66 4x4 my sons new project

[argonaut]

Ah, okay, now I remember how I decided the relative vertical position of the hangers!

First I mounted the shackle hanger in the rear. It aligns horizonataly with the mounting position of the old shackle hanger. However there isn't much of an option, you pretty much have to mount it so that the bolt holes are centered between the top and bottom of the frame (same as on the donor truck). I then took some measurements and figured the effective drop of the rear spring eye, compared to stock, given this new shackle hanger location, and the longer shackles. I think it was around 4-5" lower.

Second I dropped a plumb bob at the location for the stock front hanger eye bolt. Then I positioned the front spring hanger with its eye bolt location about 5" lower, and rotated the bracket so that it was effectively oriented perpendicularly to the bottom of flange of the frame (since the frame is sloped and tapered in this area. This was necessary so that the backing bracket would sit flush with the under side of the frame flange and bolt together with the frame crossmember.

This resulted in spring geometry similar to the stock geometry, but without using the huge 5-1/2" stock lift block, and with a longer shackle. If I remember correctly I also lowered the front of the spring a little more than the rear, as this gave me a spring angle more similar to the newer model trucks I was using for reference. My logic was that the newer trucks probably handled heavy loads a little better and rode a little more comfortably, and thus some engineer had determined a more optimal rear spring and shackle design to accomplish this. Hopefully it works out!