Brake Test" that you perform prior to starting out in the morning on a trip?

don

[Patrick]

What "test" would that be Don?

[Don in E Texas]

Air Brake Test.

Same test that a license examiner would give someone taking a drivers license test in a vehicle with air brakes. Same test that should be done prior to setting out each day --- test can help spot many air leak problems. One example: my used Freightliner tested fine for 2-3 weeks after I purchased it. One time it showed a small loss of air ie it failed the air brake test --- took truck in and had one of the rear brake air chambers replaced - was leaking when brakes were "off" -- no leak when "on".

You can check various State Commercial Drivers License Manuals on-line to see how it is done - that is one source. -- or someone on the forum might have good verbage of the test and can post the required steps - test is all done from the drivers seat.

don

[Patrick]

Tell us how you test yours!!

[Don in E Texas]

Patrick:

I re-read my post and I did a poor job in answering a question, I come across as a complete A** Hole!! Sorry that I did not fully answer your question --- if I could cut/paste on this forum I'd supply the exact info. Let me see if I can do a better job (I don't consider myself as a complete AH <grin&gt

So here goes (and others, please feel free to jump in --- this is how I do it on both my bus and truck).

==============

Chock the vehicle to prevent it from rolling!

Fully charge the air system -- (125#)
Turn off engine, release parking brake and time air pressure drop. Should not be more than 2# in 1 minute. (note: my truck failed this when one air brake canister was leaking)
Apply service brake (brake petal) (90# on brake application gauge if your vehile has this feature). After initial pressure drop - time for 1 minute -- no more than 3# should be lost. (note that these figures are for truck only -- not truck with trailer with air brakes)

Turn key "ON". engine "OFF". Rapidly depress the brake petal up/down while observing the air gauge. Warning light/flasher/buzzer (whatever your vehicle might have) should come on when pressure reaches 60#.

Continue the rapid on/off of the brake petal while observing the air gauge. The emergency parking knob should pop out when air pressure is between 20 - 40 #.

Start engine and observe how fast the air pressure builds up. Should reach 85 - 100 in about 45 seconds. This depends on vehicle, number and size of air tanks, etc.

There are also checks for the governer cutin/cutout pressure.

It takes less time to do the test than it does to read it. But I'd recommend getting the straight info that is available in various Drivers License Manuals.

Hope this helps.

Also it is good to note your vehicle has three brake systems:
Service (foot petal)
Parking (pull out knob)
Emegrency (knob comes out when air pressure is between 20 - 40#

don

[Patrick]

Thanks Don!! This is priceless info! I will print and laminate this test and execute it before every outing. I learned something else today...the low air alarm is not ajustable. There is a sensor on the air brake system that controls when the alarm goes off (supposed to be 60-70 psi). I was told to look under the hood near where the brake pedal comes through the firewall for a 1/4" diameter sensor with either 1 or 2 wires. These sensors run $4 at a local truck supply. Thanks Don, this forum will soon be a wealth of information for newbies like myself!