Time to position the axles.
The front spring hanger on this trailer is 90" from the front. You can weld this front hanger in position now. The other 4 hangers will follow the front hanger position. Regardless what you have heard, there is not a calculation for positioning axles on a frame. This trailer will have a heavy front gate off one side, so I had to take that into account. In general, I like to have the front axle about 1/2 to1' back from center. This way I can put tires on the front axle only and move it around the shop with ease. The trailer is only slightly tongue heavy at this time.
If you notice the spring bolts, you can see they are shoulder bolts. This is to prevent the bolts from being over tightened. I don't like using these, but they do serve a purpose. Years ago I over tightened a bolt on the shackle end. The bolts were so tight, the spring could not flex. It actually ripped the hanger off the bottom of the trailer frame. I was left with a 2" x 4" hole in the frame that had to be repaired.
These equalizers are a pain at times to get assembled. The extra weight of the braked axle makes the equalizer pivot. I solve this by replacing the shoulder bolt with one of my standard trailer bolt. I can now tighten up the pivot point so the equalizer can not move. Finish assembling your bolts and links. Adjust the rear axle and equalizer hanger so the links are hanging straght down. Do this on both sides and measure the position of both side hangers. as long as you are withing a 1/4" you are good to go. Weld all the hangers in place. I don't weld all 4 sides of the hangers, just the front and back. I have found if you have 4" of welds on both sides, you can warp the frame upwards. The welds cool and shrinks the metal, especially if you have 3 hangers.
Tighten up the rest of the bolts and don't forget to loosen the pivolt bolt on the equalizer. 1-2 turns on the nut is fine.
You will notice on one of the pics that there is a gap between bolt head and hanger. Because of these shoulder bolts, this is as tight as you can get them. To me it looks like I forgot to tighten the bolts.
KO