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87 700r4 lock up issues

Discussion in 'Transmission & Transfer Case' started by ClarkUsa1, Jan 20, 2021.

  1. ClarkUsa1

    ClarkUsa1 Junior Member

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    Joined:
    Jan 19, 2021
    Location:
    Ky
    First Name:
    Chris
    Truck Year:
    1987
    Truck Model:
    R10
    Engine Size:
    305
    I’ve never had it to the floor to see if it locks in drive,but I’ve throttled it hard enough that it shouldn’t lock In drive and it does. It locks as soon as it goes to drive every time.id prefer to only have lock up in overdrive
     
  2. 59840Surfer

    59840Surfer Member

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    72
    Joined:
    Oct 8, 2020
    Location:
    Montana
    First Name:
    Joe
    Truck Year:
    1986
    Truck Model:
    K5
    Engine Size:
    350 Stroker to 383 with a 400 crank, Crane Cam, Q-Jet, single 3.5" exhaust..
    Previous dates - up to about '86 1/2 don't use any form of a full duplex ECM - nothing that is actually controlling shift points or TCC, etc.

    ►There was HEI but I believe by 1988 1/2, they started using an infantile version of an ECM with a feedback carb system (TPS, ISC, CTS, 02S, etc) to run things until around early 1990 or so when FI CPFI was running.

    My July 1989 K5 had a feedback carb, a THM700R4 (no real computer functions) a 4-wire distributor, and the first serpentine fanbelt.
    • They used a governor, throttle cable and quadrant position for all automatic up and downshifts.
    • The TCC application is modulated by the throttle cable and governor speed/pressure coupled with the quadrant position with some other considerations.
      • There is also a small vacuum switch on the firewall that senses manifold vacuum to confirm TCC application/disconnect at various vacuum settings.
      • That firewall switch also qualified the TCC disconnect if the vacuum dropped below a set threshold (eg: WOT)
      • There is also a BOO switch to de-couple the TC when you apply the brakes.
      • TCC was also not allowed in LOW, REVERSE, Park, Neutral nor 4WD.
      • TCC is not supposed to apply below a certain road speed and/or when the engine coolant is not warmed up sufficiently - remember these were carbureted engines, not FI.
      • THM700R4s never used that "little module" behind the speedo to regulate anything because that was ONLY a Hall effect signal generator for Cruise Control. I am positive of this because I took it out when I digitized my dash and deleted that sensor.
      • I am not sure if that speedo signal generator was eliminate when an ECM was introduced - at least I think it wasn't in the early versions. If so, it would require a VSS to send a digital signal to the ECM to activate CC.
      • There is a "burp switch" inside the transmission that momentarily released the TCC during an upshift to keep your teeth in your mouth.
      • There was (probably still is) a thermo-switch inside the transmission that reads the ATF temp and forces TCC/LU in lower gears (except 1st/LOW) to drop operating temperatures inside the transmission, because gears don't generate much heat and clutches don't slip - just locking the convertor drops the big heat generator!

    Sometime after 1990, they used a VSS, replacing the old speedo-drive with the cable.

    Up to 1994 1/2, the transm was a Governor-throttle cable-quadrant controlled unit and had no electronics in it except the kick-down and TCC.

    As to it not applying TCC at WOT - that's wrong. Just ask me how many sprags I've blown in a TCC Convertor at WOT!
     
    Ricko1966 likes this.
  3. Ricko1966

    Ricko1966 Full Access Member

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    Location:
    kansas
    First Name:
    Richard
    Truck Year:
    1975
    Truck Model:
    c20
    Engine Size:
    350
    As to it not applying TCC at WOT - that's wrong. Just ask me how many sprags I've blown in a TCC Convertor at WOT!

    Okay. How many sprays have you blown in a TCC converter at WOT?

    Happy now?
     
  4. Itali83

    Itali83 Full Access Member

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    Joined:
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    Location:
    Maine
    First Name:
    Ben
    Truck Year:
    1982, 1987, 1987
    Truck Model:
    K10, 'burban C10, Jimmy
    Engine Size:
    350, 6.2, 350
    not trying to argue but absolutely not. With things working properly. Converter lock under WOT should never happen. On pre tbi motors, there’s a vacuum switch that controls lock up. At wot there’s no vacuum, therefore no lock up. On tbi trucks, the ecm sees wot and won’t lock. I’ve got both generation trucks and have only had 700r’s. Tellin ya man.

    Ben
     
  5. Ricko1966

    Ricko1966 Full Access Member

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    Joined:
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    Location:
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    First Name:
    Richard
    Truck Year:
    1975
    Truck Model:
    c20
    Engine Size:
    350
    Well I guess you can't please everybody.59840surfer requested someone ask him how many sprags he's blown up. So I asked him just trying to be hospitable. But I think Itali83 didn't get it.
     

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