Finally figured out what’s reducing my mpg and causing my rear axle to warm up. Need advice

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by LoneRanger, Nov 25, 2021.

  1. LoneRanger

    LoneRanger Road Train Member

    Jun 3, 2018
    2013 Cascadia DD 15 on guard system

    2 weeks ago I realized a drag on my truck in neutral, even when downhill, I checked the front hubs although they were low on oil it wasn’t getting hot. One rear axle was getting warmer the the others. I checked the rear end oil to see if it’s low and brake clearance. All was well. Issue stopped after topping off the front hubs, causing me to believe maybe I Was low on oil.


    Today it started again and I was slowing down on down hills. I stopped checked hubs oil level is fine, rear axle getting warm. Fine seems as if I need to open the rear up. I started driving again and the issue wasn’t there no drag nothing.


    my auto brake kicked in because of a 4 wheeler. The drag on the truck came back, so I stopped again set the brakes and releases it after 5 min. Problems gone. Then I recreated the condition by getting close to a truck for the auto brake to kick in. I was successful.

    some how when my auto brake kicks in, seems as if one side does not fully release.

    this happened after adjusting the brakes.

    what components in the onguard system or braking system can cause this ?

    Please help me avoid the stealership and shady mechanics.
    blairandgretchen and BoxCarKidd Thank this.
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  3. flood

    flood Road Train Member

    Dec 25, 2010
    It sounds like It's in the abs circuit... on guard used the abs for braking...

    Check by turning on the truck (not starting) and listening to the abs cycling thru the self test.. when standing next to the truck I can hear it go around and air puff each brake 2x. If 1 or 2 don't do it or don't sound right check the valve for that wheel. could be blocked and not letting air out or the valve may be sticking and SLOWLY letting the air out
    Last edited: Nov 25, 2021
  4. AModelCat

    AModelCat Road Train Member

    Jul 7, 2015
    Sounds like maybe the exhaust port on a valve is sticking?
  5. Ross_Tech

    Ross_Tech Light Load Member

    Aug 31, 2021
    I would start with checking the rear modulator valves. I'm not sure about your exact set up, but most of them share the quick release exhaust port with the normal service brakes. It sounds like a modulator valve may be hanging open. You can check this by pulling off the air lines at the valve, and turning the ignition on to cycle("chuff test") the valves. If one port is leaking, after the chuff test, that's your culprit. It may have been a problem before you adjusted the brakes, but if the adjustment clearance got smaller, it may just now be apparent. Also, if the slack adjusters are working properly, the brakes shouldn't need adjustment unless a component is removed or replaced during service. So if you're going out of adjustment, you have an issue with the slack adjusters, or cams/rollers/etc.
    black_dog106, LoneRanger and Magoo1968 Thank this.
  6. Inderjit

    Inderjit Medium Load Member

    Sep 17, 2017
    I did a little research as I have no experience with the On-Guard system.
    The ABS modulator valves only operate when the ECU needs to control
    pressure to individual brakes. All trucks may not be set up the same but
    it looks like when the On-Guard system applies the brakes it does so with
    the traction control relay valve. The Traction control relay valve looks like a
    Bendix R-12 but it has a solenoid on top of it that is used by the traction
    control system and the On-Guard system to apply the brakes.
    Search the internet for: Bendix K070955 ATR-6 Traction Relay Valve.
    I would start with this valve, the valve the solenoid controls may not be
    closing when the power is switched off.
    Here is a link to Bendix's spec sheet on the valve:
    LoneRanger and Magoo1968 Thank this.
  7. Inderjit

    Inderjit Medium Load Member

    Sep 17, 2017
    There should also be a solenoid controlled valve that applies the trailer brakes
    located somewhere on the truck. Could the trailer brakes be the problem and
    not the truck brakes?
  8. LoneRanger

    LoneRanger Road Train Member

    Jun 3, 2018
    So close to a month later, here’s an update.

    problem persists but it’s gotten better.

    adjusted Jakes, brakes have been adjusted again this time off the ground so I can see if the wheel spins, front bearings done, rear brake replaced on one side, hardware replaced on other side as it wasn’t sitting correctly in the drum, and 2 regens done back to back

    as the issue has slowly gone away, I’m going to test and see if the on guard activates the brakes and comes back. If it does then that could be where the problem is.

    My DPF and one box are on schedule next month to be repaired not replaced and at that time I’ll have them clean the DPF filter to make sure all is well.

    I’ll keep you guys updated but as of now I’m feeling better as I don’t have any issues with the engine or Turbo as it was checked by an experienced mechanic.
    Last edited: Dec 22, 2021
    lwlevens and Pamela1990 Thank this.
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