Air dump/ rough ride

Discussion in 'Trucks [ Eighteen Wheelers ]' started by jthomsonmusic, Oct 1, 2019.

  1. jthomsonmusic

    jthomsonmusic Bobtail Member

    4
    2
    Aug 28, 2019
    0
    I have a 2016 cascadia daycab twin screw. Whenever I hit the dump switch, drop a trailer, and pull out, my power axle (front) will spin the tires. It seems as if the rear bags have more air. I’ve already adjusted the ride height to factory spec. Also I believe this is causing a rough ride over bumps.
     
  2. Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  3. lester

    lester Midwest's #1 Feed Hauler

    2,808
    7,451
    Jan 2, 2012
    NW, Iowa
    0
    First thing if you have a true normal twin screw tractor, not just one live axle with a dummy axle, you don't have a power axle. With the power divider unlocked which ever tire with the least traction will spin, could be front or back left or right. With the power divider locked one wheel on the front and rear axle will spin. Could be either side. It doesn't criss cross or anything, which ever wheel with the least traction will spin.

    Now you said with the dump valve dumped it seems like the rear bags have more air in them? That shouldn't be with the bags dumped. Dump the air and tap on your bags with your hand. The should all be soft..

    If you are having problems spinning while pulling out from under a trailer lock your power divider in or don't dump your bags
     
    Swine hauler, x1Heavy and pushbroom Thank this.
  4. 201

    201 Road Train Member

    11,172
    22,655
    Apr 16, 2014
    high plains colorado
    0
    lester is right. The driving axle will spin unless the power divider is locked. Next time, pull away from the pin, then drop the air.
     
    x1Heavy Thanks this.
  5. Numb

    Numb Crusty Curmudgeon

    3,368
    6,529
    Jan 30, 2012
    Charlotte, N.Carolina
    0
    wait a bit for the bags to fill some.
     
  6. jthomsonmusic

    jthomsonmusic Bobtail Member

    4
    2
    Aug 28, 2019
    0
    I believe I understand now. Thanks for the reply. I just checked my bags after a long drive and I have more air in the rear bags compared to the front. I’m at factory spec ride height. I’ve also tried lowering the height and raising it. Same result. What could be causing the back bags to over inflate? A stuck check valve?
     
  7. lester

    lester Midwest's #1 Feed Hauler

    2,808
    7,451
    Jan 2, 2012
    NW, Iowa
    0
    I don't understand your answer.. there is no "driving axle". Power is spread equally between all wheels until one, anyone, loses traction
     
    Swine hauler, x1Heavy and pushbroom Thank this.
  8. lester

    lester Midwest's #1 Feed Hauler

    2,808
    7,451
    Jan 2, 2012
    NW, Iowa
    0
    I don't know anything about Freightliner suspension but I know one my low air Pete suspension the front and rear bags are not equal at ride height. Rear bags are extended further than front. Has to be to make the driveline angles right. Shouldn't be any check valves that I'm aware of either. All the bags should be plumbed together with leveling valve
     
    Oxbow and BoxCarKidd Thank this.
  9. Hero Biscuit vendor

    Hero Biscuit vendor Bobtail Member

    25
    39
    Jan 10, 2019
    0
    Follow the lines, maybe quick release valve is dickered. Could also have some protection valve to keep air tank from emptying if you blow a bag. Make sure there is only one leveling valve too. You could make a pressure gauge to temporarily T into the line and verify pressure is different at each bag. Just guessing don't take what I say as gospel :)
     
    Oxbow Thanks this.
  10. Hero Biscuit vendor

    Hero Biscuit vendor Bobtail Member

    25
    39
    Jan 10, 2019
    0
    More
    More I think of it, if you can phisically feel uneven pressure between the bags, I would think quick release valve. Your air dump is prob electronically controlled but it should still have a mechanical QR valve. If you have the leveling valve set wrong or it's broken, and it is overinflating the bags (jacked way up) it could also take weight off an axle but I think that would be the rear axle doing burnouts in that case.
     
  11. idigwesternstar

    idigwesternstar Bobtail Member

    13
    9
    Sep 14, 2019
    0
    Are you sure about that? I'm not super smart in that area, actually in any areas, but my understanding was that the back axle was the power axle, because the torque travels to the farthest point. If the pumpkin is closer to the left side, the axle is longer on the right side or vice versa. Therefore, the most torque when you're driving would be going to the right rear wheel, or vice versa. Or am i totally off my rocker? That's what I've understood mechanics to say.
     
  • Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.