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Tractor drive brakes not grabing

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Canary379, Nov 27, 2013.

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  1. Nov 27, 2013 #1
    Canary379

    Canary379 Light Load Member

    64
    3
    Apr 13, 2012
    Illinois
    0
    Hello everyone, I have an issue with my tractor drive brakes not seaming to grab when I am braking. I drive an 2001 Pete 379 with a 24 ft dump trailer. When I am braking I can feel the steer grab and the trailer grab. I know know the drives are not grabbing because when they do which is not often I can really feel the difference and smooth stopping.

    does anyone know why this may be? Is there an equalizing valve somewhere in the system or maybe the tractor protection valve is too blam. Could it be the anti lock braking system and the service valve that mounts in between them?

    any help would be much appreciated.

    nick
     
    Canary379, Nov 27, 2013
    Canary379, Nov 27, 2013
    #1
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  3. Nov 27, 2013 #2
    dude6710

    dude6710 Road Train Member

    2,162
    622
    Mar 26, 2010
    MN
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    Slam on the brakes very hard going 40+mph

    auto slack adjusters should re adjust with 90 +psi applied to the brakes.
     
    dude6710, Nov 27, 2013
    dude6710, Nov 27, 2013
    #2
  4. Nov 27, 2013 #3
    luvtotruck

    luvtotruck Road Train Member

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    Jul 30, 2013
    Phoenix Arizona
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    I was thinking they were not adjusted correctly either! I'm sure slamming on them will get them adjusted!
     
    luvtotruck, Nov 27, 2013
    luvtotruck, Nov 27, 2013
    #3
  5. Nov 28, 2013 #4
    123456

    123456 Road Train Member

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    Oct 22, 2010
    32179
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    Just as easy to slam them on at 0 mph,

    isn't it ?
     
    123456, Nov 28, 2013
    123456, Nov 28, 2013
    #4
  7. Nov 28, 2013 #5
    Les2

    Les2 Road Train Member

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    Jul 25, 2008
    kicked back in my lazyboy...
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    Shouldn't have to slam them on at all really. Once they go so far something in the slack should click over and thats how they adjust. I've never applied 90psi to the brake pedal and there really should never be a reason to unless its an emergency stop.

    Push the button in and have someone push the brake pedal while you watch the slack adjusters to make sure they are even moving. If they are try adjusting them manually and see if it makes a difference in stopping. If it doesn't your brakes/drums could be glazed over. If you have no movement you have a valve issue.
     
    Les2, Nov 28, 2013
    Les2, Nov 28, 2013
    #5
    truckman29801 and rollin coal Thank this.
  8. Nov 28, 2013 #6
    dude6710

    dude6710 Road Train Member

    2,162
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    Mar 26, 2010
    MN
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    Yes but it could be funny to watch at 40
     
    dude6710, Nov 28, 2013
    dude6710, Nov 28, 2013
    #6
    Sublime and 123456 Thank this.
  9. Nov 28, 2013 #7
    truckman29801

    truckman29801 Medium Load Member

    469
    109
    Mar 10, 2013
    SC
    0
    Did you get out and adjust them? ABS shouldnt be the problem because if it senses wheel lock up it diverts air out of purge valves to release pressure on the chambers, which you would hear the valves spitting out air. anyways i doubt its that. I would say the best bet is to unhook the trailer, crawl under with the wheels blocked and check the adjustment on the slack adjusters. Ive never seen an Automatic slack adjuster do its full job. when is the last time you had the rear brakes done?
     
    truckman29801, Nov 28, 2013
    truckman29801, Nov 28, 2013
    #7
  10. Nov 28, 2013 #8
    catmechanic07

    catmechanic07 Bobtail Member

    30
    20
    Dec 10, 2010
    Roanoke, VA
    0
    If there Is no movement, you could have a bad valve but you can also have a seized "S" cam. The S cams that don't grease are great for doing this. Either they don't move or move very little.

    Brakes could be out of adjustment, glazed or possibly ready to cam over.

    Valves USUALLY leak air when there is a problem. You may even have a bad chamber or chambers
     
    catmechanic07, Nov 28, 2013
    catmechanic07, Nov 28, 2013
    #8
  11. Nov 29, 2013 #9
    Pablo-UA

    Pablo-UA Road Train Member

    7,604
    1,640
    Oct 11, 2010
    Borispol, Ukraine
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    is there LSV valve?
     
    Pablo-UA, Nov 29, 2013
    Pablo-UA, Nov 29, 2013
    #9
  12. Dec 1, 2013 #10
    Canary379

    Canary379 Light Load Member

    64
    3
    Apr 13, 2012
    Illinois
    0
    Thanks for your input guys.... The brakes them selves are good. Lots of pad on them. I had my dad under the truck while I depressed the brakes and he said all the brakes are engaging. The issue I am having is that there is no stopping pressure applied to them. I am replacing the relay valve that is attached to the ABS valves and seeing if that helps. I had a cracked head a little while back and there was a grayish sludge that was in the air lines so I think that maybe some of that made its way to the valves and is causing a pressure issue when applied. Just one possibility I thought of.
     
    Canary379, Dec 1, 2013
    Canary379, Dec 1, 2013
    #10
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