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Lock-up converter troubleshooting

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Sidepipes, Jan 12, 2003.

  1. Sidepipes

    Sidepipes 1/2 ton status

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    Heres the story. 86 Jimmy, 89 drivetrain( 350, 700r4, 241) including the computer and harness.

    My convertor is not locking up... ever. The Haynes manual is no help whats so ever.

    From what I've read, the converter is supposed to lock up at speeds of 25MPH+ and in third and fourth gear. What are the other things that must happen for it to lock up? Are there any? I personally though it was controlled by the computer( ie no vacuum switch) but maybe I'm wrong.

    Anyways, there are 3 wires in the 4 pin connection to the tranny. Does anybody know what each one is for? I believe mine are pink, blue and green. I would assume that pink is power to the switch and the others are the ground wire( probably green) and the signal wire. am I right?

    Once I figure this out I'll hook a multimeter up to the hookup to see if everything is right, then take it for a drive to see if the lockup signal is there.

    If the signal is there what else is wrong?

    TIA for all the help guys.
     
  2. 95 Silverado

    95 Silverado 1/2 ton status

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    there are some variations in the way these transmissions are wired internally over the years, but I think the external plug is pretty consistent. One wire will be the power wire supplying voltage to the convertor lock-up circuit, this voltage runs through the circuit breaker or fuse and the brake switch,(and vacuum switch on earlier models) if either one is open you will get no lock-up voltage. the second wire will be the ground side of the lock-up solenoid which goes to the ECM, the ecm controls lock-up by switching the ground side of the solenoid circuit. the third wire is a signal wire from a pressure switch in the valve body, the switch closes, making a path to ground when the transmission shifts into fourth gear, this wire also goes to the ecm, the ecm uses this signal to know when the transmission is in overdrive.
     
  3. Sidepipes

    Sidepipes 1/2 ton status

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    Thanks for the help. I'll check for voltage at the wires.....any idea which wire is for lockup and which is for the overdrive sensor? I guess if I 12 volts at two connections everything is good right?

    I 'll check this stuff out and then check for continuity in the wires. If both of these pan out, Anybody else have ideas?

    Its not a really big deal as it is winter so temps aren't much of a bother( after the rad change I can't get the engine warmed up enough so the tranny cooler is definitely capable of containing the heat)

    Its the 10mpg that I'm getting... I'd like to get it a little better. /forums/images/graemlins/1zhelp.gif
     
  4. Kyle89K5

    Kyle89K5 1/2 ton status

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    I'm assuming you've chased out the wires to look for any bare spots or breaks? Mine broke back up towards the bellhousing and was a bear to find. I little solder work and it's working fine. If I get a chance, I'll slip down and tell you which one on my 89 broke. I.E. color.

    KP
     
  5. Sidepipes

    Sidepipes 1/2 ton status

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    I've looked at the wires up to the point I can get to then. they are in great condition up until it gets to the top of the bellhousing and goes in another harness. The next step is to to check for voltage and then contintuity

    I'm on Bowtie Overdrives website right now reading up on it, hopefully they'll have the right info.
     
  6. Blue85

    Blue85 Troll Premium Member

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    Here's more stuff for you to check. With the key in "run", you should get 12V at one of the pins on the tranny connector. If not, check fuses and the the brake switch. If you do have 12V, try grounding each of the other two pins, one at a time. One of them is the low side of the solenoid. You should hear a click from inside the tranny when it is grounded. The other pin is a feedback switch and will just be open circuit while you aren't driving, so it won't hurt anything.

    The whole engine and tranny harness was swapped over from the newer truck, right?

    No vacuum switch on the ECM trucks. The ECM has full control over lock up, except that the brake pedal can overide it.
     
  7. Kyle89K5

    Kyle89K5 1/2 ton status

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    If I'm looking at mine right (tough to do in the parking lot in decent clothes) the green wire was the one that was broken on my truck causing no lockup. Where you lost the ability to look any further on yours was right about where mine was broken.

    Good luck.
     
  8. Sidepipes

    Sidepipes 1/2 ton status

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    Kyle thanks for getting under the truck... I understand the decent clothes thing..... I had to help someone roll up a 4" temporary air compressor line today... lets just say my dress pants and gold shirt are covered in salt/mud same with my jacket.

    Blue85, thanks for the troubleshooting lesson, it will help me greatly!

    I found some interesting wiring diagrams at bowtie overdrives. There is one system using a cruise control brake switch that will lock up the converter anytime its in 4th gear. Plus you can add a manual switch to lockup in other gears.... plus if you want you can hook the switch prior to the brake switch so you could use it for compression braking when needed. Their website is 700r4.com if you want to look at them.

    Now if it was so cold and it wasn't snowing, I could figure this thing out!
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    You can ground two pins on the ALDL connector and force lockup if its got power, can't remember the pins, might be A and F. Just need a paperclip.

    You can find that info real easy online.
     
  10. Sidepipes

    Sidepipes 1/2 ton status

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    Dorian, thanks, thats much easier. In fact I have a jumper wire sitting in the console for checking codes.
     
  11. R72K5

    R72K5 Banned

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    i have an 83 vehicle with 700r4 and issues with it locking up all the time and i hate it, it does lock in after second-third shift, i have been trying for a long time to find out if theres anything wrong with unplugging the lockup connector on trans case
     
  12. Sidepipes

    Sidepipes 1/2 ton status

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    go to www.700r4.com they have a bunch of diagrams on how to hook up the lock up converter from manual to automatic lockups. read what they have to say about using the lock up, it makes a lot of sense. I don't see any problems with unhooking the switch but why not fix the problem. It'll give you better economy and we need all we can get with these trucks plus better engine and tranny longevity!
    See ya later, 9 month olds, a computer keyboards don't mix too well..... it took me 5 minutes to type this drival because she kept on smashing the keyboards with her hand. now she's crying. see ya!
     
  13. HarryH3

    HarryH3 1 ton status Author

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    I'm pretty sure that an '86 should have a vacuum switch mounted on the firewall, passenger side, that is part of the lockup circuit. I think there are a pair of green wires going to it, along with a vacuum hose. If the vacuum hose is disconnected, then the lockup won't work. When vacuum is high (part throttle cruise) the switch is closed. When you mash the loud pedal, vacuum drops and the switch opens, telling the converter to unlock. /forums/images/graemlins/cool.gif
     
  14. Sidepipes

    Sidepipes 1/2 ton status

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    Harry, the complete drivetrain is out of an 89- engine, tranny, trasnfercase, computer , wiring harness everything. They guy who did it did it right..... almost

    I jumpered the ALDL to activate the solenoid and got nothing. I'll check for Voltage at the correct terminal and then look for a bad wire. Its probably a bad ground of some sorts, just gotta find it...... that shouldn't be too hard /forums/images/graemlins/rolleyes.gif
     
  15. HarryH3

    HarryH3 1 ton status Author

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    Ah, I missed the part about the swap. /forums/images/graemlins/blush.gif You'll probably need a wiring diagram to totally sort it out. You'll probably find that something isn't hooked up quite right. It may be something as simple as the brake light switch wiring. An '89 would have tied the lockup circuit into that to tell the tranny when to unlock the converter. If that isn't hooked up right, then the trans thinks that the brakes are being applied and it will never lock up the converter.
     

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