Bruzilla
Well-Known Member
I wanted to replace the stock 74 springs on my 74 Roadrunner with a set of Mopar Performance super stock springs. Of course like with so many other things, 73+ cars are a little bit different than their predecessors. When it comes to leaf springs, 73+ cars have the rubber isolated mounts for the leaf springs.
Pre-72 cars use mounts and shock plates with a small 3/8" hole for the stud and nut on the springs. The 73+ cars have a 1" hole that allows a rubber doughnut to fit into them, and then there's a 1/2" spacer that goes inside the center of the stud and threads onto a 3/8" bolt that ties the top of the isolator to the bottom.
Here are some pictures of the isolator top (on the top) and bottom (on the bottom):
I had to admit the rubber was in excellent shape for being 40 years old. The inner surfaces looked nearly new and there was no cracking or dry rot.
I looked at the super stock springs and noticed the stud that runs through and fits into the holes in the pads and shock plate is 5/16", so it's a bit smaller than the OEM bolts. Here is a picture of the two bolts. OEM is on the top and super stock is on the bottom:
I decided to try to make a 5/16th's version of the OEM bolt. I went to Lowes, got some 4" long 5/16th's grade 8 bolts, five washers, and some nuts. I got an old 9/16th's nut/washer combo out and used it along with the four washers to make an end that looked like the 5/16th's OEM end as seen below:
I reattached the upper and lower isolators using the 5/16th's inch version, and they went on just fine. I just needed a D clamp to compress the springs back together until I got the nut on and tightened down. I think the bold need to be 3.5" long, so I'll be cutting off the extra 1/2", but it did make it easier to install the isolator, so I would suggest using 4" and then cutting them rather that using a 3.5" bolt.
And here's the isolator affixed to the super stock spring:
Pre-72 cars use mounts and shock plates with a small 3/8" hole for the stud and nut on the springs. The 73+ cars have a 1" hole that allows a rubber doughnut to fit into them, and then there's a 1/2" spacer that goes inside the center of the stud and threads onto a 3/8" bolt that ties the top of the isolator to the bottom.
Here are some pictures of the isolator top (on the top) and bottom (on the bottom):
I had to admit the rubber was in excellent shape for being 40 years old. The inner surfaces looked nearly new and there was no cracking or dry rot.
I looked at the super stock springs and noticed the stud that runs through and fits into the holes in the pads and shock plate is 5/16", so it's a bit smaller than the OEM bolts. Here is a picture of the two bolts. OEM is on the top and super stock is on the bottom:
I decided to try to make a 5/16th's version of the OEM bolt. I went to Lowes, got some 4" long 5/16th's grade 8 bolts, five washers, and some nuts. I got an old 9/16th's nut/washer combo out and used it along with the four washers to make an end that looked like the 5/16th's OEM end as seen below:
I reattached the upper and lower isolators using the 5/16th's inch version, and they went on just fine. I just needed a D clamp to compress the springs back together until I got the nut on and tightened down. I think the bold need to be 3.5" long, so I'll be cutting off the extra 1/2", but it did make it easier to install the isolator, so I would suggest using 4" and then cutting them rather that using a 3.5" bolt.
And here's the isolator affixed to the super stock spring:
