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700 convertors- lockup or not?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Sidepipes, Dec 12, 2002.

  1. Sidepipes

    Sidepipes 1/2 ton status

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    Are all 700r4 torque convertors lockup units or not? I have an 89 drive train in my 86 whcih I just got. I don't think the lockup is working( if it has one) I had a 90 z-71 with the same drivetrain and when it locked up, you knew it had.

    If it doesn't lockup how bad is it for the tranny? or is it bad?
     
  2. Thunder

    Thunder 3/4 ton status

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    The 89 700r4 is a lockup type (unless someone installed an aftermarket non locking TC in it).
    In my opinion you should be using the lock up. When the convertor is not locked there is slippage in it. This generates unnessary heat. Heat is bad news for 700r4s.
    Non lockup convertors work ok in light street or race cars or maby a mud bogger or hill climber where you need the RPMs. But in a big heavy truck for normal use and wheeling i think the lock up is better. It helps keep the heat down at highway speeds and will help get better gas milage.

    Heres some more info on the subject and where you can buy a lockup kit.700r4.com
     
  3. Blue85

    Blue85 Troll Premium Member

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    Yes, all 700's came with lockup. Without it 4th gear can get the transmission really toasty. The lockup converters are not expensive, so I see no reason to ever swap in a non-lockup. You can always disable the locking function electrically without much work at all.

    If yours isn't working, chaces are it is an electrical problem. The lockup function worked differently in 89 and 86. The 89 used the ECM to control lockup, while the 86 used a combination of engine vacuum and hydraulic pressures to decide when to lock.

    You need to the lockup. To test whether or not it works, cruise in overdrive and gently touch the brake pedal without letting off the gas. This should raise the egine rpm slightly (as the converter unlocks). You can also set the cruise control and see if the rpm changes as you go up and down hills. If the lockup works, it won't change.

    To fix it, you've got to wire in your 89' tranny like the 86 was. OR get a pressure switch and thread it into the 4th pressure port on the side of the tranny. Then wire 12V through it to the lockup solenoid.
     
  4. Sidepipes

    Sidepipes 1/2 ton status

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    Thanks for the help guys. I'll start looking at it tomorrow.
    The guy who swapped the engine and tranny in said he pulled the whole harness from the 89 and put it in too, so I'm hoping its an electrical connection gone bad.
     
  5. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    If you start to pull a hill and the lock-up doesn't disengage you have problems my friend. A lock-up convertor should disengage when you start to pull a hill of moderate grade, and if the hill is large enough the tranny should even downshift into 3rd gear.
     
  6. Blue85

    Blue85 Troll Premium Member

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    Really, it should just downshift. If you pull a long grade unlocked at high speed you have lots of heat coming out of the torque converter. 700's are almost always locked in 4th gear, except for when they are shifting. Especially ones with aftermarket speed sensors or lock-up kits. You can't get them to unlock in 4th without touching the brake pedal. This is fine. If the engine has to work that hard, 3rd gear is ready and waiting.

    What I am saying is that as you go up and down soft grades with the cruise set, your speed is constant, but the engine load is not. If your converter is unlocked, then it's slip is proportional to the torque through it. So your rpms will be higher as you go up than when you go down. If the converter is locked, the egine rpm is the same all the time, as long as the cruise control keeps the speed constant.
     
  7. workingman

    workingman Registered Member

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    See here for a lot of 700r4 tips

    http://www.transmissioncenter.net/700R4.htm

    Heres an excerpt:

    "If you have a 1982, 1983 or early 1984 transmission (27 spline input shaft)
    it can be replaced by a 1988 up transmission for a better feel. The wires
    don't have to be hooked up on a 1985 up transmission. This works well on the
    early S-10 Blazer, because when they get old it will rattle when the torque
    converter locks up. On 1982, 1983 and early 1984 transmissions the
    transmission will burn up if the torque converter doesn't lock-up."

    Doug
     

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