I was never a fan of the way the mono leaf perch locates the rear on the springs. It uses the lower shock plate to locate, as opposed to the multi-leaf system which uses a pin on the top of the spring that locates in the hole in the spring perch. Here's what I did to put a 3 leaf spring plus a lowering block into a mono perch:
- I bought 2 grade 8 socket head capscrews (aka Allen head bolts) and replaced the bolt that clamps the leafs together. The head of the bolt is now the locating pin. If you already have that type of bolt in your springs, you can skip this step.
- I went to the hardware store and bought a length of 1/4" x 2 1/2" flat bar steel, and cut two identical pieces to fit in each spring perch. Roughhly 5 1/2" as I recall.
- I measured the diameter of the Allen head bolt with a caliper.
- I marked the center of of the pieces of flat bar by drawing diagonal lines corner to corner. The intersection in the middle is center.
- I drilled a hole in piece of flatbar that matched the diameter of the bolt head using a Christmas tree bit.
- With the rear out of the car on horses, I bolted one of the lower shock plates to a perch. Slid the flat bar into the perch and used the large hole in the center of the lower shock plate as a guide to center the hole in the flat bar in the exact center of the perch. Stuck the bolt head in the hole, and made a bushing out of an aluminum spacer I had laying around just to make sure it was lined up perfectly.
- Once I was certain the flat bar was perfectly located in the center of the perch, I welded the flat bar to the perch. Repeat on the other perch.
- I set the lowering block on top of the spring (hole already drilled in center of it) and used the allen head bolt to bolt the block and springs together.
- Install rear back into car. The allen head bolt locates the rear positively in the perch and is pretty much fool proof.
There will be a fairly good sized gap between the bottom of the perch and the shock plate. I chose to fill in the gap. I used some square tubing with holes drilled for the U-bolts to pass through. I used U-bolts at all four locations.
It sounds complicated, but it's pretty easy.
Note the absence of rubber pads.