Bed Not wanting to raise on first try, extremely slow.

Discussion in 'Western Star Forum' started by visvolt, Feb 5, 2021.

  1. visvolt

    visvolt Bobtail Member

    Dec 16, 2006
    I haul coal in a 2020 4900XD with a DD15, Allison 6 speed auto. Maybe 4 months after my boss ordered it, the bed started acting funny. When I went to dump my load, I push the pto button to on, pop the tailgate and push the bed lever into "raise" and give it a little fuel and nothing happens. I tried all the basic stuff, checked the actuator/plunger to make sure it wasn't clogged... but on the automatics, it's near the frame above the front axle and never gets muddy. I shook the air line connections, and then hopped back in and the bed raised. So we thought that was the problem. Until that didn't work any more. So my boss ordered a new diverger and that didn't help it. So then he orders a new bed pump, we throw it on and for about 2 1/2 days it works like brand new then starts doing the same thing. They thought the gear ratio might be wrong, but I don't think that explains it.

    I don't know what fixes it, but when it won't go up the first time I try it, I will flip the pto in and out, then push the bed lever back and forth and retry it. I'll do this 2 or 3 times and it starts raising most of the time. But every now and again, that doesn't work and then i will either pump the air down and try it again and some times that works. Once I just put the truck back in gear, drove it forward about 5 foot, then backed it up and stomped on the brake to shake some of the weight off, and after I did that and tried to raise the bed it started raising. But every time it goes up it is extremely slow. Even if I raise the RPMs to an ungodly amount, the bed still raises so slow.

    I mainly only driven Mack RDs and DMs prior, and don't have any real mechanical knowledge, I just greased my truck and changed flats... thats about all i've done on my own. But I can't help but to think its an airline issue. On the Western Star 4900 XD with automatic trans, the PTO button is electrical, the bed lever is air, and of course hydraulic oil to raise the jack. So, could a blocked air line in the control box be causing this? Anyone have any idea what I'm talking about? It sucks fighting with the bed all day long every day in this new truck. Everyone has to wait on me to dump if im in the way, or if we can dump multiple trucks at once, 2 other trucks can dump beside me and leave before I get my load off.

    The mechanics and owner seems to not have any idea what to do for it and as long as im making it work, they're okay with it. But any driver here knows, the things we have to fight with all day long on the job can drive ya nuts.
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  3. NightWind

    NightWind Road Train Member

    Nov 11, 2006
    Sunny South, AL
    Have you checked to see if the hydraulic line is tight? Take it completely loose and reinstall see if that helps. Some times they get "vapor locked: for lack of a better term to call it.
    Also have you checked to see if the cylinder auto bleeder is working properly? Some times they get stopped up.
  4. AModelCat

    AModelCat Road Train Member

    Jul 7, 2015
    You gotta find a mechanic who actually understands hydraulics. Lot of truck guys don't. You've got to get the pressure and flow checked with a flowmeter. See what that pump is producing.

    Was the truck upfit with the dump body and PTO at an upfitter shop or done in-house?

    Does it raise slow when empty as well?
    NightWind Thanks this.
  5. Happily Retired

    Happily Retired Road Train Member

    Apr 16, 2014
    high plains colorado
    A 2020? We're doomed,,,it's a safety issue and I wouldn't screw around. That truck would be sitting crossways in the dealer entrance with all the tires flat,,,sorry, I'm trying to be more positive, but I hear stuff like this, new trucks costing 6 figures, and it doesn't work? That, to me, is simply unacceptable.
  6. Joyce's Volvo

    Joyce's Volvo Bobtail Member

    Jun 28, 2016
    Sounds as if the valve isn't opening fully,( the spool isn't going fully to the proper position). I'm not familiar with the new and improved version ( often new and improved ain't better ) but, on the older ones ,that's where I'd start looking.
    NightWind Thanks this.
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