Which K frame would you use, given the choice?

Suspension, Steering and Chassis

  1. brian6pac

    brian6pac Well-Known Member

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    I never ran one, are they thicker metal ? more header clearance ?
    I know they had better disc brakes, upper control arms were different with bigger ball joints, lower ball joints were bigger for the bigger tie rods and had different center link and spindles. I have swapped out all that on a 70 K-member, but what is better about the k-member.
     
  2. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    Already covered. The 73+ K member allows the sway bar to pass through it, which improves ground clearance and keeps you from using your sway bar as a parking block finder like the earlier style. The way that the bottom plate is changed to allow this makes it more dimensional, with a stamped edge. Of course it also adds holes, so, you can argue about whether that makes it stiffer or not. I would say it’s about the same. The engine mounts are better, the header clearance is pretty much the same because the engine location is the same, although you won’t get changes like with worn out or damaged biscuit mounts. The engine height in the bay doesn’t depend on the condition or thickness of the rubber mount, but instead by the mount on the K frame which is fixed.

    If you’re running BBP brakes and calipers, the 73+ sway bar changes allow for the factory caliper location, so, no need to flip sides to clear the calipers from the sway bar and run longer hoses like with the 67-72 sway bar and BBP brakes.

    Oh, and the 73+ sway bar doesn’t limit front tire width like the 67-72 factory sway bar.

    If you’re planning on running BBP brakes and a sway bar the 73+ K is a no brainer. Even more so if you want wider front tires. You can get it done with the 67-72 K’s with the right aftermarket parts, but it’s easier with the 73+ k and sway bar design.
     
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    • 66fs

      66fs FABO Gold Member FABO Gold Member

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      No, you are wrong. Never would I change a K frame for no reason. I have run them all for decades. The only K frame I changed was a 75 or 76 for a 67 K frame. The 75-76 was falling apart. Geometry is all the same except for the sway bar tabs. In use I cannot tell any difference and I have driven them on the street for hundreds of thousands of miles. If you have a Formula S or a 340 car you have all the good stuff in the front end. As far as the fail safe motor mounts, I prefer the biscuits anyway, a simple drill and tap will do it, plus I tie the drivers side head boss to the frame rail.
       
      Last edited: Jul 17, 2021
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      • Dartnut

        Dartnut Don't hate me because i'm beautiful

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        Unless it's a true ''resto'', and given the choice, I would use the '73 and up spool mount K member every time.
        The same goes for the front suspension and BBP brakes.
        They are better, stronger, and parts are cheaper and more available than the crummy SBP stuff.

        That being said, a lot of people don't know that the real reason Chrysler went to the spool mount K frame and trans mount was for collision purposes.
        Primarily, In a front end collision, the engine would stay in place instead of shearing the mounts and shifting forward.
        The other benefits were with roll overs and side or rear impacts.
        The engine and trans would stay in or close to their original positions.
         
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        • 66fs

          66fs FABO Gold Member FABO Gold Member

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          So if you had an original 1970 340, 4 speed Duster you would change out the HD 340 K frame, front sway bar, and Kelsey Hayes disc brakes to the cheap 73+ K frame and slider single piston calipers? Then change out the 8 3/4 rear to an 8 1/4 rear or swap brakes and axles into the 8 3/4? Been there done that, made no difference after all that time and money. Not me, never in a million years. And I'm not a numbers matching guy.
           
        • 448Scamp

          448Scamp Running Free

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          I would never use a spool mount again. They are all hype and no real advantage unless you are dragging the sway bar off.
           
        • Dohc Rocks

          Dohc Rocks Member

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          Lotsa great debate here.
          I'm just looking to build the best Duster I can from the factory parts bins.
           
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