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700r4 slips a bit going into OD

Discussion in '1936-Present Suburban' started by will89, Feb 7, 2003.

  1. will89

    will89 1/2 ton status

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    I can tell that it is slipping a bit when I shift it into od. If my foot is on the pedal light it slips a little longer but if I have a bit of throttle on it it slips less and goes in quicker. Once it engages it is fine. I just wonder what it means.
    Is OD on its last legs? Or does it just need an adjustment and I can squezze a few more miles out of it? Im really easy on it. Never tow with it, always go up hills in D, and Im never in OD til 60mph or so on the flats.

    I know the 700r4 isn't the best endurance tranny ... but I sure love it when its purring in OD.
     
  2. ken

    ken 1/2 ton status

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    It's on its way out!! Believe me, I went through 6 700R4s before finally getting so disgusted with them that I installed a turbo 400.
     
  3. will89

    will89 1/2 ton status

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    How much time do I have? Can I have it adjusted?

    When it does crap out will it just be OD? Will I still have drive?
     
  4. ken

    ken 1/2 ton status

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    I don't believe so...just go easy on it to eek more miles out of it!!
     
  5. heavy4x4

    heavy4x4 1/2 ton status

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    How severe is this "slip?"
    Is it like the tranny completely "disconnects" from the engine letting it rev freely?
    Or, is there still some power being applied to the wheels? If so, don't sweat it...the torque converter just isn't locked yet. Try this....when you're cruising in o.d. and the torque converter is locked - stomp the pedal down to about the 2/3 - 3/4 mark. Your converter will unlock because of the way the tranny is designed (don't ask me why it is set up like this, but it is). Now, if this slight downshift feels just like the "slipping" going into o.d, don't worry about it....like I said, it's just the unlocked converter.
     
  6. HarryH3

    HarryH3 1 ton status Author

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    </font><blockquote><font class="small">In reply to:</font><hr />
    Your converter will unlock because of the way the tranny is designed (don't ask me why it is set up like this, but it is).

    [/ QUOTE ] It's because the lockup clutch on the torque converter can't take much torque. To make it live, GM designed it to unlock when you get on the pedal. On the TBI trucks the throttle position only has to change by 2% for the ECM to tell the torque converter to unlock. On earlier trucks there's a vacuum switch that detects manifold vacuum and decides when to unlock the converter.

    However, there shouldn't be any "slip" going into any gear. On every 700R4 that I've had, the 3-4 shift felt just like any of the other shifts. Then you can feel the revs drop slightly once the converter locks. /forums/images/graemlins/cool.gif
     
  7. heavy4x4

    heavy4x4 1/2 ton status

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    Thanks for the explanation...I knew there had to be some logic behind it.

    </font><blockquote><font class="small">In reply to:</font><hr />
    However, there shouldn't be any "slip" going into any gear. On every 700R4 that I've had, the 3-4 shift felt just like any of the other shifts. Then you can feel the revs drop slightly once the converter locks.

    [/ QUOTE ]
    Right, that's what I was trying to say. From what I understood - he was experiencing this slip when manually shifting from D to OD. So, that's what I was trying to explain....when shifting into OD, the revs will be a bit higher because the torque converter isn't locked, but then the rpms will drop a bit when it locks. Otherwise, yes, there are no "slips"/free reving moments in the 3-4 shift.
     
  8. will89

    will89 1/2 ton status

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    When I put it into OD it just doesn't egage that fast. It doesn't slip in the sense that the rpms go up its just slow to engage- just not a tight shift

    I'll try what you said. But if I stomp on it will downshift. It ususally downshifts somewhere between 2/3 &amp; 3/4 of the pedal. When it does that its a nice tight shift. It jsut going into OD off of the column.. just a bit slow. Maybe its normal.
     
  9. heavy4x4

    heavy4x4 1/2 ton status

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    Well, don't stomp it because like you said, you'll downshift into 3rd. So, I guess I should have stated it differently...depress the accelerator until you feel the t.c. unlock....see if that's what the slipping into od feels like.
    I'd say what you're describing is normal and is nothing to worry about...for now. /forums/images/graemlins/thumb.gif
     
  10. will89

    will89 1/2 ton status

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    What exactly is happening when the tc locks or unlocks?
     
  11. heavy4x4

    heavy4x4 1/2 ton status

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    QUOTE I COPIED FROM www.howstuffworks.com -
    "At higher speeds, the transmission catches up to the engine, eventually moving at almost the same speed. Ideally, though, the transmission would move at exactly the same speed as the engine, because this difference in speed wastes power. This is part of the reason why cars with automatic transmissions get worse gas mileage than cars with manual transmissions.

    To counter this effect, some cars have a torque converter with a lockup clutch. When the two halves of the torque converter get up to speed, this clutch locks them together, eliminating the slippage and improving efficiency."
    READ THE WHOLE T.C. ARTICLE HERE
    I could have explained all that, but this was much easier /forums/images/graemlins/thumb.gif /forums/images/graemlins/grin.gif

    As far as how it locks it in our vehicles: it is electronically controlled via the 4 prong plug mounted above the pan on the driver's side of the tranny.
    Hope that explains it pretty well.
     
  12. will89

    will89 1/2 ton status

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    Thanks heavy, thanks harry. I think you guys are right that its just the tc locking up. It got me a bit worried as Im not yet ready for a major expense.

    Thanks for the article link heavy- good explanation
     
  13. bpiccioni

    bpiccioni 1/2 ton status

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    Steve

    Just when I was afraid that I had been to every good website on the planet, you came through with howstuffworks.com! /forums/images/graemlins/thumb.gif That's a GREAT site - cant believe I never stumbled onto it!

    In return, I recommend www.slickdeals.net (if you know about it, lemme know and I'll give up another /forums/images/graemlins/laugh.gif) - it has 'good deals' posts when they are fresh - I've gotten more than a few items free after rebate as a result of that site.

    Ben
     
  14. heavy4x4

    heavy4x4 1/2 ton status

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    Yeah, I know...howstuffworks is AWESOME...I've spent hours on there before just reading and learning new, cool stuff. /forums/images/graemlins/grin.gif
    Thanks for the link...no I hadn't see that one. /forums/images/graemlins/thumb.gif
     
  15. Okiemuddog

    Okiemuddog 1/2 ton status

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    Hey, I was just scrolling through and thought I would drop another good link for info. 700r4.com It has a lot of explanation of TC lock up and the 700r4 in general. /forums/images/graemlins/thumb.gif /forums/images/graemlins/k5.gif
     
  16. Ddragggon

    Ddragggon 1/2 ton status

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    I am both shocked, and ashamed for not sharing the magic of Howstuffworks.com with everyone. I learned how 2stroke motors work from there, as well as tons of other odd stuff...
     

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