88' freightliner 3406b jake doesnt engage & trac/trailer dash valve ????

Discussion in 'Freightliner Forum' started by flc120, Nov 12, 2014.

  1. flc120

    flc120 Heavy Load Member

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    well guys the truck is a mech b model 3406b cat gentleman claimed that it was working before but now its not working the truck does have jake brake on engine and switch on dash. before i start probing everyere do these trucks have a solenoid somewere that's controls this circuit somewhere? is it behind switches in dash?




    another issue truck has is the dash valve when pushed in and truck is bobtail leaks air from behind dash from what i think is valve supposedly the gentleman who owned it stated that when hooked up to a trailer and hoses connected that it wouldn't make noise at valve on dash? is this a faulty dash valve or should i look somewere else like one of the valves on chassis which goto trailer? its just annoying to hear the dam hissing all the time when driving bobtail.


    any help on this would be greatly appreciated.
     
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  3. baha

    baha Road Train Member

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    Jul 25, 2013
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    CK. for 12v at on/off switch over clutch pedal, that switch will stop jakes from working with clutch pressed in.
     
  4. wore out

    wore out Numbered Classic

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    There is also an on/off switch on back of the fuel pump thats bad to come unplugged.
     
    flc120 Thanks this.
  5. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
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    woreout the owner said something about this switch on back of pump. do you know what it looks like? unplugged or will i have to replace
     
  6. wore out

    wore out Numbered Classic

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    Its just a little 2 prong switch with the flat blade connectors usually. it should have power to one side then the ball in the switch completes the circuit to send power out to the other side. Its purpose is to activate the jakes only at an idle, if you have to replace it it will have to be adjusted but thats not hard. After starting it in the threads start the truck screw it in till it bumps the idle up then back it out till idles it back down. you just want it touching the rack is all
     
  7. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
    Miami,FL (yeah i know :( )
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    ok ive had two prior b model cats and they were 7fb's this one appears to be a 7xc? does this exist it looks to have a smaller turbo and really doesnt have that low to mid range kick the 7fb engines have. what gives i also noticed this engine has the pointy timing nose gear cover as the 7fbs have sorta of a shorter cover.
     
  8. wore out

    wore out Numbered Classic

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    CHASIN THE DEVIL'S HERD
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    It's just a newer design and dual scroll plungers in the pump.
     
  9. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
    Miami,FL (yeah i know :( )
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    does anyone know what my dash valve leak might be from?

    also WOREOUT I checked and theres a switch looking thing on the back of pump with two wires one coming out of each side with spade connectors both wires are connected to switch.i noticed there were 2 other switches on the clutch pedal mounted to the floor under the cab.
     
  10. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
    Miami,FL (yeah i know :( )
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    what would be a reason why im getting an air leak out of dash valve when not hooked up to.trailer or when valve is parked. but when i connect a trailer no more leak???
     
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