ISX air compressor service life/ unloader valve

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by SemperFiServices, Jan 22, 2020.

  1. SemperFiServices

    SemperFiServices Medium Load Member

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    Jan 29, 2013
    Indianapolis, IN
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    I've got a 2015 Intl with an ISX. It's an old Knight truck I'm working the bugs out of. So I've put a brand new air dryer on it, but the air compressor still has a habit of dropping very low, but only at idle, not while driving. I've run PB blaster through it like Cummins does with WD-40 to revitalize the reed valve, but either I didn't use enough or it's just worn out.

    I guess my question is, should I rebuild the head, replace the head, or replace the whole compressor? It only has 535,000 miles, but just over 17,000 hours run time. I'd like opinions from those with more experience than I, thanks guys!
     
  2. QUALITYTRUCK

    QUALITYTRUCK Road Train Member

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    Jun 14, 2009
    romulus,mi
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    Replace the whole head with a new one. You can order on internet for under $300. Make sure that you don't have a break in main air line. They like to go bad where metal line joins to braided line.
     
  3. Goodysnap

    Goodysnap Road Train Member

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    Jul 12, 2017
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    I agree with @QUALITYTRUCK .

    Cummins procedure calls for plain ol' ATF to flush the unloader valve of carbon. If you know the oil services have been regular, the bottom end of the compressor will likely outlast the engine since they are lubed with the same oil.

    Replace both the stainless braid and the cloth discharge line all the way to the dryer. Good Chance there is either a leak you cant hear where the cloth starts or hose separation internal where you cant see it.
     
  4. SemperFiServices

    SemperFiServices Medium Load Member

    366
    209
    Jan 29, 2013
    Indianapolis, IN
    0
    I was having the same problem, where I had to beat on the compressor, spray lube in the inlet etc, to get it to build air- always only a temp fix.

    I finally just bought the head rebuild kit from Cummins for about $225, and rebuilt it. I had to pull the power steering pump and compressor, but it was surprisingly easy with basic hand tools. I must've scraped a good 1/4 cup of soot outta the head passages, but cleaned both halves really well, took out the unloader valve, cleaned it and lubed the o-rings, rebuilt it and used the torque specs in the manual, and not a hiccup since.
     

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