Converting an automatic 74 Swinger to a 4 speed

Manual Transmission & Clutch Discussions

  1. yellow rose

    yellow rose Overnight Sensation

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    Very cool.
     
  2. Norm.P

    Norm.P Active Member

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    AJ, I have a quick question. With the TKX transmission, you have that to cut the upper structure of the torsion bar cross member. I have seen and spoken to people who haven't welded in a new upper structure. They just use and rely on the supplied lower bolt-in cross member. Would this be a problem? I too am looking to convert from auto to manual. Thanks in advance.
     
  3. AJ/FormS

    AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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    IMO
    NOT rebuilding the upper hoop is a mistake.
    Sure, you can do it. and Sure the car will be fine sitting in your driveway.
    But what happens when you swap out the slanty T-bars, for 340 bars or 1.03s? and you drive it? Most of the forces that cause the wheel to go up and down, are transferred into the T-bars and from there into the X-memberS. What happens when the bolts holding the X-member slip? and they will.
    The factory X-member is a tie-bar to the hoop; together they transfer the T-Bar forces into the Unibody. Neither of them alone is sufficient. If/when your X-member clamping bolts slip, the whole thing will work itself loose, Be flopped around by the T-bars which will tear out the floor, and then bang out the holes. While that is going on, the Z-bar is drooping, and causing departure woes. In what order this will happen, or how long it will take, I cannot say.

    As for the supplied X-member, I cannot say either, I haven't seen it.

    As for me. I want a hoop there. And I want to raise the tail to factory height to maintain the factory driveshaft angles, for the factory ride height.
    If you change the ride-height or change the power input, you have to rework the rear pinion angle. The 6-cylinder rear springs will have to be replaced if you keep the factory-type suspension.
    You can ignore this and endure the consequences which are.
    Noise, Vibration, Harshness, and broken parts. Not to mention lousy handling.
     
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    • Norm.P

      Norm.P Active Member

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      I was thinking the same thing. I'll just fabricate an upper support (fingers crossed) lol. I have another question. If I have a warmed over 340 that pushes out about 375HP, when selecting a tranny with close or wide ratios, which one would be best suited for my application? I've been told to go with the wide ratio. What do you think? Thanks in advance.
       
    • AJ/FormS

      AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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      For street duty;If you already have a 4-speed, I would try whatever you got.
      Otherwise;
      The big cam required to make that power, with iron open-chamber heads, will rob the low rpm of torque. To get off the line without drama, you will need a starter gear of about 11/1.
      The available A833 ratios are;
      >2.47-1.77-1.34-1.00, the starter is 11/2.47=~4.56s
      >2.66-1.92-1.40-1.00, the starter is 11/2.66=~4.10s
      >3.09-1.92-1.40-1.00, the starter is 11/3.09=~3.55s
      >3.09-1.67-1.00-.73od
      I vote for the Commando 3.09
      I highly recommend NOT to try the 3.09od box with a factory-headed 340 and a 375hp cam. The ratios are just too far apart, and the rpm drops will put your 375hp/340 way off the cam.
      If you go with alloy heads, and bump the cylinder pressure to ~185psi, you will get some bottom-end back, allowing a lower starter gear ; perhaps as low as 9 or 10 to one.
      At 9.0, you can get away with 9/2.66=~3.38s rounds to 3.55s...... maybe 3.23s. Play it safe, and use the 3.55s.

      I like to top out Second gear at about 60 mph, at about 400rpm over the power peak. This will get me to 60 about as quick as possible. To do this with 375hp with a cam that power peaks at about 5200, and 60=5600, this requires a Roadgear of ~7.49.
      In Second this is 7.49/1.92=3.91s with the wide ratios; or
      7.49/1.77=4.23s with the close-ratio.
      I vote the Wide-ratio.
      So in conclusion, the Commando is the way to go, with a rear gear between 3.55 and 3.91.

