Bendix AD IS Purge air leak

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Rockslyde, Sep 24, 2021.

  1. Rockslyde

    Rockslyde Bobtail Member

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    Feb 3, 2019
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    I've been searching the web, looking for as much information as I can get on the Wabco compressor. Or anything else that might help me on this. Apparently, this isn't a common problem. I actually went to a dealership and was told to change the desiccant filter and purge valve. I had my doubts at the time, because the purge valve wasn't leaking at all while charging, or when the engine was shut off. But I did what he said, it didn't work so I bought a whole new dryer and nothing changed. don't think the problem is with the dryer itself. I'm thinking I'll have to take it a more qualified mechanic.
     
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  3. Goodysnap

    Goodysnap Road Train Member

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    Please update when you find the issue as I am curious. I have exhausted my ideas. Guess I would need the truck to see whats up.

    Its something stupid, guarantee it.
     
  4. Rockslyde

    Rockslyde Bobtail Member

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    Feb 3, 2019
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    Ok thanks for all your efforts. I crawled under the truck trying to find an air leak. I can hear something very very small. I haven't pinpointed it yet. I have a couple of very small airleaks on the fire wall, but they've been there for while. I keep a spray bottle with me on the truck, but it's not a magic cure all. Space is very limited on these 579's . I'll have to cut away 20 or 30 zip ties and do some digging around. I've had ringing in the ears for 40 years, so that further complicates things. I'll mess with it tonight for awhile. Start out fresh in the morning if I can't find anything tonight
     
    Goodysnap Thanks this.
  5. Goodysnap

    Goodysnap Road Train Member

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    The cloth discharge lines are common for leaking. Usually right above the trans right after the prebent steel tube directly off the compressor. This will always result in a slow build complaint.

    I'm curious is the leak from the purge valve pulsing like the compressor pumping or is it a continuos steady leak?

    I would still call Bendix on Monday to see if they have ideas I havnt thought of. Its a free call and they are very helpful.
     
  6. Rockslyde

    Rockslyde Bobtail Member

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    Feb 3, 2019
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    I didn't notice it pulsing before, but yeah I just checked it. It is pulsing like the compressor
     
  7. Goodysnap

    Goodysnap Road Train Member

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    I dont think the compressor is unloading. I would most definately suspect a broken or stuck unloader valve in the compressor head. Disconnect the unloader line @ the compressor. Make sure good unload signal is reaching the compressor and the line is not blocked?
     
  8. Rockslyde

    Rockslyde Bobtail Member

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    Feb 3, 2019
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    Hey, I got my truck back from the dealership a couple of days ago. First day, they couldn't figure it out. Checked for leaks, found none. Second day, they called Bendix and was told that a Bendix dryer would fix the problem.
    Bendix said the internal components on the after market dryer weren't calibrated as precisely as the Bendix. (Yeah right) It didn't fix the problem. They tested the compressor and found that it was functioning properly. Called Bendix again and was told to replace the main air line from the compressor to the dryer. (At that point what else could it be, right?) Bingo. Problem solved. Air line was about $130.00 .
    I had sprayed that line looking for a leak and so did the guys at Kenworth. I didn't see any bubbles, but apparently something about the old line was bad. I had considered replacing it early on, and being a cheapskate, It came back to bite me.
     
    Goodysnap Thanks this.
  9. Goodysnap

    Goodysnap Road Train Member

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    Wierd...??.normally the discharge line would have nothing to do with dryer purge.

    Slow build times maybe?

    They are common to leak......right where the cloth hose starts above the trans

    Thanks for posting a fix
     
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