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4x4 not engaging

Discussion in '1st Gen. Tacomas (1995-2004)' started by turtle142, Sep 8, 2021.

  1. Sep 8, 2021 at 2:38 PM
    #1
    turtle142

    turtle142 [OP] Active Member

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    Got a 1996 taco 2.7 manual transmission manual 4x4 shifter.

    When I shift into 4x4 the light will not come on and the front wheel wont engage.

    Think its something with the front diff, check the vacuum lines they seem fine.
    What else can u check before i tear the actuator off the diff?

    Is there a relay for the 4x4?
     
  2. Sep 8, 2021 at 2:59 PM
    #2
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Welcome to TacomaWorld
    If the air vent hose is off of the actuator moisture gets in and corrodes it.
    Check the 4wd position switch and connection on top of Tcase passenger side.
    There are 4wd selnoids in engine compartment that turn the vacuum on and a vacuum accumulator tank on drivers side wheel well.
     
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  3. Sep 8, 2021 at 3:18 PM
    #3
    turtle142

    turtle142 [OP] Active Member

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    I saw there is a hose that goes from the charcoal box down to the diff but it not connected to anything.

    The front drive shaft engeages so not sure if it be the sensor on the t case.

    Is there a sensor on the front diff, and if so is it the same kind?
     
  4. Sep 8, 2021 at 3:45 PM
    #4
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    No sensor on differential,
    The ADD Actuator has a switch which turns the green 4x4 dash light on when it fully engages the differential.
    Jshift engages the FDS
    4wd position switch sends signal to relay which switches vacuum on at ADD Actuator.
    UNLESS
    You have free wheeling front hubs (manual locking hubs), in this case you don't have ADD front differential.
    (Automatic Differential Disconnect)
     
  5. Sep 8, 2021 at 3:53 PM
    #5
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    @turtle142
    Does this hose have a breather vent on top? Little metal 1way valve cap.
    "I saw there is a hose that goes from the charcoal box down to the diff but it not connected to anything."

    Do you know the difference between a charcoal cannister and Vacuum Accumulator tank ?
     
  6. Sep 8, 2021 at 4:32 PM
    #6
    Junirol

    Junirol Well-Known Member

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    Hmm... I would check to see if vacuum is being applied to the ADD, VSV solenoids may not be working correctly or hoses might be disconnected or have holes. If you can't find anything wrong, I'd put the vehicle on jack stands and apply vacuum directly to the ADD actuator and see if the front wheel locks, if not it may be the actuator itself.
     
  7. Sep 8, 2021 at 5:04 PM
    #7
    turtle142

    turtle142 [OP] Active Member

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    Its automatic locking hubs, not manual, ill look for a breather tube on the top.

    If the 4wd position switch is bad whould that cause it from not locking ?

    Also i see the charcoal box but dont know what the vacumw acxumlater tank looks like.

    Where is the relay located that sends the signal to the actuator?
     
  8. Sep 8, 2021 at 5:40 PM
    #8
    turtle142

    turtle142 [OP] Active Member

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    What do the 2 electric wire go to on the front diff?
     
  9. Sep 8, 2021 at 5:42 PM
    #9
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Accumulator tank is in drivers side wheel well towards front. It's a small cylinder about the size of a long oil filter. 4wd vacuum switch for ADD is dependent on 4wd position switch, connection and wiring.
    Follow the vacuum hoses to find the relay/switch and vacuum tank.
     
    Last edited: Sep 8, 2021
  10. Sep 8, 2021 at 5:56 PM
    #10
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Transmission control module under passenger side kick panel. The wires turn the green 4wd light on via the module when vacuum has fully engaged ADD actuator and diff is locked in.
     
  11. Sep 8, 2021 at 5:58 PM
    #11
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Vacuum ADD has 2 wires
    Electric ADD has 6 pin harness plug.
     
  12. Sep 8, 2021 at 6:03 PM
    #12
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    @turtle142
    "Where is the relay located that sends the signal to the actuator?"
    Vacuum ADD actuator doesn't get electric signal.
    It's vacuum actuated.
     
  13. Sep 8, 2021 at 7:41 PM
    #13
    turtle142

    turtle142 [OP] Active Member

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    I should start by checking the switch on the transfer case and go from there?
     
  14. Sep 8, 2021 at 7:51 PM
    #14
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Easy enough with a multimeter.
    Unplug and test the switch side while Jshift in 4hi. You're looking for no continuity in 2wd,full continuity in 4wd.

    To test the ADD Actuator you'll need a hand vacuum pump. That's probably the culprit if the vent hose has been off for some time.
     
  15. Sep 14, 2021 at 7:26 PM
    #15
    turtle142

    turtle142 [OP] Active Member

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    Looks like there is a switch / sensor on the front diff, would it not engauge if The switch os broken?
     
  16. Sep 14, 2021 at 9:07 PM
    #16
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    You asked this in your #3 post.
    I answered in my #4 post
     
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  17. Sep 15, 2021 at 11:46 AM
    #17
    turtle142

    turtle142 [OP] Active Member

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    The solenoid is located on the front diff correct?
     
  18. Sep 15, 2021 at 11:54 AM
    #18
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    You have Vacuum ADD Actuator.
    The front differential is engaged and disengaged by Vacuum.
    No Selnoid on your front differential only electrical is a switch for green 4x4 light on dash cluster.
     
  19. Sep 15, 2021 at 12:18 PM
    #19
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Located under hood, drivers side on top of fender in the Rats nest of hose and wire.
    See post #2
     
  20. Sep 15, 2021 at 2:55 PM
    #20
    turtle142

    turtle142 [OP] Active Member

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    I take it this is theses are the silinoids. Is that the air vent on the corner or am I missing a hose?

    Also is there a way to test these silinoids? Ants fuses for them?

    Thank you, your help is much appreciated

    IMG_20210915_174044597.jpg
     

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