Brake problem with trailer attached.

Discussion in 'Volvo Forum' started by Snailexpress, Apr 6, 2020.

  1. Snailexpress

    Snailexpress Road Train Member

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    Something is wrong with my truck brakes when trailer is attached. If I apply brakes hard the trailer brake locks until trailer ABS release. At the time trailer ABS release there is no brake at all or very little on the truck. Trailer swap doesn't helps.
    Bobtail brakes is OK. Passed 2 level 1 inspection all good for slack adjusters or shoes. Brake shoes have almost no wear in 3 years. Weird!
    Changed treadle valve, dashboard valve, tractor protection valve, nothing helps.
    ACom diagnostic all test and calibration done, nothing wrong.
    Any ideas where to look?
     
    truckdriver31 Thanks this.
  2. truckdriver31

    truckdriver31 Road Train Member

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    rubber or plastic airlines. check the blue air line. you run in the bottom all the time. little bugs can get into air hook ups.
     
    Snailexpress Thanks this.
  3. baha

    baha Road Train Member

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    Just because you put put replacement parts on the truck does not mean you they were any good, many brake parts are rebuilt and do not work right out of box, that bobtail valve puts alot of air to FT. brakes and alot less to drive axles, when red button is out, you need to look at the crack pressure that should be stamped on the steel tab on top of drive axles brake service valves, if crack press. on valves are not matched you may not be getting any air to drive wheels till you mash the hell out of them, getting a air gauge with fitting on both sides so you can put it on all of lines on side of air brake valves that lead to brake chambers, then ck if air press. is the same as the gage on dash if truck has one if not put one in line and hang it in dash so you can ck. if all lines are getting the same press with red button pushed in?
     
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  4. Snailexpress

    Snailexpress Road Train Member

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    So far ABS system is under suspicious. ABS module or modulators.
     
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