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No TCC lockup when trans is warm

Discussion in 'The Garage' started by zcarczar, Oct 23, 2003.

  1. zcarczar

    zcarczar 1/2 ton status

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    My tranny wont lock up anymore when it gets up to operating temperature. I have a manual lock up switch and I can engage it and nothing happens, and yes the speedo and VSS work because the trans will lockup before it gets above 125*. Anybody have any ideas? /forums/images/graemlins/1zhelp.gif
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

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    What year vehicle is this? IIRC, my old 700R4 would NOT lock up until it was warmed up. How is yours wired?
     
  3. zcarczar

    zcarczar 1/2 ton status

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    Its an 89 700R4. Wiring is stock except for the added lockup switch that just grounds out the ALDL lead for the TCC. I got the plans for the switch off of thirdgen.org.
     
  4. zcarczar

    zcarczar 1/2 ton status

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    /forums/images/graemlins/1zhelp.gif
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Only suggestion/thought I have is that the TCC solenoid is shot. If you can't FORCE it to lock up in 3rd or 4th, but it does when cold, you can rule out the clutch itself I figure.

    I don't know how the pressure switches interact with the lockup...I *assume* when wired up with a manual switch, the pressure switches (whatever is in the tranny) are bypassed when that is engaged.

    IIRC, that's what happens when you ground the correct two pins on the ALDL connector...the TCC solenoid is FORCED to lock.

    Solenoid essentially controls a plastic ball that acts as a check valve, with thicker fluid, (cold) perhaps it doesn't leak, and when it warms up and the fluid thins out, it does? Either that or an eletrical problem that is temp related, which the solenoid would be suspect of.
     
  6. zcarczar

    zcarczar 1/2 ton status

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    I initially thought it was a line pressure problem because the tranny would lock it self up with more throttle input while the manual lockup was on. But when i would back off the throttle say when I reached cruising speed the tranny would unlock itself until i reapplied the more throttle. But lately it wont even lock itself up when warm, until today when I was driving home from class the TCC was locking up but it wasn't locking up very solid like it used to. This also makes me want to think that the TC is burnt up and when more torque is applied to it it just slips into the unlocked mode.
     
  7. BobK

    BobK 1/2 ton status

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    My 700 did that.
    It would lockup when cold but once warm it wouldn't.
    Turned out to be my T/C.
    I replaced it and all is well again.
     

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