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locking torque converter

Discussion in 'The Garage' started by x_hvy_chvy_x, Apr 26, 2005.

  1. x_hvy_chvy_x

    x_hvy_chvy_x Newbie

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    hi guys,well to get to the point we have the computer all unhooked in my 88 blazer we changed it over to carb and now my torque converter don't lock.what can i do to make it work like it should with out all the computer stuff being hooked up.oh i have the 700R tranny.thanks
     
  2. loafer

    loafer 1/2 ton status

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    The ECU controls TC lockup. You can wire up a manual switch or you can set it up to work like the carbed trucks which use the following:
    -VSS from a carbed truck (prevents lockup under 35MPH)
    -low vacuum switch (unlockes converter under high load)
    -tie into your existing brake switch

    All these need to be wired in series, so when all switches are closed you get +12V to the TCC solenoid.

    Bowtied Overdrives also sells a kit:
    http://www.bowtieoverdrives.com/catalog/catalog.php?Action=GETSUBCAT&CATID=O

    Why did you ditch the EFI? The factory TBI is simple, reliable and more fuel efficient.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Apparently VSS isn't used for lockup, it's solely a function of the vacuum/brake switch.

    I thought it was previously as well, but reviewing the earlier wiring diagrams, I couldn't find anything tying VSS to TCC.

    If you had a 700R4 truck without cruise, there'd be no cruise computer, (which DOES use VSS of course) and as far as I know/have ever seen, there is no standalone TCC controller, which there would need to be for VSS to work with the TCC.
     
  4. TorkDSR

    TorkDSR 1/2 ton status

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    there are simple kits to make it manual/automatic from summit/jegs. but i think the nicest thing is a full manual lockup with an old headlight switch on the floor where the clutch pedal would be
     
  5. x_hvy_chvy_x

    x_hvy_chvy_x Newbie

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    thanks guys. could ya tell me what wires i would use fer my choke?
     
  6. loafer

    loafer 1/2 ton status

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    I have an 86 k5 with cruise, and it uses VSS for lockup. It locks up in 3rd over 35MPH, which is a benefit IMO. Maybe non-cruise trucks only locked up in forth, similar to the Bowtie Overdrive kit.

    In stock configuration the low vac. switch only unlocked the clutch in 3rd. I added a second switch to mine to unlock in 4th as well (similar to the ECU controled TCC in the factory TBI trucks) when I converted to EFI.
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    You sure that isn't a function of the pressure switches?

    If it isn't, where is the controller for TCC with VSS input?
     
  8. x_hvy_chvy_x

    x_hvy_chvy_x Newbie

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    ok guys u got me lost i don't know what TCC AND VSS is at all this is all new to me
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    TCC=Torque Converter Clutch.

    VSS=Vehicle Speed Sensor. In your case it's read off the speedometer cable to tell electrical components how fast the vehicle is traveling.
     
  10. loafer

    loafer 1/2 ton status

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    The pressure switch is hooked directly to full manifold vacuum, so under high vacuum (light engine load) the swich is closed allowing lockup. When I drive 25-30MPH in 3rd gear under light engine load the TCC will not lockup and the switch is closed, but it will lockup as soon as I pass 35MPH in 3rd gear...so I'm assuming that it must be the VSS.

    I don't know where the controller is. I'll have to poke around next time I pull the dash out.

    My previous 3 trucks were factory EFI with computer controlled lockup, so I'm still learning about this system myself.

    Another curious thing I found is that the AIR circuit (I no longer run this), shares a common yellow wire with the TCC lockup circuit, which is the same wire that goes to the brake swicth to unlock the TCC. Why would the AIR be tied to the brake switch? It looks like the AIR solenoid would de-energize whenever the brake is applied...Must be an emissions thing.

    I should also add that my truck had the California emissions package, so it might be set up different then many.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    I was going to ask if it had CCC. I am 99% positive the CCC setups (CA on our trucks) control TCC through the ECM, which WILL have VSS input.

    All GM cars from 1981-1990 carbed are CCC and control lockup through the ECM, so speed input for lockup was the norm. Now with the truck CCC setups (even more pieced together than CCC on cars) anythings possible, but for monetary purposes, it wouldn't make sense not to keep it the same on trucks.

    My '83's lockup was very speed consistent too, (which I why I assumed all were VSS controlled) but only as long as I was in the same conditions of course, such as flat ground, unloaded, etc.

    I've never really paid attention, but as much as I used to go to the wrecking yard, I'm sorry I never proved this...if you ever see a 700R4 truck without VSS, it would solve the question.

    I'm not 100% positive, I've seen nothing that PROVES VSS wasn't used for lockup in trucks, but I've never seen anything that proves it was. (wiring manual or visual proof) Heck, for a long time on this board, it was argued that manual transmission TBI trucks didn't use VSS, eventually this was disproven, but it took awhile.
     

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