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700R4 Lockup

Discussion in 'The Garage' started by Hossbaby50, Feb 17, 2004.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

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    Location:
    Peoria, AZ
    How exactly do I make sure my 700R4 is locking up?

    Until today I could see the RPMs when shifting drop. It would shift 3-4 and the RPMs would drop initially to say 2100 then down again to 1900. I am assuming that the second drop is the lockup. Is that right?

    Today though I was monkeying with the TV cable and now I am not getting the second drop at all in ANY position of the cable. How do I check the lockup circuit and I have heard there is a lockup fuse. Where?

    The reason I am monkeying with the cable is I am getting jumps in my RPM in OD at cruise. Jumps back and forth when I am around 2000 RPM. I am pretty sure it is the TC locking and unlocking. So I was adjusting the cable to try and get rid of that. Now no lockup at all.

    What wiring in the 4 pin connector on the trans is involved in the lockup process if any? Where does it go? Thanks

    Harley

    p.s. my torque converter is supposed to be a low stall. 1400-1600 rpm or there abouts.
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Harley on mine the little solenoid with vacuum hose on firewall near the brake booster went bad and mine did same thing. I got it at brown and brown for 40 bucks. It basically uses engine vacuum to know when your cruising or idling. yours being 2 years newer just not sure if you have it or not.
    Paul
     
  3. AZ_Overdrive

    AZ_Overdrive 1/2 ton status

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    My 89' Burb has the EXACT same problem. I have been fighting with it for the past year! I posted about the issue and received a few tips but none of them worked.
    1. Replace/adjust TPS
    2. Replace MAP
    3. Checked distributor shaft for excessive play.

    Nothing worked. pauly383k10, I am not sure I have that little vacume solonoid. I will check latter today.

    I did however purchase an AutoXray scanner and noticed that the computer is showing 4th gear in/out at the same time the TCC is locking and unlocking. So, I am assuming that something is telling the computer that the trans is going in and out of OD when it is not. Hence the TCC locking and unlocking. I talked to a few tranny shops and they all reported that the 4th gear switch inside the trans either works or it doesn't, not intermintently. So, there must be a short or something along the wiring path from the trany to the computer. I am out of ideas!

    It seems like it has to be a simple problem since there are so many people with Blazers and Burbs that have the SAME problem....
    /forums/images/graemlins/burb.gif

    P.S. I live in Chandler so if you want, we could meet up and hookup my scanner to your truck to see if your problem is the EXACT same as mine.
     
  4. Hossbaby50

    Hossbaby50 3/4 ton status

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    When I did my TPI swap I didn't install a VSS (yet) so my computer thinks its in park all the time. So I know the computer is not the problem and I wouldn't be able to read it with a scanner.

    I am going to look for that little solinoid and see what I can see. I might just need to switch to the VSS and let my computer lock and unlock the converter instead of the manual system that came with my truck. I know the guys at the trans shop when I had my 700R4 rebuilt about 6 months ago were having problems with the lockup too and they thought they had it fixed. Apparently not. I will have to take it back since it is under warranty.

    Harley
     
  5. az-k5

    az-k5 1/2 ton status

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    You can also bypass the automatic lock up and use a switch to control it. Or get a manual & 205 then sell me you combo /forums/images/graemlins/grin.gif
     

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