I'm correcting you not to prove a point, but to keep others from being misinformed when they find this thread in the future using that handy dandy search function.
***For the following example we will ignore the fact that the spring has an arch and does slightly grow/shrink the front eye to center pin measurement as it compresses/droops.***
Think of your axle as two halves. Your axle is located with the fixed half of the spring, in this case the front half. For a stock GM 73-91 frontend spring the axle is always located 23.5" from the front eye at ride height. This means the rear 'floating half' (for lack of a better term) of the spring can be long or short and it will not affect your axle location. The shackle angle will be the only effect of a longer or shorter rear spring half.
Now onto the modifications that actually moved your axle forward:
+4.0" Note 1
+1.5" Note 2
- 1.5" Note 3
+4.0" Total the axle moved forward
Note 1: Front spring eye mount moved forward 4". This netted you an honest 4" forward because you moved the fixed mount of the spring forward.
Note 2: Zero Rates moved the centerpin 1.5", effectively decreasing the distance from the pin to the front fixed mount.
Note 3: Stock GM front springs are 23.5" for the front eye to pin measurement. Ford 57's are 25" for this same measurement. Therefore, the Ford springs effectively moved the axle 1.5" FARTHER from the front fixed mount.
All this can be easily demonstrated with a tape measure, your vehicle, and another vehicle with the exact same frame. Find a common landmark on both frames like an identical factory hole. Measure to the axle tube on each vehicle from this same hole. The difference between the two vehicles will be much closer to 4" than 9.75".
Travis
***For the following example we will ignore the fact that the spring has an arch and does slightly grow/shrink the front eye to center pin measurement as it compresses/droops.***
Think of your axle as two halves. Your axle is located with the fixed half of the spring, in this case the front half. For a stock GM 73-91 frontend spring the axle is always located 23.5" from the front eye at ride height. This means the rear 'floating half' (for lack of a better term) of the spring can be long or short and it will not affect your axle location. The shackle angle will be the only effect of a longer or shorter rear spring half.
Now onto the modifications that actually moved your axle forward:
+4.0" Note 1
+1.5" Note 2
- 1.5" Note 3
+4.0" Total the axle moved forward
Note 1: Front spring eye mount moved forward 4". This netted you an honest 4" forward because you moved the fixed mount of the spring forward.
Note 2: Zero Rates moved the centerpin 1.5", effectively decreasing the distance from the pin to the front fixed mount.
Note 3: Stock GM front springs are 23.5" for the front eye to pin measurement. Ford 57's are 25" for this same measurement. Therefore, the Ford springs effectively moved the axle 1.5" FARTHER from the front fixed mount.
All this can be easily demonstrated with a tape measure, your vehicle, and another vehicle with the exact same frame. Find a common landmark on both frames like an identical factory hole. Measure to the axle tube on each vehicle from this same hole. The difference between the two vehicles will be much closer to 4" than 9.75".
Travis
its a good thread
