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TCC lockup wires on 700R4, how many are there?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by PetaKane, Aug 11, 2002.

  1. PetaKane

    PetaKane 1/2 ton status

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    Anybody know what color and how many there are on an 87? I heard that they need to be hooked up in order for the tranny to operate best. I've gone from TBI to carb and this is another one of those headaches I've come across. Do they just need power and ground? Or will I have to put a toggle switch somewhere?
     
  2. ftn96

    ftn96 1/2 ton status

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    The plug has 3 wires. Power, ground and switch leg. Cant remember the colors. But you will need to have some way to control the lock up of the TC. If not you will burn up that tranny. You can get a univeral lock up kit for relatively cheap from TCI, B&M and companies alike. Or you can do the toggle switch. But you gotta make sure the lock up circuit runs (the switch leg part of it) to something that will unlock it when you con to a stop or it will stall the motor. Ask Blue85. He's the 700 wiring man.
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    You also must not forget about the TV cable. I think it is edlebrock who sells the speacial bracket for the TV cable when using a carb. If you don't hook up the cable the tranny won't shift correctly and you will toast your tranny
     
  4. PetaKane

    PetaKane 1/2 ton status

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    I've got the bracket for the kickdown cable, now I've got to figure how to hook the wires up so it will function the same as before.
     
  5. wrathORC

    wrathORC 1/2 ton status

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    Don't you have the vacuum switch from the donor vehicle?
     
  6. PetaKane

    PetaKane 1/2 ton status

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    I'm not exactly sure. Where is the vacuum switch normally located?
     
  7. wrathORC

    wrathORC 1/2 ton status

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    One of the two switches up above the air cleaner on the firewall/bulkhead/whateveryouwanttocallit.

    I can't remember which one is which because I did some serious re-routing under the hood and I'm kind of sleepy right now. You can't see the second one but the one next to my fuel pump you can see.

    I actually could have used the picture upload feature this time..

    [​IMG]

    If you could, would you let me know when you've seen the picture so I can get it off my website? I don't like having pictures up there I don't need because it makes archiving take longer.

    If you haven't figured it out by tomorrow afternoon let me know and I'll go crawl under the hood of my truck.
     
  8. PetaKane

    PetaKane 1/2 ton status

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    Okay, I really appreciate that. I've saved the picture so you can take it off. Thanks again though. Okay lemme see if I can get this straight. The three wires from the transmission go to that switch? And from there they go into the cab, right?
     
  9. wrathORC

    wrathORC 1/2 ton status

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    I don't know how many come from the transmission for sure. I believe I have three. The last time I looked was in March.

    At the vacuum switch is a blue wire and a blue wire with a black tracer. Going in to the cab is the blue/black, a green wire, and a light blue wire.

    I don't know what comes to the switch. It's raining now and I'm out of batteries for the camera.

    I took a couple more pictures before I ran out of batteries (I planned on splitting the looms and showing you the wires).


    In this one I'm holding on to the vacuum line.
    http://www.wrath.com/projects/vehicles/images/84k10/vacuumswitch.jpg

    The three wires going in to the cab.
    http://www.wrath.com/projects/vehicles/images/84k10/harnessgoingintotruck.jpg
     
  10. Blue85

    Blue85 Troll Premium Member

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    In the picture above the switch on the left is the "tip in" switch for the ESC. You don't need it unless you are using ESC with your HEI. The switch on the right is used for TCC lockup. It receives timed vacuum to ensure that the converter doesn't lock at idle or when your foot is in it, only for cruising.

    PetaKane,
    You'll have to do a little work to get lockup to work right when putting a carb on a TBI truck. I think that the ECM controlled TCC lockup in '87. Please identify for us how many wires are coming out of your tranny, as it varied by year and equipment. On the mid-80's carb trucks, the three wires were as follows:
    -constant hot, switched only by the brake pedal switch. This let the trans lock itself in 4th.
    -switched hot, through the vacuum switch, for controlled lockups in gears below 4th.
    -lockup output - controlls an electric vacuum switch for EGR that works only when the converter is locked. You probably don't have this wire and probably don't need this switch. In the carb trucks, it was mounted on top of the passenger-side valve cover, just in front of the transmission fill-tube.

    I don't think that you have the extra brake pedal switch in '87, either. If you can get if from the donor truck, do it. It is the switch on the left when you are looking at both of the switches connected to the brake pedal. If you can't get it, your existing brake switch should be OK, but you will have to add a relay to convert from normally open to normally closed.

    I think you have two options: pseudo-factory style lockup control or an aftermarket "universal" kit. Your valve body doesn't have the lockup control valve (the cavity is filled with a plug), so you can't have it exactly like factory carb, but it can be OK. The primary purpose of this valve was to use TV pressure to unlock the converter when the throttle was opened, which is a good thing. Without it, the vacuum switch probably won't unlock until you get close to WOT, so you will have to depend on a downshift to 3rd to unlock the clutch. I think you will need a pressure switch to thread into the 4th pressure test port. Then you can use the vacuum and brake switches to lock up the converter only when you are in 4th, cruising and not on the brake. The aftermarket kits use a speed controller.

    Try to give us some indication of which route you would like to take and then I can give more details. My opinion is that the factory controls are a lot better than the aftermarket kits, but a TBI trans can't have all of the factory controls (as I discussed above) without swapping the valve body.
     

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