1. NorcalGolddust

    NorcalGolddust Active Member

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    Working on swapping a 69 B body 8.75 into my 72 duster when I came across a problem. I centered the axle housing using the outside of the frame rail to the backing plate when I realized I had 1" gap between the string "frame" on the driver side but the passenger side would be flush, string sits smooth against the leaf spring. This also causes the tires to be offset 1" to the passenger side. Is this normal? The car shows no signs of damage or previous accidents. I get 42" from center to center on the leafsprings and they are parallel (measured front, middle, rear) with Doc Diff offset hangers. Not sure if i should center it to the frame or to the leaf springs, nothing's welded yet. And yes the offset shakes are installed correctly

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  2. NorcalGolddust

    NorcalGolddust Active Member

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    If I center axle to leaf springs, outer frame rail to outside rim is equal on both sides at approx 14"
     
  3. Dana67Dart

    Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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    To check for frame squareness do a cross measurement.
     
  4. MOPAROFFICIAL

    MOPAROFFICIAL FABO Gold Member FABO Gold Member

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    you're spreading the springs to fit it...right?
     
  5. NorcalGolddust

    NorcalGolddust Active Member

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    No. I cut off the old spring perches as I am using Doctor Diffs 1/2" offset shackles which put me at 42" center to center. I'm pretty sure I'm supposed to center the rear end to the leaf springs as that's how the old 7 1/4" rear end and leaf springs were. It's just the 1" frame offset to the pass. side is throwing me off
    Spring perch widths (center-to-center)
    A-BODY
    • '66-73= 43"
    B-BODY
    • '62-'70= 44"
     
  6. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    This should tell you what you need to know- you missed something the first time with your measurement. If the frame was offset, you'd get unequal numbers for that measurement- think about it.

    The perches need to be centered on the axle. Forget about where the springs and frame are. The springs can move on the bushings (some morons don't even move their perches when they install B-body rears on A-body's), the frame might not be straight, and pretty much every other body measurement has at least a 1/4" or more of tolerance from the factory. It's pretty common for the measurements not to be identical side to side if you're measuring to the wheel tubs or quarters. The axle housing has tighter tolerances on its measurements than anything on the body of the car.

    8 3/4's are centered, equal length axle shafts. So the perch-to-housing end measurement should be the same on both sides. Your '69 B-body axle is 60 1/8" end to end. You need 42" c-c on the perches with 1/2" offset shackles. A little math and you get 9-1/16" for the center of the perch to the outside of the housing flange. Or knock off half the width of the perch for 7-13/16" from the outside of the perch to the end of the housing. Make the measurements on the axle right, the rest will work itself out. Or not, but at least the axle will be straight.

    Keep in mind too that not all the backing plates for these cars have the same offset. If you don't know the history on that B-body rear, or if the brakes aren't complete or in working order, it's possible the backing plates don't match side to side. Another reason not to use the backing plates for measurements.
     
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    • I8NEMO

      I8NEMO FABO Gold Member FABO Gold Member

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      Definitely center your axle on the springs. Perches must be equidistant from center of axle housing. All other considerations are secondary. I feel your pain to a degree, after mini tub, spring relocation, and diff shortening I found a 3/8" difference between left and right fender which was not in the mini tub work but actually in the distance between frame rail and outer edge of fender lip. Had I known this was typical for the era, I could have accounted for a portion of this by shortening the rear less on each side.
       
    • Oldmanmopar

      Oldmanmopar Going left turning right FABO Gold Member

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      I have done many mini tubs, front clips, floors, torque boxes, Pinion angles, ETC. During all my years I have only found one A-body car that the front spring perches were not at an angle. These bodies were so different from one to another in all different areas. We have plates to slip in front of the front spring hangers to make them launch straight.

      Did you ever watch the burn out contests at Carlisile. Most of the car want to spin in a circle. Or at the water box at a track you always have guys holding them straight. Once you mini tub a car and permantly weld the boxes in what you have is what you get if you follow the factory mounting. My suggestion is to get the car to leave straight with shims with the factory hangers. Then Mini tub the car off of those measurements. My Duster took 3/8 's back on the passenger side. Then we moved the whole rear back 3/4 to lengthen the wheel base.

      I mentioned in another post I bought something over the weekend. I bought the frame rack used to calibrate and check frames from Mario Andretti's old race car shop. We'll be bringing it home next Sunday.

      I have several 108 and 111 mopar race cars coming that need to be corrected. This is going to make it so much easier. I have a new 108 body we will mount and make fixtures . That way we can just put a car on and make it bolt up so its correct.

      This being said. The distance of the perches should be the same from each end of the housing. Make the rear square and centered under the body. Install every thing loose. You will see you can move it around . The holes in the body are bigger then the studs and can always be oval ed same for the rear bolt on hangers. . The body is the frame on a uni-body car. The frame is just a strong fixture to mount things to Here are some measurements to go by. Add 3 inches for all measurements beteen the front and rear frame rails. This diagram is for a 108 wheel base cars. Barracuda, Duster, Demon, Dart Sport, 4 Dr. Valiants and Darts .. The Swingers ,Scamps, GTS's , Dart GT's are 111 inch wheel base

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      Last edited: Oct 26, 2019
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      • NorcalGolddust

        NorcalGolddust Active Member

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        Thanks everyone! I think between trying to rush b4 california and the electric company shut my power off and it being midnight I was starting to think in circles! Espo 6 leaf +1" and rcd bilstien shocks (thanks pst!)sure are an improvement over worn slant 6 leafs and midas shocks.... now I just gotta save for matching front shocks and larger torsion bars!

        20191030_173835.jpg
         
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        • NorcalGolddust

          NorcalGolddust Active Member

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          Side shot for those wondering about the +1 springs

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        • 67Baccaruda

          67Baccaruda Well-Known Member

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          I used the 1+ springs. Big mistake on my car, waited several years for them to settle. They didn't.
          I ended up taking them to a spring shop and having them de-arched slightly. Car sits a lot better now
           
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