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TH400 kickdown / detent cable

Discussion in 'The Garage' started by dremu, Feb 10, 2006.

  1. dremu

    dremu Officious Thread Derailer Premium Member

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    For those following my crewcab saga, I've been trying to tune the bigblock in my sixpack to actually pull, as she was bloody anemic, even for a sixpack which I recognize is kinda portly :D

    One thing I noticed is that she doesn't want to downshift, say, onto a highway onramp, when I whomp on the pedal.

    Now that I have the timing dialled in and the plugs and wires set up, I figured I'd adjust the kickdown cable.

    There isn't one. :doah: :eek1:

    Now, not having any other big blocks nor gas TH400's to compare to (my only other TH400 is behind a diesel), I donno if this is supposed to be that way ... but somehow, I think the PO got bored one day and did something stupid. (That or BADLY transplanted the tranny from some other truck, so this confirms my suspicion that the engine/tranny may not be original.)

    So, three questions 'fore I toodle off to the boneyard tomorrow.

    1. I assume it's supposed to have the kickdown cable, or whatever you wanna call it. Are there any 454's that didn't?

    2. Where does the cable go on a TH400? It's a major PITA to get under the truck (short dually tires, 2WD) so any guidance would be appreciated!

    I've done the cable on my TH350 when I swapped it, so I know (I think!) how to unhook it on both ends and so forth, once I know where it's supposed to go...

    3. When does the kickdown cable do its thing, as opposed to the vacuum modulator? (Explosive X-21 Space Modulator!) I felt her downshift once or twice on a test drive, presumably based on the vacuum, but even that may need a bit of adjustment.

    -- A
     
  2. Russ

    Russ 1/2 ton status

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    I don't know what year they started using them, but my 88 crewcab has a downshift relay on the firewall. It will shift normally, but definitely will not downshift when you accelerate if that relay goes out.

    Russ
     
  3. divorced

    divorced 3/4 ton status

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    400's don't have a cable. Here is a pic of the gas pedal bracket from an '86. You can see the switch that kicks down the transmission.

    [​IMG]
     
  4. goldwing2000

    goldwing2000 Guest

    Yup. TH400 uses a kickdown switch. Some vehicles have it mounted next to the carb. Apparently trucks have it on the pedal bracket (thanks, divorced).
     
  5. supersize75k5

    supersize75k5 OrganDonorRacing.com

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    huh,


    ive never used a kick down switch with any of my t-400's.

    but I also run a rachet shifter and just pretty much shift as I drive, same with my t-350 I dont use the cable on them, just shift with the rachet shifter,

    anybody else do it this way?
     
  6. K5er4Life

    K5er4Life 1/2 ton status

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    The th400 will kick down when the switch is depressed under the pedal, my 86 crew cab does this and every factory setup th400 I have seen has had this. Though that is not to say that all of them was setup like this but all the the ones I have seen do. There are two inputs for the trans for it to understand what the truck is doing. One is being that switch and the second is a vaccum line that goes to the modulator. They wont kick down very easily, usually you know when you are going to do it because the pedal is pressed damn near close to the floor. I have heard someone say though that 2nd to first 1st diwnshift is based on vaccum drop, but I dont know the truth to this. My crew cab is all stock and I have gotten used to the way the big block and 400 act together. Its kind of cool though because the thing has enough power to just push through the gears without really needing a downshift. Sooner or later its coming out though and getting a "freshen up" rebuild to allow for some desired power. Or you can just drop in a full manual valve body like I did in my blazer and then you will KNOW when you downshift, your face is on the windshield then.
     
  7. dremu

    dremu Officious Thread Derailer Premium Member

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    Okay, thanks all ... saves me a trip to the Pick-my-nose. Now to see if that switch is there (any bets? I found bailing wire, honest to god, holding the parking brake cable in!) ... and maybe tweak the modulator a hair.

    -- A
     
  8. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    go full manual... then you can have any gear you want at any speed and you don't have to worry about kickdown cables etc. :thumb:

    j
     
  9. josh86k10

    josh86k10 1/2 ton status

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    BMM-20297

    $43.95 at Summit Racing

    (Just in case you can't find one at the junk yard)
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    yup..no cables..its WIRED!

    That switch activates a solenoid in the valve body to downshift the tranny..if the vacuum modulator is hooked up correctly,it will make it downshift into first gear when your in second, when you goose it too,even if the detent switch is disconnected..but it wont force a third to second gear downshift..you either need the detent switch hooked up to do that, or you can yank the shifter into second manually to get "passing gear"..:laugh:

    When I first got my 69 GTO,its TH400's detent switch must have broken..someone put a horn button on the dash,and wrote "PASS" on the button!..:haha: :bow: ...first time I pushed it I almost rear ended the car in front of me!..:eek1: ..mmm OK..now I know what THAT switch does!..:rolleyes:

    I found the correct switch on an olds cutlass of the same vintage,and retired the "PASS" button!..I've seen push button starter switches cobbed onto a carb for a detent switch on a few junkers at the boneyards!.:crazy: ...
     
  11. dremu

    dremu Officious Thread Derailer Premium Member

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    D4Me, your posts are always entertaining :D

    Anyway, I'll go look under the dash, see if there's a switch there ... where on the tranny would I look to find the solenoid or its wiring, i.e. where's the valve body? (I know, total noob question, but I've only swapped, i.e. looked closely at a TH350 'fore :) )

    -- A
     
  12. divorced

    divorced 3/4 ton status

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    The valve body is the big thing you see when you take the pan off the bottom. There should be a wire (orange or orange/white IIRC) that runs from the switch on the pedal to a connector on the transmission.

    Here is a pic of where I *think* the wire goes.



    [​IMG]
     
  13. roadnotca

    roadnotca 3/4 ton status

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    Yea, a Hurst and TransScat kit, bang shifts up and down. For trails, manual shift and lockers can get you anywhere; thats with a Big Bootie Burb. For DD though, I just let Otto do the work. TH350.:D
     
  14. dremu

    dremu Officious Thread Derailer Premium Member

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    The gutless wonder awakes!

    Well, there's a switch there alright, but it never ever actually closed, even when I whang the gas pedal down all the way. Checked a coupla others, all the same, so the switch wasn't defective. I veeeeeery carefully bent the pedal rod veeeeeeery slightly in (less than 1/4" along the outer arc) so that it DOES close the switch when mashed ... and adjusted the bracket on the carb the same way, so as not to idle at 2000 RPM :haha:

    Between the kickdown switch actually working and a little massaging to the vacuum modulator ... wow, it's like a new truck. (Well that and having the timign dialled in is good too :D )

    Once again, thanks to all out there in CK5 land ... my sixpack, while still a pig, at least can get out of its own way!

    -- A
     
  15. 79k20350

    79k20350 3/4 ton status

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    i added a piece of rubber hose around my pedal rod, that made all the differance!it made the switch fully open and the truck started to take off.
     
  16. dremu

    dremu Officious Thread Derailer Premium Member

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    I was tempted to do something like that, but it seems so ... I donno, temporary :) My next step was gonna be to weld a new edge onto the pedal rod, but this seems to have done the trick.

    -- A
     
  17. 79k20350

    79k20350 3/4 ton status

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    originally it was just temporary, but it worked so well i just kept it. if it aint broke dont fix it, right?
     
  18. goldwing2000

    goldwing2000 Guest

    If it ain't broke, you ain't wheelin' hard enough. :D
     
  19. dremu

    dremu Officious Thread Derailer Premium Member

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    Wheeling? In a 2WD sixpack? :haha:

    backup-lights-redux-5.JPG
     
  20. goldwing2000

    goldwing2000 Guest

    Well, not you! 79k20350 is the one who the reply was aimed at.

    I have been wheeling in a 2WD before, though. I got stuck, but at least I was out there. :D
     

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