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Thread: Lost CTIS and all air driven stuff ?

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    2 Star General 1951M1078's Avatar
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    Default Lost CTIS and all air driven stuff ?

    Have had a problem with the CTIS working and not working. But Now the hole air system is down ? Tanks will not build air ? Pump was good. No air leaking up until being parked for about 30 days. Today I took some time to take a look because the driver side tire went flat ? Never had this before. Checked the tanks all had air pressure.How much ? gauge read 120+- at dash. Was trying to check air to cab but nothing ? Ran motor after draining the tanks and nothing ? Did not refill ?

    So what manual do I need to use ? Having a hard time finding out how it works.

    Thanks, Randy
    1960 #53 M151 (sold)
    1996 M1078 (LMTV)
    2007 4 Door JK

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    General 319cssb's Avatar
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    Does the power steering still work?
    if so, it may be the governor or worn piston rings on the air compressor
    I will either find a way, or make one!
    --------------------------------------------------------------------------------------------------------
    I hate people, who use big words just to make themselves look perspicacious.

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    2 Star General Andyrv6av8r's Avatar
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    Start with the compressor and work aft.
    M923A2 2012 Rebuild, aka Romeo-Mike, aka HellCat

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    M1079 LMTV, Shrek, sold to kenet3621

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    If gauges on dash read 120 range as you said then compressor is probably good. A stuck Protection Valve would cut off air to CTIS and other secondary functions like cab lift.

    Dash gauges read the two brake tanks, the two toward front of truck. The 'wet tank' is the smaller rear tank. It fills first, so if other two tanks are full, wet tank probably is too. Verify air there by opening drain valve. If lots of air comes out then conpressor is good. Did the system 'pop off' when full?

    The Pressure Protection Valve (over pressure valve) is that regulator-looking thing on the rear of the wet tank. Disconnect one of the output tubes from it and verify air there. If not, try adjusting it a little. Maybe it is stuck. These are easy to disassemble and clean. They can also leak out from under the cover assembly and not open.

    You are probably looking at a tire repair too.
    Last edited by tennmogger; 01-31-2019 at 07:06.
    1952 M-38
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    1957 Unimog 404 flatbed, French NATO (Germany)
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    1988 Unimog U-1300L with 10' NCO Alaskan Camper
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    4 Star General NDT's Avatar
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    Mine did this, the air dryer sneeze valve was stuck open.

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    General 319cssb's Avatar
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    The OPs post is a bit inconclusive. But i think in the end he said that he drained the tanks and then there was as no air pressure.
    I dont know what up with the question marks. Is he asking or making a statement and just doesnt use the question marks in the right location.
    I will either find a way, or make one!
    --------------------------------------------------------------------------------------------------------
    I hate people, who use big words just to make themselves look perspicacious.

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    4 Star General porkysplace's Avatar
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    When was the air dryer last serviced ?

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    2 Star General 1951M1078's Avatar
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    The hole dam thing is one big "Question mark ". The "?" is more a ,what the **** is going on for me.

    Dryer is the new style and new about a year ago. Maybe 40 miles on it. The pop off valve was working right up to draining the three tanks.

    Question . What turns on the air compressor ? I thought it was the lack of a air pressure and at the limit valve. (may not have the name right) Could this control be stuck in the pump off position ?

    As for the power steering,I will need to try it. It did up to being parked.

    When the wet tank had air I could not get air flow from the big or little line. But it did leak ahead of the control valve as I was getting ready to remove it to take a closer look. That is when I drained the tank. This is also the point when I fired up the truck to see about air flow and got nothing.

    And I still need to know what "TM" to use. Please.
    1960 #53 M151 (sold)
    1996 M1078 (LMTV)
    2007 4 Door JK

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    In the back of the 20-1 thru 20-5 manuals there are schematics. The air system drawings are in there with the rest of the electrical info.

    If the power steering is bolted on the back of the compressor and gets its drive from the compressor. if it is working that means the compressor is at least turning and the drive from the engine is OK. The air compressor output is controlled by the governor located on top of the compressor head which monitors air pressure at the tanks and activates and de-activates the unloader valve at the compressor(there are two small air lines that perform this monitoring and control). This unloader cycling also activates the purge on the air dryer(tanks fill, unloader stops the compressor from delivering air, dryer purges).


    Compressor feeds the wet tank, wet tank feeds the others. if you have 120 PSI on the pri and sec tank gauges, the wet tank should also be full... Wet tank protection valve feeds CTIS/fan and cab suspension air until the pressure in the tank drops to around 85 PSI(protects air supply in the tank to feed the brakes). The cab raise/lower/tire crane air that drives the hydraulic air operated pump is drawn directly from the primary and secondary tanks, so if you have pressure on the gauges these should work.

    Do you have an air compressor? If you do you can connect air to the emergency port at the front which will fill the wet tank directly(and the rest of the system) so you can look for leaks without having to overcome engine noise. and see if the rest of the system functions/cab opens.


    Troubleshooting air compressor supply, as suggested, start loosening fittings at the compressor and work your way toward the tanks...

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    4 Star General Steel Soldiers Vendor Suprman's Avatar
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    If the air compressor is indeed not making pressure I would check the governor first. Its mounted on the compressor. And the unloader could be stuck open. The lubricant can harden over time and cause issues. The unloader can be rebuilt without removing the compressor. Its a dual piston compressor. Pretty unlikely that both pistons go bad at the same time.

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