Weird ABS/brake acting.

Discussion in 'Volvo Forum' started by Snailexpress, Jul 21, 2020.

  1. Snailexpress

    Snailexpress Road Train Member

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    Truck brakes are weak with trailer attached. Brake pads looks like new for four years and rusty drums, no wear.
    Bobtail braking seems not bad.
    When parked on hill with truck only parking brake set and turn key on ABS release parking brake for split second and rig rolling little bit.
    No ABS codes, sensors calibrated, replaced treadle valve, dash valves, tractor protection valve.
    Any suggestions? My head spinning.
     
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  3. uncleal13

    uncleal13 Road Train Member

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    Broken parking spring in brake pots?
     
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  4. Snailexpress

    Snailexpress Road Train Member

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    Parking brakes are good. Few DOT inspections passed with no citation.
    Acting is intermittent, not every key on.
     
  5. ryantyre

    ryantyre Bobtail Member

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    Relay valve? (ABS valves attached to it)
     
  6. nasriza

    nasriza Road Train Member

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    Need to replace chamber springs inside broke or weak replace parking chamber with long strokes and you will be good or make sure quick release valve dumping air out right away.
     
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  7. Snailexpress

    Snailexpress Road Train Member

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    Some updates. Not fixed yet but what i have figure out the problem is in brake anti compounding. Rear relay valve ATR-6 located under fifth wheel connected with quick release valve thru signal line.
    When ignition is ON ABS module start click click chaff and actuate solenoid on the relay valve. Relay sends air pressure to QR valve to release parking brake. It suppose to apply service brake equally to pressure in parking release to prevent double force to the drums. Spring + service force. It's probably was the cause of why 3 air chamber brackets got broke. Spent couple hours on the phone with Bendix technical support. They recommended to replace relay valve first.
    Waiting for parts.
    Stay tuned.
     
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  8. nasriza

    nasriza Road Train Member

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    Can you please post. Pic of quick release valve there is a fitting on top that can malfunction.
     
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  9. Snailexpress

    Snailexpress Road Train Member

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    I'll try to shoot video tomorrow.
     
  10. Snailexpress

    Snailexpress Road Train Member

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    OK got video today to better explanation what is wrong.
    Part 1 - Turned ignition on and run to back air chambers. You can see how parking brake start releasing.
    Part 2 The valve to which air cambers parking hoses are connected. It's something like anti compound valve or double check valve. Two small tubes on the top, green connected to service brake relay valve and red connected to the dash valve. Air pressure from ether tube will release parking brake.
    Part 3 If I pull green tube off the valve parking brake doesn't release but air blowing out.
    If I release parking brake from dash valve no air coming from green tube or valve and brake released.


     
  11. AModelCat

    AModelCat Road Train Member

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    That's sketchy!

    What supplies air to the line you removed?



    Gotta say videos make it so much easier to understand what's actually going on.
     
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