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Air brakes questions again

So attached is a picture of the air gauges after they have bled down.  This is after 3 days. As you can see the pressure is just around the 30 to 40 mark. Should I be concerned?  Is there a fix I have not researched to fix this?



Peter    Alberta Canada
'98 U320 40'  Build 5359 M11 450 HP, Aqua hot, Blu Ox

Re: Air brakes questions again

Reply #1 –
My guess would be, if they drop below 60 there's a check valve that's not doing it's job.  Mine do occasionally but fortunately not very often.
Robert and Susan
 1995 36' 280 WTBI 8.3 3060r
 1200 watts on the roof, 720 Ah of lithium's
 Build # 4637. Motorcade # 17599
        FMCA  # 451505
        18  Wrangler JLUR

Re: Air brakes questions again

Reply #2 –
My coach also drop to 30 psi after a couple of days and Eventually will go to 0 PSI  And that is normal it is almost impossible to get a system airtight You can read in the Owners manual and it will give you how much air that you will probably lose and it's in hours not days
 It maybe be air tight new but not for long and I say maybe if your lucky
Rick & Hilda looking forward to full- timing one day for now couple of months at a time
1999 U270 3602
Built number  5530.  Feb 1999            Motorcade  number 18438
8.3 Cummins Allison six speed with brake  retarder
Purchased Nov 28 2019

Re: Air brakes questions again

Reply #3 –
Rick answered your question. I wish mine had 30lb left in 3 days but I'm thru looking for the air seeps, What's important is when you apply the foot brake the air doesn't keep escaping after the initial fill of the brake chambers which takes about 5 to 10 lbs each application. It is rare for a coach to not seep down just sitting. See one every now and then but it won't likely last and Isn't important.
Dub McBride 1996 270

Re: Air brakes questions again

Reply #4 –
Static Air Loss,
"The loss rate should be no more than 2 psi in one minute for single vehicles"
                                ************************************
The proper procedures for inspecting the air brake system are as follows:
Test Air Leakage Rate (Static check)

With a fully-charged air system (typically 120 psi), turn off the engine, chock the wheels, release (push in) the parking brake button (all vehicles) and trailer air supply button (for combination vehicles) and time the air pressure drop. After the initial pressure drop, the loss rate should be no more than 2 psi in one minute for single vehicles and no more than 3 psi in one minute for combination vehicles.
Test Air Brake System for Leaks

With parking brake, (all vehicles) and trailer air supply button (for combination vehicles) released (pushed in), apply firm pressure to the service brake pedal. Watch the air supply gauge and listen for leaks. After the initial pressure drop, the loss rate for single vehicles should be no more than 3 psi in one minute and no more than 4 psi in one minute for combination vehicles. If the air loss rate exceeds these figures, have the air system repaired before operating.
Test Low Pressure Warning Alarm and/or Signal

Turn the key to the on position. Rapidly apply and release the service brake pedal to reduce air tank pressure. The low air pressure warning signal must come on before the pressure drops to less than 60 psi in the air tank. If the warning alarm/signal doesn't work, you could be losing air pressure without knowing it. This could cause the spring brakes to activate suddenly. Only limited braking can be done before the spring brakes come on.
Check That the Spring Brakes Come on Automatically.

Continue to rapidly apply and release the service brake pedal to further reduce air tank pressure. The trailer air supply button (if it is a combination vehicle) and parking brake button should pop out when the air pressure falls to the manufacturer's specification (usually between 20 to 40 psi). This causes the spring brakes to come on.
Check Rate of Air Pressure Buildup

When the engine is operating at 1800 RPM, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. (If the vehicle has larger than minimum air tanks, the buildup time can be longer and still be safe. Check the manufacturer's specifications.) If air pressure does not build up fast enough, your pressure may drop too low during driving, requiring an emergency stop. Don't drive until you get the problem fixed.
Test Service Brakes

Wait for normal air pressure, release the parking brake and trailer air supply button(for combination vehicles), move the vehicle forward slowly (about 5 mph), and apply the brakes firmly using the brake pedal. Note any vehicle "pulling" to one side, unusual feel, or delayed stopping action. This test may show you problems which you otherwise wouldn't know about until you needed the brakes on the road.

Source: 49CFR383.113

Copied and pasted from here: CDL Pre-Trip Inspection: Brake Check | CDL Digest
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Air brakes questions again

Reply #5 –
Your protection valves are weak if it stays at the pressure in your pictures. If it keeps dropping the next day they are failing. I read lots of posts that you cannot worry about the air leaks, just as posts say the dash air will never work. I have my coach leaks down to holding over 100psi for 3 days. Case in point last week the DW and I went to dinner after 4 days at the campground and upon returning when I hit the remote to lock my car the Hadley's went off and kept blowing. After realizing that the remote could not be causing it, I looked in the window of the coach and one of the dogs was standing on the steering wheel watching us. My crane only used air for brakes and I have it holding 120 psi. for weeks. Air leaks can be stopped just not something most people want to put the effort into. As mentioned before there is no need to stop the small leaks but it can be done.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Air brakes questions again

Reply #6 –
You May need to be the next one that gets under mine for air seeps Chuck.. I'll be much obliged and will carry water for ya.
Dub McBride 1996 270

Re: Air brakes questions again

Reply #7 –
Ok.  Where are the protection valves located and are they an easy swap out  I am not sure where to get them here in Canada either but I suspect a heavy truck shop or such?
Peter    Alberta Canada
'98 U320 40'  Build 5359 M11 450 HP, Aqua hot, Blu Ox

Re: Air brakes questions again

Reply #8 –
The Protection Valves are located above the front axle near the front and rear dry air tanks are located. They look similar to a miniature propane regulator because they have an adjustment screw/spring. Mine were leaking such that the air leak could be heard standing beside the coach. Once under the coach I could feel the air blasting out the hole for the adjustment screw. The way mine air hoses are plumbed, I would have had to dismantle and reassemble several pieces to replace the protection valves, so I disassembled the protection valves and replaced the seal rubber surface with a cut down piece of a bicycle repair patch. The release pressure increased to 70psi (was 60psi). In the eleven years I have owned my coach I have done this repair twice.
Wyatt
96 U320 40 WTFE, build 4943
84 Toyota Supra towd
2015 Jeep Wrangler towd
Victoria, BC, Canada

Re: Air brakes questions again

Reply #9 –
You should be able to get them at a truck shop
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Air brakes questions again

Reply #10 –
Quote from: Dub –
You may need to be the next one that gets under mine for air seeps Chuck.. I'll be much obliged and will carry water for ya.
I'll bring mine over and we'll "let" Chuck make a day of it - he can do a "two fer one special".  I'll bring something stronger to mix with the H2O.

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 brakes questions again

Reply #11 –
Quote from: dicksop –
Where are the protection valves located and are they an easy swap out.
Search for "protection valve" using the Forum search tool.  Order results by "most recent".  You will find some good info.

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"