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one more lockup question...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by MNorby, May 3, 2002.

  1. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    Hey there. Eveyone has been a big help on my tranny issues. I got it going again after blowing up the torque converter and pump. I got hte TV set properly again but still not locking up. My questions is that vacuum line that goes to the wires to the tranny, does that vacuum go to the carb at the same port teh vacuum advance hooks in? Also, that swtich the vacuum hits, does that go out very often? It is hooked up but still not locking up in 3 and 4. Thanks for the help all!
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    I have no clue about longevity of that switch..I'd say its unlikely to fail...but you should be able to apply vacuum (suck on it) and it should hold...could probably test that with a multimeter, since you can't see the plunger/diaphram.

    That switch should be fine with straight manifold vacuum (unlike advance if its hooked to the carb) as the converter needs to unlock when the throttle is opened quickly, when manifold vacuum will drop.
     
  3. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    maybe that is why she isn't locking then, It is off a T off the carb going to the vacuum advance. I'll see about that port between the carb and distributor
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Yep. Lockup at cruise, but not WOT is the goal.
     
  5. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    well now I feel stupid. It's been hooked up to vacuum advance since I put the new motor in. DOH!
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Well vac advance is similar, except that the carb port is supposed to be ported. Vac advance drops off as vacuum decreases, but I'd still hook the switch up to manifold vac to test.
     
  7. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    I'll try after work. What do you mean by carb vacuum port is supposed to be "ported". I guess I don't understand
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    The carb port for vac advance ONLY sees vacuum under certain throttle openings. EGR is the same way. There are slots/holes cut or drilled into the primary venturi wall, when the throttle opens far enough, (like above idle just as an example) the "port" in the wall is uncovered, and "sees" vacuum, thus, whatever is hooked to that port does also. If you pull the vac advance line off your carb at idle, it should not affect idle hardly at all, if any, as there is no vacuum "seen" by that port.
     
  9. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Since when does a 700R4 have a vacuum line going to it? 700's don't use modulator valves like TH350's and TH400's.
     
  10. I am a little lost bafter reading your posts but I have a TH400 with lockout and as far as I know, it's not locking out. How do I go about checking this and fixing it? Thanks 80K20
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Since always? It's not actually going TO the tranny, it's a vacuum switch bolted to the firewall, with the input from that switch helping govern lock/unlock.
     
  12. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I talked with several tranny shops today and they all said there is no vacuum switch on a 700, unless someone installed a 700 in a car/truck that doesn't have a computer and then there is a switch that does use vacumm to disengage the lock-up converter. I have an 89 blazer and there is no vacuum switch anywhere.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Well, as is to be expected anymore, they are all idiots. I was a bit hasty in my reply, I would not be surprised if '87 and later 700's don't use a firewall vacuum switch, I believe they had input from somewhere else.

    However, if the truck has VSS ('82-up) and was not injected or CCC (Electric carbed) it's gonna have a vacuum switch. I've owned an '83 w/700, and I've got a few of the systems in my garage, so I can run "factory" lockup without the computer if I wish....but the fact is, all require VSS, and all require the vacuum switch, and all feed into the "box" under the dash on the drivers side. Again, I'll clarify, up to '86 at least.
     
  14. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    Yes, mine has a vacuum actuated switch on teh firewall that then tells the wires to the tranny what to do....
    Here are a few links to my drawings of the wiring diagram I made and the pic of the harnes:
    http://tellico.off-road.com/wwwthreads_uploads/765925-trannywire.jpg
    http://tellico.off-road.com/wwwthreads_uploads/765927-tranywire2.jpg
    Which plugs on the tranny connection should be hot for lockup to occur? I checked the vacuum switch and if I suck hard enough it opens so that is good. I found a bad connection on the wire plug from the braks so I will make a jumper connection to fix that but for now I made it hold so it connects. The one plug is always on if brakes= off and the other 2 can be on if vacuum is on and/or that myster wire is jumpered together. Any ideas? Thanks so much
     
  15. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    Is one of those wires supposed to be a ground possibly????
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    I *think* perhaps that mystery wire is supposed to be going to the ALDL connector in the cab...if you ground one wire in the aldl connector (jumper pins a and f IIRC) you can force lockup.

    Take a look at figure 2 in the '85 diagrams. http://community.webshots.com/user/ausername11/2

    Does that clear anything up? I'd browse around through those pages though and see what you can come up with. GM didn't change wire colors or routing unless they *had* too, but the TCC/tranny setup changed enough that I think probably every year something was slightly different...but that manual is only one year different than your truck, so it should be real close....

    Hell, theres the low vac solenoid I couldn't find for the other post either lol. Looks like those perhaps are not ALDL wires, but for another sensor. (upper left corner of fig 2)
     
  17. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    cool site. I'll do some checking. Do you know if one of those wires is a ground by chance though? Thank again so much!
     
  18. dyeager535

    dyeager535 1 ton status Premium Member

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    Again, no electrical expert, but I believe the switches and etc all wired into that circuit actually complete ground...two wires to the TCC solenoid, and the circuit is grounded only after meeting the criteria for all sensors. So basically imagine the current is allowed to flow through the solenoid "in" one wire and "out" the other, when the sensors allow it. If thats wrong, someone feel free to correct me.

    That kinda funky looking lined down arrow thing right next to the words "4wd trans unit" is the symbol for ground though, and since there is no wire mentioned, that probably means the entire transmission is "ground".

    Dorian
     
  19. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    Well, I finally come to the conclusion it is int the tranny. I hooked up a light in the cab to tell when the wire is hot for lockup and it is hot while driving down the road. If I touch the brakes it turnes off. While in OD the tranny acts the same way with the brakes (lights) on or off. I'm gonna take it to the guy that put the tranny together and have him look at it.
     
  20. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    thank you so much for all the help. I think I know tons more about TCC and TV cables than ever before
     

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