The info on this forum is second to none! With that said I need some insight from some people familiar with the install of super stock springs (70 dart). We removed an 8 3/4 rear, relocated the springs inboard 3" and replaced the stock springs with super stock springs. We had a Dana 60 shortened slightly and the new perches appropriately moved in as well. This was done at a very competent street rod fab shop. The problem is the perches seem to contact the springs differently. If you lightly cinch down the driver side perch the passenger side will be lifted about 3/8" in the rear. (as if the pads where welded at 2 different angles). The pads appear to be welded the same and owner/fabricator states that they must be identical due to the bench and jig that he uses. I do believe they are the same, so question is... due to the fact that the super stock spring is a different stack design side to side, does that cause a different arch drastic enough to cause this "problem"? And if that is normal is it correct to just cinch down the other side and not worry, or should the other pad be welded to match the springs curve? Am I just over thinking this?
Don't know much about new stuff, but the old Mopar SS springs were a lot different side to side. There was a right and a left. The springs made the car sit way off level when parked, but the car would twist to a level stance under maximum acceleration. Every one I knew who used them ran standard spring pads on the axle, but wedge shims were available to "tune" the suspension to some degree by adding more wedge. These were never intended for street use, and I cannot imagine that they would be used on modern day race cars. With all the suspension science and development of the last 40 years I have to ask why would you use them? Yes, the situation you have described is normal for these springs.
Old school technology, but effective from what we have seen so far. Alot cheaper then the 4 link set up too.
Yup, one side will sit higher than the other. The super stock springs don't have the same number of leafs, or the same arch, from side to side. The difference in arch is clearly visible even if you just set the springs next to each other. If its only 3/8" higher then you got lucky, most of them are even more noticeable than that.
Take a close look at the spring stack and youll see they are different left to right. Ran these same springs in a 68 camaro back then. They bolt in with washers to shim the width difference, they are narrower than chevys spring. Fooled a lot of racers running a leaf spring camaro with no slapper bars. One racer, at beautiful US 30 in Gary, studied our car on the trailer, went home and took his traction bars off, and showed up next weekend. Dropped the clutch[a 9 second car] and the rear end twisted so bad it destroyed the floor pan of his s/s camaro.
To be clear... The 3/8" is the gap at the back of the perch with the other side cinched flush. I do realize that the two springs are different, but that gap at the perch seems odd. Wouldn't that create a unwanted preload on the spring when tightened?
If you want precision you need to tack the perches with the rear axle in the car and sitting on the springs, then remove and finish weld. Precision was not expected in 1970 auto manufacturing and the SS springs are not manufactured to be precise either. Combine that with a unit body Mopar that's been driven hard for 42 years, you'd have to be lucky to have everything line up. The real test is does the car launch straight, but even then uneven traction side to side or not level pavement can screw that up. I run into the same thing anytime I add a rear anti sway bar to the rear of any leaf spring car. The two sides never line up and have to be shimmed to not preload the springs. If it keeps you up at night add some of the wedge shaped pinion angle correction shims so there is no preload on the springs. It's science, but it ain't rocket science.
Good luck. I already laid it out for him. That was when he started asking about "unwanted preload". Then we get another Einstien on here, telling him how to mickey mouse the installation to negate the preload Chrysler spent time engineering into the springs. These guys are WAY to smart for me. At this point, I say, let him go ahead. In a month he will post another thread. "Why does my car head for the tower side guardrail every time I launch?"
Some thing about all this reminds me of why I quit drag racing. I quit right after I caught a feller dropping a hand full of pennies and dimes down my carb. He went home with a fine Alabama ass whuppin, and I got banned from the track for life.
I recommend closely checking the axle perches to see if they are parallel. Use two long straightedges on the perches with the axle out of the car and see if they are parallel. Even pro shops can screw things up. 3/8" is a huge gap over the short length of an axle perch. If the axle perches are right on, then look into the leaf spring mount locations (they were modified, too) and finally the springs themselves. I remember hearing (rumors?) that the recent SS springs are not as good as the earlier DC ones. Agreed that this is a 42 year old car, but the rear suspension is much newer. Now is the time to make it right so it doesn't want to change lanes of smack the guardrail.
The purpose of this post was to get a useful response to the question of the perch to spring relationship that was described. I value the insight that comes from experience. I am not putting down or disregarding the answers... I am just trying to understand if this is correct. As pointed out by 30dodgeboy quality is not something commonly found anymore. Please understand that the opinions whether correct/partially correct/ or incorrect are still valid to learning. thanks
s.s. springs are different side to side. they both should have part numbers on them. one will end in an odd number, the other an even. the lower of the two numbers is the right spring. it will look funny pulling them tight. mainly because of the amounts and lengths of the leaves from side to side. i would get everything snug, set it on the wheels. and than tighten everything. remember the u-bolts only get about 70 ft/lbs. yes you should have the perches loose and weld them last. but i have done it both ways. check the pinion angle. you want 5-7 degrees.
As several have already mentioned, the springs are different left and right by design. One thing I would have your shop double check is that the perches are square on the housing. I run into this problem every day with customers we sell Cal-Tracs and split monoleaf springs to.
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