      IMO;
      >for a streeter that sees more than occasional hiway duty, the 3.55s are already on the high side of comfortable. This makes the Commando the natural choice.
      >At the rising cost of gasoline, 87 octane is looking pretty attractive. To run this with iron open chamber heads, will require a drastic reduction in cylinder pressure, which will just about kill the bottom end at 375 hp absolute. So again requiring more starter gear. This makes abandoning factory heads a natural choice.
      >As a streeter, you are sorta limited to 75/80 mph. With 3.55s and in Third gear(1.40ratio), this comes to about 5000rpm, so your cam COULD peak as low as 4700 rpm and be every bit as much fun as the cam required to make 375 hp. That is about 2 or 3 sizes smaller. Throw in some hi-flowing alloy heads at 185psi and you can drop another cam size. Now you are fully streetable and can run 3.23s, with that Commando.
      In fact, with a cam this small, you might think that the 3.09od might become attractive because your powerband has increased quite a bit. And with the overdrive, you can run almost any rear gear that you might like.
      However the lowest street-starter gear that I would recommend is ~12/1. Therefore the rear gear becomes 12/3.09=3.91s; and overdrive becomes
      3.91 x .73=2.85. And 75mph becomes 2660rpm. However top of Second gear with 3.91s becomes 60=4880
      With 3.91s, 80mph=6500 in Second and just 3900 in Direct, so the big cam will only hurt you in Third gear, and 6500 in Second is way too high for most street cams. Can you go there? Sure . But factory heads will have choked a long time ago. I highly recommend NOT to use this transmission with a factory-headed 375hp 340.
      However,
      with 300/330hp, this is a pretty good combo. The starter with 3.91s is a tire-fryer. And Second is pretty good too. The cruise gear is excellent. Only third gear is a lil lacking; but you almost never use it at WOT, so no big thing.
      But around town, you really need some cylinder pressure to pull it off, because most of the time, you will be in Second gear. This is a Roadgear of 1.67 x 3.91=6.53 Which, IMO, is a lil lacking in Torque Multiplication at low rpm especially for a 340. 30mph will be just 2440 rpm in Second, so your 340 is gonna need some balls down there and a 292/.509 cam is not gonna get you any fun there with factory heads. 40 mph gets you 3250 in Second and still lacking, but at 40 in First, you are already at 6020.
      So; IMO, forget the 3.09od trans for any factory-headed 340.
      I ran this od-trans in a Street-360 with a 223*/110 cam, Alloy heads, and 185psi. I ran that combo with every rear gear from 3.23s to 4.30s, and found no satisfaction in it.
      >The Commando with 3.55s solved most of my problems. The GVod solved the last one.

      I can almost guarantee you that you will hate the starter gear of the 2.47 Close ratio on the street, with anything less than 4.10s.
      The Wide-ratio 2.66, is really not a wide ratio at all, but it still lacks a decent First gear for the street. When you work it out, the splits are very similar between these two.
      I can almost guarantee you that you will like the Commando with 3.55s or better.

      The Swinger is seriously challenged for tire space in the back. This makes running big horsepower on the street with minimum tirespin, impossible; except by restraining your right foot. Which totally negates the purpose of having the power in the first place.
      The most-fun street-combo I have yet built was a 330hp 360 in a 68 Barracuda that accepted 325/50-15s on a narrowed rear end. I finally ran the Commando and 3.55s.
      Happy HotRodding.

      If you already have a 4-speed, I would try whatever you got.
       
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      • jcolman

        jcolman Well-Known Member

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        I've got about 200 miles on my TKX swap. The upper torsion bar cross member was cut without any additional bracing except for the bolt in cross member. So far so good. I do have subframe connectors to help stiffen the whole car. My Torsion bars are stock 318 bars and I'm running a 340 with aluminum heads, fiberglass fenders and hood. 18" wheels. 3:23 gears. I was running down the interstate today at 80mph, turning about 2000 rpms.
         
        Last edited: Jun 26, 2022
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