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700 searching in OD

Discussion in 'The Garage' started by 77crewcab, Jan 26, 2007.

  1. 77crewcab

    77crewcab 1/2 ton status

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    Just noticed this today, that when in OD especially with the cruise activated the trans seems to be constantly hunting. Just wondering if someone had an idea what to look for. I have already set the TV cable correctly.
     
  2. 84 K5 4x4

    84 K5 4x4 1/2 ton status

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    I dont know if it helps but i heard the early 700's had a valvebody problem. I had problems with mine for about 5 years. Then 3 rebuilds later i lost it and got a 465/205.
     
  3. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Is the trans actually coming out of O/D, or is it just locking up and unlocking a bunch?

    The vaccum switch might be going bad, and is more sensitive than it is suppost to (assuming a carbed truck)
     
  4. MTChevy

    MTChevy 3/4 ton status Premium Member

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    i have this same problem with my 92 Chevy with the 700R4, actually comes out of OD
     
  5. 77crewcab

    77crewcab 1/2 ton status

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    It is a carbed truck (86 burb) and I am not really sure if it is coming out of OD or not. It will rev and then idle down and then repeat in a quick sequence. I tried just putting it in D and then engine sounds the same as when it is reving in OD so maybe it is kicking out of OD. It is also doing some slight bucking every so often and shifting kinda slow. This trans was rebuilt last spring but set undriven for about 6 months. This is my first 700 and I'm just not sure where to start looking.
     
  6. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Well, first we gotta find out if it is the tranny coming out of lockup, or out of O/D. Next time it does it, put your left foot on the brake just enough to turn the brake lights on, and also therefor kill the power to the lockup solenoid, and see if it stops hunting between. If it does, then I'd be looking at getting a vaccum switch that needs a lower vaccum rating to be unlocking the converter, if it still does it, I'd tend to say it is probally a TV cable issue.

    By shifting slow, do you mean it is holding gears longer than you'd expect it to, or is it shifting in a short, stacked sort of a manner? If its short and stacked, do NOT drive another minute with it, cause you'll kill your tranny in no time at all, you need to turn your TV cable pressure up until it shifts properly. Turning it up involves sliding it towards the firewall, turning it down involves sliding it towards the throttle linkage.

    MT, does your tranny shift normally otherwise? 305 or 350? Do you put the skinny pedal down further to keep your speed, which makes it come in and out?
     
  7. BoondocK5

    BoondocK5 1 ton status Author

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    Are you sure it's not the lock up converter, locking and unlocking?
     
  8. 77crewcab

    77crewcab 1/2 ton status

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    Looks like a poor vacuum signal is probably the culprit. I started looking at all the vacuum lines under the hood and it is FUBAR. Since I don't have to deal with smog and the smog pump is already seized up I am going to look at just pulling all that crap off and run only the essentials like on my old truck. What will I have to keep that is related to an 86 with 700 specifically?
     
  9. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Just the vaccum line, and inline delay canister that goes to the vaccum switch, your thermac valve stuff, and your vac advance.
     
  10. 77crewcab

    77crewcab 1/2 ton status

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    Well today either the tranny or the TC went out completely. Found out that the TV cable sheath was broken about midway down and so the adjustment didn't do much good. I will be replacing it this weekend with one from a 90. Anything I should be aware of on the swap? I will most likely be rebuilding the 86 one and put it back in in a month or so, so this one from the 90 will only be temporary most likely.

    On the smog stuff I guess I am a little confused. I know I can plug the dist advance strait to the carb, can I not plug the vacuum/electric switch for the trans strait to the carb as well? What is the delay canister for? And what is the thermac stuff. Is that the valve on the intake hose to the air cleaner. If so that is not hooked up at all as of now, so should I hook it up? What about the fuel vapor canister? I don't mind keeping it but just want to cut down on all the extra spaghetti lines. Can I hook it strait to the carb as well? Thanks for all the help.
     
  11. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    yeah, your bands will be roasted in that tranny if it had next to no pressure due to the broken TV cable.

    The 86 and 90 tranny are basically the same on the outside, and the lockup stuff should be pretty similar as well. The 90's tranny has better components inside though, and is tougher than the 86 version.

    You want the vaccum switch for the transmission plugged straight into an intake manifold vaccum source, you don't want it hooked up to ported vaccum. The delay valve is in there to keep the lockup from being very sensitive, and delays unlocking the converter for a few seconds by only allowing so much air to re-enter the vaccum switch.

    The Thermac stuff is indeed the heat riser valve on the air cleaner, If you don't have the heat riser hooked up, then you can just block those lines off.

    You can do without the charcoal canister on a carbed rig, it just sucks the fumes off the top of the tank, and "enrichens" the mixture with it. On a EFI setup, its far more important as it serves as a way for excess vapour pressure to be vented straight into the engine instead of into the atmosphere. My 77 is TBI, and doesn't have a canister, and the gas smell coming off the fuel tank vent up front is pretty powerful at times...
     
  12. 77crewcab

    77crewcab 1/2 ton status

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    Okay on the vacuum switch, I have 4 ports 2 on top and 2 on the bottom like the 4 on a dice which port is which. I mean which port goes to the carb and which to an accessory?
     
  13. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    That sounds like a temperature actuated vaccum switch... The vaccum switch for the transmission is a round canister with a single hose going in one side, and two wires going in the other.

    That temp switch would be used to control other emissions systems on the truck, and really isn't nessessary in a bare bones application.
     
  14. 77crewcab

    77crewcab 1/2 ton status

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    Thats the one by the wiper motor right? So the hose should go from there to the little delay canister thing and then strait to a manifold vacuum source correct?
     
  15. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Yep! If you need / want a pic of it, lemme know, and I'll snag a pic off my 77 before it sells...
     
  16. 77crewcab

    77crewcab 1/2 ton status

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    I know which one you are talking about just had something else in mind at first.
     

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