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Weak brakes on the drive axle

Discussion in 'Trucks [ Eighteen Wheelers ]' started by olpa77, Apr 26, 2012.

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  1. Apr 26, 2012 #1
    olpa77

    olpa77 Light Load Member

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    I have been having a problem with my drive axle brakes not working correctly. I have a 96 freightliner fld 120 without abs. It seems like my trailer and steer axle brakes are doing all the stopping. The drums on the trailer and steer axles are running hot while my drives will be just warm. Every thing is in adjustment. I have been in the shop 4 times and replaced many valves (foot, mv-3, and proportioning valve). The brake chambers were replaced a little over a year ago. "S"cam and bushings are good. Pads are about 60%. I am really stumped here, anyone have any ideas? :biggrin_25511:
     
    olpa77, Apr 26, 2012
    olpa77, Apr 26, 2012
    #1
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  3. Apr 27, 2012 #2
    bender

    bender Road Train Member

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    I had one doing this and the foot valve was leaking air, so it was a no brainer to replace it, but still had lack of stopping power from the drives. I then replaced the drive axle service relay and BINGO! Stopped like a Champ!

    You could check applied air pressure to your service brake chambers rather than just replacing the valve, but due to the price of a service relay and labor I'm not sure that would be cost effective.
     
    bender, Apr 27, 2012
    bender, Apr 27, 2012
    #2
  4. Apr 27, 2012 #3
    itchygomey

    itchygomey Bobtail Member

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    Try backing the steers and the trailer way off. Then apply about 15lbs. The only shoes working will be the drives. This will tell you if it's a problem applying pressure or if the shoes just aren't doing the job. I know it's a long shot, but ya never know. Hate to overlook the obvious!
     
    itchygomey, Apr 27, 2012
    itchygomey, Apr 27, 2012
    #3
    canadianrebel Thanks this.
  5. Apr 27, 2012 #4
    Pablo-UA

    Pablo-UA Road Train Member

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    do you have LSV? old trucks w/o ABS had LSV valves
     
    Pablo-UA, Apr 27, 2012
    Pablo-UA, Apr 27, 2012
    #4
    olpa77 Thanks this.
  7. Apr 27, 2012 #5
    olpa77

    olpa77 Light Load Member

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    Not sure if it has an LSV or not, but if older trucks had them I bet mine does too. Any idea where it would be located at? Freightliner told me there is a valve on it that cuts braking effort to the drives when bobtailing. They said when I push in the trailer brake valve on the dash the valve should then return normal braking effort to the drives. They replaced that and it did not correct the problem. Also the valve bender is talking about what does it control and where would it be located at?
    I have very little knowledge about the air brake system. I never knew there could be so many relays and valves. When it comes to the air brake system I always take it to a shop. However I have spent $1500 in the shop and the problem has yet to be corrected!
     
    olpa77, Apr 27, 2012
    olpa77, Apr 27, 2012
    #5
  8. Apr 27, 2012 #6
    bender

    bender Road Train Member

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    LSV or load sensing valve is the the one Freightliner is referring to. I don't know the location of that valve. The service relay should be on the frame rail back by the drive axles. The service relay valve sends air directly to the service side brake chambers.
     
    bender, Apr 27, 2012
    bender, Apr 27, 2012
    #6
  9. Apr 27, 2012 #7
    bender

    bender Road Train Member

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    Was the proportioning valve that was replaced at the front of the truck for the steering axle?
     
    bender, Apr 27, 2012
    bender, Apr 27, 2012
    #7
  10. Apr 27, 2012 #8
    olpa77

    olpa77 Light Load Member

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    The proportioning valve was right in front of the fifth wheel. It is the valve that freightliner replaced. It is also the valve they said controled the braking effort while bobtailng.
     
    olpa77, Apr 27, 2012
    olpa77, Apr 27, 2012
    #8
  11. Apr 27, 2012 #9
    bender

    bender Road Train Member

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    OK, that's what Pablo was calling the LSV. All you have left is the service relay valve, unless someone misadjusted your drive axle brakes.
     
    bender, Apr 27, 2012
    bender, Apr 27, 2012
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    olpa77 Thanks this.
  12. Apr 27, 2012 #10
    olpa77

    olpa77 Light Load Member

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    I'll recheck adjustment and try replacing that vavle and let ya know. Thanks.
     
    olpa77, Apr 27, 2012
    olpa77, Apr 27, 2012
    #10
    bender Thanks this.
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