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Lockup Question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Chevit, Nov 26, 2003.

  1. Chevit

    Chevit 1/2 ton status

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    I have an 84 K5 T/700R tranny, can some one explain to me "lockup" and how the vacume switch on the firewall (TCC switch I think)works, and if there is anyway to tell if it is bad... /forums/images/graemlins/confused.gif
     
  2. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Lockup is where you have a clutch in the torque converter that "locks" the converter not allowing it to slip. It is basically like having the clutch pedal out on a manual tranny because if the converter is locked when you try to come to a stop it will kill the motor. The idea is that you have a solid connection through the tranny that doesn't allow any slipage so much less heat will be made and it also effectivly lowers your RPM's by about 100 giving you just a little bit better fuel economy(roughly 1MPG more versus unlocked conv.) I have a toggle switch and relay that I am going to install that way I can manually control the lock up to keep the tranny cool when towing. As far as the vaccuum switch, I think it is all electrical. there is a selanoid inside the tranny that activates the lock up feature.
     
  3. Chevit

    Chevit 1/2 ton status

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    thanks for the info, let me explain why I ask. I had my tranny rebuilt three years ago and it never seamed right. When I first picked up my rig it was really slamming gears hard so I took it back and they adjusted the TV cable and all seamed good when I left the shop but after driving it awhile I noticed that when I really but my foot into it It would slip into gear rather than a solid shift, and it does this through all shifting points. So I went to take it back to the guy who rebuilt it and he had passed away. So I have tried adjusting the TV cable ect but to no avail it still shifts really sloppy so I have learned to control the shifting with the gas pedal. I have changed the tranny fluid several times and all is good with the fluid with some very very minor sludge in the pan. So what am I missing or did the guy who did the rebuild just do a $hitty job? Or could it be somthing with the TCC switch? I'm lost.
     
  4. HarryH3

    HarryH3 1 ton status Author

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    Slipping, or slow shifting between gears doesn't have anything to do with the TCC. /forums/images/graemlins/frown.gif It's quite possible that he had installed some type of shift kit to firm up the shifts. He probably changed a line-pressure spring inside the valve body afterwards, to soften the shifts for you. A good tranny guy could probably swap out the spring for something that would make it shift slighty firmer, without feeling like the shift kit is set on "stun". /forums/images/graemlins/wink.gif
     
  5. Chevit

    Chevit 1/2 ton status

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    I guess you would call it sloooow shifting, he did install a mild shift kit. I will have to check into that and thanks /forums/images/graemlins/thumb.gif
     
  6. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    It could be something else that is more likely which is one or more of the pistons are losing pressure around the rings at higher pressure levels in the transmission(when you floor it) Most of the rings in stock rebuild kits aren't very good and can lose pressure even when newer which is why my local tranny shop used high performance/high pressure rings in my tranny. I have a corvette servo instead of a shift kit with a modified valve body for more flow and my new 700R4 shifts nice, firm, and quick at any power level without that violent slam into gear under light power like I had with my 700 before the upgrades and rebuild. When I would floor it, it would shift VERY soft like you described. What happens is with a shift kit or corvette servo, it applies more pressure to the clutches to get a faster and firmer shift. Obviously if you have a hydralic leak inside the tranny it will not give the pressure to the clutches when it needs it under heavy power input(flooring it) resulting in a lazy soft shift.
    Ok I'm done. /forums/images/graemlins/grin.gif
     
  7. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    What do you plan on doing Chevit? /forums/images/graemlins/ears.gif
     
  8. Chevit

    Chevit 1/2 ton status

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    I can honestly say at this point I really do not know /forums/images/graemlins/confused.gif
     
  9. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    If I'm right on whats wrong with it I would drive it until it blows or until you can afford to have it torn apart again. I drove mine for a long time in the condition that you described but the hard shfting will just get worse as time goes by. /forums/images/graemlins/frown.gif
     
  10. Chevit

    Chevit 1/2 ton status

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    [ QUOTE ]
    If I'm right on whats wrong with it I would drive it until it blows or until you can afford to have it torn apart again. I drove mine for a long time in the condition that you described but the hard shfting will just get worse as time goes by. /forums/images/graemlins/frown.gif

    [/ QUOTE ]

    It is not hard shifting it is soft shifting, proly leave it for now or maybe play with the TV cable some more.
     
  11. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I gathered from your above posts that it only shifts hard under light throttle and shifts soft under heavy throttle.
     
