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Old 04-23-2019, 03:11 PM   #1
Mini-Skoolie
 
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Question Air leak underneath

This morning I started the bus and I noticed a hissing noise coming from under the bus. The air gauge on the dashboard reads 110- 120 there is no air for the door, seems like the air brakes work, but the air suspension bags wont fill up.
I tracked down the leak and took a picture of the part where its coming from.
I drive a 2002 Thomas with a 3126 and its the 9 window flat nose.
I am not sure if its some sort of a valve stuck open or broken. Any help greatly appreciated. Thanks!!


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Old 04-23-2019, 03:20 PM   #2
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Picture doesn't show a leak, where is it leaking?
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Old 04-23-2019, 03:35 PM   #3
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Picture doesn't show a leak, where is it leaking?
I posted the wrong one the first time. Check now. This part is vertical to the ground and seems like there is a air hose coming in and one going out. It does not leak from the hose fittings. Feels like the the air is coming from the hexagonal cap looking thing thats on thread.
Thanks for the reply.
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Old 04-23-2019, 03:51 PM   #4
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Maybe some kind of proportioning valve but I don't think so.
Normally don't see shutoff valve in a brake system cause it would be to easy for a mechanic to leave closed.
Bleed the air off at the tanks and pull the cap to see what's behind it or just pull that piece and clean it off to find the numbers on it
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Old 04-23-2019, 04:48 PM   #5
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Disassemble the end and see what you're dealing with. You might find it repairable without new parts.
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Old 04-23-2019, 05:31 PM   #6
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Sounds like a protection valve - which is supposed to be "closed" until the air system reaches 60-80 PSI, at which point it will open to provide the air bags, door, air seat, etc. with air pressure. The brakes, being such a critical system, will (should) **ALWAYS** get full air pressure, regardless how much is available. This includes the parking brake, but the knob may not stay pushed in below 60 or so (the way it's supposed to be) and the brakes may not release (or they will drag) under 60 or so.
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Old 04-29-2019, 03:06 PM   #7
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Looks like a ton of undercoating up there. I’d give that part a good wire brushing by hand, then take it halfway apart. Probably a tired or crusty o-ring in there letting air escape.
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Old 04-29-2019, 11:00 PM   #8
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I heated it up with the hair dryer and sprayed some wd40 inside. Then as the bus was idling I tapped it a few times and it seem to fix the issue. Its been working pretty good.
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Old 04-29-2019, 11:16 PM   #9
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Originally Posted by madhat View Post
I heated it up with the hair dryer and sprayed some wd40 inside. Then as the bus was idling I tapped it a few times and it seem to fix the issue. Its been working pretty good.
WD-40 and a BFH solves most problems.
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Old 04-29-2019, 11:19 PM   #10
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WD-40 and a BFH solves most problems.
And if that don't work, get a bigger hammer. If that don't work, it's an electrical problem.
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