Everytime I use lowering blocks I manage to crack one. They have always been a temporary fix to see where the car will sit though. I learned this from my friend John 4 years ago and this is my second time doing this. The benefit is getting the car lowered, stiffening up the rear, and not having to worry about cheap cast aluminum lowering blocks breaking. The list below is as detailed as possible, it is cheap and quite simple.
What you will need:
2 pairs of leaf springs
(1)5/16"x60" allthread
(5) 5/16 nuts that fit the allthread
(2) 2.5" 5/16 allen head bolts
(2) 5/16 lock nuts for the allen bolts above
(3) 5/16 flat washers
(4) 2.5" or 3" squared U bolts with
-these should fit on top of the leafs without binding
-threads should go up enough to clamp tight onto the leafs
(4) flat plate steel strips with 2 holes on each end for the U-bolts
(8) washers the same size as your squared U bolts
(8) lock nuts the same size as your squared U bolts
Prop the car up on jackstands at the frame rails. remove the leaf springs and keep a jack under the rear end. You will have to loosen the U-bolts and the rear shock lower mount. It is possible to do this in the car but easier to remove the leaf springs. I pulled them apart down to the individual leafs. I number each leaf from shortest to longest, 1,2,3,4 on a 4 leaf set. Now, the leaf set I pulled from the Mustang, lets call set1. The extra set I had came from a 68 Cougar, set2. I used a hammer to knock the clamps sliding them close to the eyes on leaf 4. I removed the through bolt that centers each leaf and holds them together. Keeping set1 in order I placed, from set2, leafs 3 and 2 on top on a negative arch. A mental picture, the space between set1 and leafs 3/2 from set2 is a football shape. That's an American football for anyone outside the US. Set the leafs in its side. Now, take the length of allthread and lock up two nuts in the center on the rod. Run it through one of the 5/16 washers and then through the hole to center the leafs starting on the set1 leaf 1 all the way through the set2 leaf2. On the set2 leaf2 end place the washer and hand tighten one nut. On the opposite end on the allthread, lock up 2 nuts. For safety reasons I put the Squares U-bolts together loosly and place it inward on the leafset as possible to prevent the negative arched leafs from slipping off the set on either side. I used a workbench but this could easily be done one the ground. On the set2 leaf2 side I put a 1/2 box end wrench. On the other end I used an impact gun with a 1/2 socket. Keeping the 1/2 wrench braced I torqued the other end with the inpact gun intermitantly until the set was tight enough to fit in a vise, which isn't necessary but helps take tension off the allthread. As it tightens keep moving the squared U-bolts more inward for safety. In the vise I clampted down close to the center of the leafs then tightened with the impact gun some more, and kept doing that until there was no light between the leafs. It is just the same if you use the impact gun and wrench all the way down. Once tight, either clamp the vise tight as close to the allthread as possible. Or, w/o a vise use C clamps on both sides of alltherad. Once clamped down, using the same method to tighten in reverse, loosen the allthread and remove it. Replace it with 1 5/16 allen bolt and flat washer on the set2leaf2 side. You might need a hammer to carefully help it through the leafs. On the other end use 1 5/16 locknut. Try getting the squared U-bolts as close to where the original clamps were. I tightened them down to just where the top 2 leafs(set2leaf3,2) compress a little, and the U-bolt wont slide back and forth. The original clamps we left by the eyelets, I thry to get them over as many leafs as possilbe and hammer them towards the center. Repeat with the other side of set1. This is probably lower tham most like it. Results vary depending on arch, and wear on the leafs you use. If too low, try removing one of the set2 leafs. Removing the set2leaf2 will lift the car a little. Removing the set2leaf3 will lift it more. Unfortunately and regretfully I didn't take any before and after pics. To give an idea, with stock leafs and no blocks I had a 2" gap from the top of the tire tread to the rear fender lip on a 25" tall tire. After this mod using set2leafs3,2 I lowered aprox 3" with the tire tucked hiding the tread line on the sidewall inside the fenderwell. I think I have an old pic of what the car looked like before. I'll post later.
