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Old 05-31-2016, 08:41 AM   #1
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Mechanical rear air suspension.

My bus is equipped with a mechanical rear air suspension.. it makes for a nice ride.. but it continues to operate after I turn off the bus... and over a period of about an hour or two runs my air pressure down to 65 PSI at which time it looks like some sort of mechanical regulator valve "cuts off" and kills the air to the suspension...

of course this means I have to wait for my air to build back up everytime IO want to drive the bus..

is this normal operation or was there at one time likely some other valve installed?

some may have electronics related to their air suspension, mine is Purely mechanical in nature..

-Christopher
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Old 05-31-2016, 08:43 AM   #2
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Quote:
Originally Posted by cadillackid View Post
My bus is equipped with a mechanical rear air suspension.. it makes for a nice ride.. but it continues to operate after I turn off the bus... and over a period of about an hour or two runs my air pressure down to 65 PSI at which time it looks like some sort of mechanical regulator valve "cuts off" and kills the air to the suspension...

of course this means I have to wait for my air to build back up everytime IO want to drive the bus..

is this normal operation or was there at one time likely some other valve installed?

some may have electronics related to their air suspension, mine is Purely mechanical in nature..

-Christopher
I've only had one vehicle with air ride and its my bus. Yours sounds like mine though. They air down once you shut off the bus. Mine does so fast.
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Old 05-31-2016, 08:48 AM   #3
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does yours air both tanks down to 65 and then stops there? my bus will hold air for days at 60-65 PSI once the air suspension shuts off..

I was out trying to chase down air leaks tinking thats why my tanks were going town and it turns out I could hear a tiny little air "motor" running while I was working under the bus.. its last an hour maybe 90 minutes.. then shuts off and the air shocks go nearly flat then... once i start the bus.. my air alarm is beeping.. and I'll notice the gauges build very slowly for the first few PSI as it is re-filling that suspension.. then the pressure goes up quickly...

-Christopher
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Old 05-31-2016, 08:59 AM   #4
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I've got the same thing, I have to wait about 1-2 minutes for air pressure to come back up after not driving for awhile. It doesn't really matter for me as long as I do get air pressure back. Air brakes plus air suspension on mine
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Old 05-31-2016, 09:36 AM   #5
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Most likely there is an air leak somewhere and if indeed there is a 'motor' continuing to run after the engine shuts off then the leak is probably in one of the air bags which is why it's continuing to attempt to level the vehicle. Of course at 60psi an air brake equipped vehicle is now in warning mode because it's apparently not recovering air fast enough to continue providing brake functionality so it is not surprising that the air ride system would then disable to preserve air for brakes. It is however positive that once it bottoms at 60psi it stops, meaning there doesn't seem to be any other air leaks in the system.

My instinct would be to not worry about it because you could spend a lot of time and money and aggravation chasing it down. If it recovers quickly enough after you restart the engine then it can't be a very bad leak.
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Old 05-31-2016, 09:57 AM   #6
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thats one thing I havent done is test for air leaks in the air suspension itself.. thats a good idea just to see..

it looks like the cut off valve they installed is adjustable.. I cant find a part number on it to look it up.. but im going to seek it out.. I may just disable the air suspension at 90 PSI if I can set that valve up and not affect the max pressure assigned to the air suspension.. it may also be regulating the pressure to it at 60 and of course I dont want to alter that.. I need to read more before i get the wrenches on it.
-Christopher
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Old 05-31-2016, 10:13 AM   #7
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Yeah, my pass side rear air bag is garbage. Cracked, dry rotted... Its gotta be changed before going across the country for sure.
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Old 05-31-2016, 10:33 AM   #8
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my bags look good.. but looks are decieving! but there is a bit of rust around the control block.. could be a leak there.. i'll spray that all down when i get back home and have 120 PSI in the tanks..

out gettin 6 brand spankin new paws on it now!! goin up from 10R to 11R and looks like its all gonna clear nicely and still have good clearance at the tandems and for steering..

-Christopher
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Old 05-31-2016, 10:34 AM   #9
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oh and I just had another DUH! moment.. that air suspension is part of the Chassis and not the carpenter so it should be in my Service manuals.. so if I RTFM I probably can figure it out..

-Christopher
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Old 05-31-2016, 01:26 PM   #10
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I have driven quite a few air-ride trucks over the years. The air suspension on my Volvo "airs up" at around 80 (as does the cab) ... and after shut down, it can be heard adjusting itself for several minutes. The air system on that truck has leaks, it will go down to almost nothing overnight. The compressor works well, so we haven't bothered to diagnose it and with nearly 770K miles it isn't likely to be in the fleet much longer.

I'd say your air suspension is "normal behavior", but if you wanted to try to eliminate the leak, my first suspect would be the "leveling valve" as this is a common failure item.
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