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Discussion Starter #1
Hi all, I'm getting ready to install through-floor subframe connectors and Detroit Speed's HD front leaf spring pocket kit in my 1970 Nova. My best friend and his dad back-halfed a Fairmont years ago, and it went straight as a string from the first hit. He’s helping me… or maybe I’m helping him? Anyway, we took diagonal measurements from the front spring pocket mount bolts to the rear mount bolts of the front subframe, and they were about 1/4” different. I’ve been thinking about it, and I suspect we should have measured to a couple of the front suspension mounting points instead because the subframe can be moved around relative to the body, which is what locates the subframe mounting bolts. Am I on the right track?
 

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Drop a plumb bob down from a couple spots on the rockers where they clamp the body during production (holes in the rockers). Find the centerline of the car, then measure down from the ball joints and rear of the crossmember. See where everything lines up and move as necessary to get it all squared up.
 

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See if you can find this drawing for a 1970. I used one like this for our 69 camaro to measure off the factory assembly line mounting points. As already said, I dropped a plumb bob to the floor from the alignment pin holes and marked the floor and measured off the marks.
(hint: drill a hole thru a red wire nut and run the plumb bob string thru it. Then use the wire nut to center the string in the factory alignment hole.)
67412
 

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Discussion Starter #4
Thanks. Do I assume correctly that the alignment hole is the reinforced oblong hole near the front of the rear frame?
 

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I found on our camaro that one side has a round hole and the other is oval hole running sideways, I guess for giving the factory some leeway side to side. I used the round hole as the starting point. I believe these holes were for the alignment pins were on the body/chassis assembly line. When we installed the front frame we used alignment pins thru both front frame holes and measured before tightening the frame up and welding in the frame connectors and 12 point cage in.

FYI that picture I posted is for a 1976 Nova. I didn't find the one for a 1970 with my quick search it was just for a reference. These are used by body shops for frame straightening.
 

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Discussion Starter #7
Interesting. Just going by memory, mine are both longer front to back. I'll see if I can find the frame diagram for a 68-72 Nova. If not, I guess I'll just go for equal measurements side to side.
 

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I found this.

 

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68-72 were a little hard to find, so make sure that one is the correct one.

When I did ours i dropped a bunch of points to the floor with a plumb bob and then connected them with snapped chalk lines then I sprayed clear paint over them so they didn't get sweeped up.. And by a bunch i mean almost every reference point under the car including the stock rocker boxes. I did a complete back half so i wanted as many points as i could get.

Have fun on your project.
 

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Discussion Starter #11
Well, we did a bunch of measuring yesterday evening, and the car is surprisingly straight from the front of the rear subframe forward. The diagonal measurements for the rear subframe are about 1/4" different, but I think we can compensate for that with the slop in the front leaf spring mounts and shuffling thick and thin thrust washers around at the shackle mounts.

I gotta say that using a dot/plumb laser makes this job SO much easier than using plumb bobs. My best friend has one for work, but if he didn't I would definitely pay $100 for a simple one even if I didn't think I'd ever measure another chassis.
 
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