Kickdowns and Q-jets

Discussion in 'Transmission & Driveline Topics' started by black_aerocoupe, Apr 5, 2016.

  1. black_aerocoupe

    black_aerocoupe Veteran Member

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    I was reading Twisted_Metal's old thread that got bumped today on TH350 to 200-4R conversion.

    One thing I want to know is this: When the Q-jet bellcrank or bracket changed so that a TV cable couldn't just swap right into a Q-jet car?

    I know the '80s TH350-C, 200-4R, 200-C, and 700-R4 cars used the exact same bracket and bellcrank attachment point at least as far back as '83. I've owned a few. And I've converted a few. Remove TH350 kickdown cable, install 200-4R/700-R4/TH200 TV cable, done.

    What changed, and when did it change, such that the aftermarket bracket and possibly bellcrank mods are needed?

    This (supposed) '81 Vette Q-jet from the `bay looks like, it too, would take a TV cable attachment point.

    This (supposed) '69 Chevy Q-jet from the `bay looks like it has a different bellcrank, but I have no way of knowing the hole there is correct or incorrect for a TV cable.

    Who can provide a history lesson?
     

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  2. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Q-Jets have been around a lot longer than TV cables.
    So... They weren't designed with TV cables in mind during the early years.

    If the carb came from a vehicle which originally had an OD transmission, you should be able to use a factory cable with the OD trans and get it to work just fine by setting the WOT throttle position and letting the idle position fall where it may. That's how the factory TV cable was "set".
    (A carb for an 85 Chev pickup with a 700r4 shouldn't require an adapter kit.)

    "Kickdown" (Detent) cables are just a mechanical On/Off valve.
    Adjustment is simple in that it only needs to be pulled full out at WOT.

    A TV cable has more valve functions through its range of motion so the beginning AND end of the pull is critical in regards to the throttle position.

    The TV Made EZ kit is designed for adapting many different carb models (with different kits) and providing the optimal geometry throughout the range of the throttle. (Not just at the ends)

    Very good write-up on the system here--> http://www.tvmadeez.com/article/index.php

    The carb in your first pic is equipped for a car with an automatic trans, cruise control and A/C.
    (Looks just like the 80 carb I've used for the past decade, except for the computer plug.)

    The one in the second pic... I don't know.
    They might make a kit for it if you look at the numbers.

    By researching their site, you may be able to tell when it changed by the kit numbers for conversion.
     
    Last edited: Apr 6, 2016
  3. 77 cruiser

    77 cruiser Veteran Member

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  4. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Great info!

    I have some VERY recent experience in this.
    But I don't know quite what I've learned from it yet.

    I thought the Detent cable and TV cable carb brackets were exactly the same myself.

    I swapped out the 80 carb for one for an 85 Chevy pickup. (Last weekend. Got a deal on a carb.)
    The TV adapter is the same as the one for my 80 carb and it has been working perfectly for years as far as the TV cable function goes.
    I figured I could swap the TV stuff and leave it in exactly the same position. What I didn't think about was the potential difference in automatic transmissions on this carb. (TH350 vs 700R4)

    I cut off the pin for the detent/TV cable (85 carb) and installed the adapter.
    I took a pic to be sure I got it back in the same position and I marked the cable setting with a piece of tape wrapped around it.
    Everything else is aligned with the plate under the carb with no chance of misalignment through four mounting holes.

    I installed the carb and connected the TV cable before I bolted it down to be sure I didn't mess up the adjustment.
    Tape was still in the same position.

    Everything looked good so I took it out for a drive around the block.

    Damn.... Way too tight. :(

    I brought it home and set the WOT position on the TV cable and found it pulled out 3/16" more with this carb!
    (Same measurement mentioned in the link above.... Hmmm.)

    I should have set the WOT position BEFORE I took it out. Potentially dumb move there.
    Thankfully, it was too tight instead of too loose. (Too loose will destroy a transmission in short order.)

    Now I have to break out the transmission pressure gauge and review the setup instructions before I move it again.

    The bracket may look the same and it uses the same TV MadeEZ adapter but there is apparently some slight difference with the ones designed to use a TV cable.

    This really shouldn't surprise me (had I thought of it) as it would be much easier for GM to slightly redesign a bracket on the carb than it would be to design a transmission around an old carburetor bracket.

    Honestly... I can't see the difference with my eye but there has to be something in the design of the bell crank of the 85 carb to make the throttle travel pull the TV cable 3/16" past the WOT position of the 80 carb with all of the other pieces in exactly the same position.

    I almost wish I had swapped to a factory cable to see how that worked but I didn't want to crawl under the car and deal with the transmission end of the TV cable just for a carb swap if I didn't have to.

    Gotta jack it up now and hook up a pressure gauge.

    I'll let you know what I find if I ever figure it out.
     
    Last edited: Apr 6, 2016

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