What you will need:
2 pairs of leaf springs
(1)5/16"x60" allthread
(5) 5/16 nuts that fit the allthread
(2) 2.5" 5/16 allen head bolts
(2) 5/16 lock nuts for the allen bolts above
(3) 5/16 flat washers
(4) 2.5" or 3" squared U bolts with
-these should fit on top of the leafs without binding
-threads should go up enough to clamp tight onto the leafs
(4) flat plate steel strips with 2 holes on each end for the U-bolts
(8) washers the same size as your squared U bolts
(8) lock nuts the same size as your squared U bolts
Prop the car up on jackstands at the frame rails. remove the leaf springs and keep a jack under the rear end. You will have to loosen the U-bolts and the rear shock lower mount. It is possible to do this in the car but easier to remove the leaf springs. I pulled them apart down to the individual leafs. I number each leaf from shortest to longest, 1,2,3,4 on a 4 leaf set. Now, the leaf set I pulled from the Mustang, lets call set1. The extra set I had came from a 68 Cougar, set2. I used a hammer to knock the clamps sliding them close to the eyes on leaf 4. I removed the through bolt that centers each leaf and holds them together. Keeping set1 in order I placed, from set2, leafs 3 and 2 on top on a negative arch. A mental picture, the space between set1 and leafs 3/2 from set2 is a football shape. That's an American football for anyone outside the US. Set the leafs in its side. Now, take the length of allthread and lock up two nuts in the center on the rod. Run it through one of the 5/16 washers and then through the hole to center the leafs starting on the set1 leaf 1 all the way through the set2 leaf2. On the set2 leaf2 end place the washer and hand tighten one nut. On the opposite end on the allthread, lock up 2 nuts. For safety reasons I put the Squares U-bolts together loosly and place it inward on the leafset as possible to prevent the negative arched leafs from slipping off the set on either side. I used a workbench but this could easily be done one the ground. On the set2 leaf2 side I put a 1/2 box end wrench. On the other end I used an impact gun with a 1/2 socket. Keeping the 1/2 wrench braced I torqued the other end with the inpact gun intermitantly until the set was tight enough to fit in a vise, which isn't necessary but helps take tension off the allthread. As it tightens keep moving the squared U-bolts more inward for safety. In the vise I clampted down close to the center of the leafs then tightened with the impact gun some more, and kept doing that until there was no light between the leafs. It is just the same if you use the impact gun and wrench all the way down. Once tight, either clamp the vise tight as close to the allthread as possible. Or, w/o a vise use C clamps on both sides of alltherad. Once clamped down, using the same method to tighten in reverse, loosen the allthread and remove it. Replace it with 1 5/16 allen bolt and flat washer on the set2leaf2 side. You might need a hammer to carefully help it through the leafs. On the other end use 1 5/16 locknut. Try getting the squared U-bolts as close to where the original clamps were. I tightened them down to just where the top 2 leafs(set2leaf3,2) compress a little, and the U-bolt wont slide back and forth. The original clamps we left by the eyelets, I thry to get them over as many leafs as possilbe and hammer them towards the center. Repeat with the other side of set1. This is probably lower tham most like it. Results vary depending on arch, and wear on the leafs you use. If too low, try removing one of the set2 leafs. Removing the set2leaf2 will lift the car a little. Removing the set2leaf3 will lift it more. Unfortunately and regretfully I didn't take any before and after pics. To give an idea, with stock leafs and no blocks I had a 2" gap from the top of the tire tread to the rear fender lip on a 25" tall tire. After this mod using set2leafs3,2 I lowered aprox 3" with the tire tucked hiding the tread line on the sidewall inside the fenderwell. I think I have an old pic of what the car looked like before. I'll post later.