  12. Chevit

    Chevit 1/2 ton status

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    Guess I am not very good at explaining, it shifts fine under normal throttle, it is only when I put my foot into it is when it shifts slow or sloppy... /forums/images/graemlins/blush.gif
     
  13. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    OK, I understand now. I had really hard shifts because my clutches were old and burnt causing them to slam into gear like that. Sounds like you just have some cheap rebuild kit rings that leak when a lot of pressure is put to them. They probably don't leak at normal throttle because there isn't enough pressure applied to them.
     
  14. 84_Chevy_K10

    84_Chevy_K10 Banned

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    From what I hear, it's the 2-4 servo that causes the bad shifts, not clutches. If your clutches were worn out it'd slip like crazy.
     
  15. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    From what I hear, it's the 2-4 servo that causes the bad shifts, not clutches. If your clutches were worn out it'd slip like crazy.

    [/ QUOTE ]
    I didn't say his clutches are worn out, I said pressure is bleeding off around the rings.
     
  16. k5guyva

    k5guyva 1/2 ton status

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    [ QUOTE ]
    As far as the vaccuum switch, I think it is all electrical. there is a selanoid inside the tranny that activates the lock up feature.

    [/ QUOTE ]

    On a 700R4, there is a vacuum switch on the firewall. This is to check the vacuum and disable the lockup if you bury the gas pedal. There is also a switch to the brake system that will unlock the TC if you slam on the brakes.
     
  17. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    [ QUOTE ]
    As far as the vaccuum switch, I think it is all electrical. there is a selanoid inside the tranny that activates the lock up feature.

    [/ QUOTE ]

    On a 700R4, there is a vacuum switch on the firewall. This is to check the vacuum and disable the lockup if you bury the gas pedal. There is also a switch to the brake system that will unlock the TC if you slam on the brakes.


    [/ QUOTE ]
    I don't have a vacuum switch on mine, the TV cable and CCC control it. And you don't have to slam on the brakes, it will unlock by just barely pushing the brake.
     
  18. dyeager535

    dyeager535 1 ton status Premium Member

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    You *sure* your truck doesn't have a vacuum switch? Not doubting you, just trying to figure out which trucks/when went to an ECM controlled lockup.

    CCC systems on cars had lockup managed by the ECM, it only makes sense trucks would have.

    Meaning all CCC and TBI trucks had no standalone lockup system, where the non-CCC/non-injected trucks did, if indeed yours doesn't have a vacuum switch.
     
  19. BlazinRojo

    BlazinRojo 1/2 ton status

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    [ QUOTE ]
    You *sure* your truck doesn't have a vacuum switch? Not doubting you, just trying to figure out which trucks/when went to an ECM controlled lockup.

    CCC systems on cars had lockup managed by the ECM, it only makes sense trucks would have.

    Meaning all CCC and TBI trucks had no standalone lockup system, where the non-CCC/non-injected trucks did, if indeed yours doesn't have a vacuum switch.

    [/ QUOTE ]

    my 83's lockup was under control of the CCC originally. Now, I have a manual switch, since the CCC isn't hooked up to anything anymore.

    [ QUOTE ]
    I don't have a vacuum switch on mine, the TV cable and CCC control it. And you don't have to slam on the brakes, it will unlock by just barely pushing the brake.

    [/ QUOTE ]

    that's correct, the TCC is actually disabled with the same switch that disables cruise control when you lightly press the brakes. A good way to test to see if your lockup is working correctly is in 4th gear to accelerate firmly (but not enough to make your tranny downshift to 3rd), and very lightly press the brake pedal. You should hear your engine revs jump up when the clutch disengages.
     
  20. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    Meaning all CCC and TBI trucks had no standalone lockup system, where the non-CCC/non-injected trucks did, if indeed yours doesn't have a vacuum switch.

    [/ QUOTE ] I would fall into that CCC catagorie so that answers that. I don't need to test my lockup because It isn't hooked up. I disconnected the CCC when I put my 406 in. I plan to just use a 5 way relay and a togal switch to wire the lockup back up. The 5 way relay will be connected to the brake lights and as soon as I step on them the relay will kick the lockup off. Basically just like the aftermarket kits are designed. I haven't thought about what it will do when I put a lot of throttle to it. /forums/images/graemlins/thinking.gif sorry we hijacked your thread Chevit.
     

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