M939 Air tank help

Spyderman

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Hey guys I need some help. Looked through the TM and didn't see it. Probably over looked it. I need this sensor for my air tanks on the passenger side.



I thought about just silicone it back in. But I would like to get a new one. But I don't know what it is called or where to get one. Thanks
 

rosco

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I don't know what it is, other then a pressure switch of some kind. Maybe for a buzzer? Usually there is a number, close to the end of those wires. See what it is and look for it/where it goes, in your wiring diagram.... Take the rest of it out and see what it is (I would use a deep socket). Clean it, and see if it works. A few more clues, would be nice too.
 

Andyrv6av8r

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It's a low air pressure switch that turns on your buzzer and low air light on the dash. One on primary and secondary tanks.
 

WSm925a2

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Curious, that's tank number 3, when you drain your air tanks, do you get air from that tank? I get very little and I noticed that when truck is not running but still on (battery still on) I get one blow of the horn even though both primary and secondary tanks are at 120 psi. Trying to figure this out.
 

Csm Davis

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Curious, that's tank number 3, when you drain your air tanks, do you get air from that tank? I get very little and I noticed that when truck is not running but still on (battery still on) I get one blow of the horn even though both primary and secondary tanks are at 120 psi. Trying to figure this out.
Sounds like you need to PM your whole air system, I would start at the drain on that tank and disconnect it from the tank and clean it out and then do all the rest of the drains, then start on the feed lines and check valves, you are going to find lots of rust and crap.
 

Floridianson

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No just go too any truck parts place and get a 10 buck low air pressure switch. I can not find the thread where I had all the info. Here is the pic where I just used the military ends. Our search is not very good I can not even find my own post's from the past.
 

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Floridianson

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Did the 939 series put the one way check valve between all the tanks like the Deuce? This would stop anyone tank from draining all the others. Been awhile since working on the 939 and CRS is in full bloom.
 

Artisan

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Sounds like you need to PM your whole air system, I would start at the drain on that tank and disconnect it from the tank and clean it out and then do all the rest of the drains, then start on the feed lines and check valves, you are going to find lots of rust and crap.
I think I can SuperSize that;
What happened when you did your C.O.L.A.S. test before you drove it for the first time?

:tank:
 

IsaLandr

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First time?

Go back to CDL school

It is supposed to be done daily
For any vehicle driven daily, sure. For any vehicle driven regularly but not daily, then before every use. Or, for vehicles driven sparsely, performed at regularly scheduled maintenance and upkeep intervals, as well as before every use.

However, I think I see where Artisan was going with this, and I too am curious for the answer. What happened when the first test was performed when the truck was first acquired, before it was driven? Much will be told from the results of that very first test.
 
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quickfarms

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Curious, that's tank number 3, when you drain your air tanks, do you get air from that tank? I get very little and I noticed that when truck is not running but still on (battery still on) I get one blow of the horn even though both primary and secondary tanks are at 120 psi. Trying to figure this out.
This posters truck may have passed the COLA test.

It is sad that the hole CDL testing does not address draining the air tanks. At least in California.

This posters truck probably has three issues. The first issue is the air dryer is plugged and needs to be serviced. This has allowed water, and debris, to accumulate in the air system. The water may have led to some rust in the system. This is plugging the tank drain and all the tanks and drains need to be cleaned. The issue of the horn is probably related to the dirt and debris affecting the valves supplying the horn.
 

Floridianson

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Yes service the air system. The draining of the tanks has an order to check the check valves. On the Deuce it is outboard first and the inner tank should hold all of it's air. If not then the check valve is bad. Same with the 939 series has an order to drain to check the check valves.
 
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