8 3/4 swap

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Infiniti Dave

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Hope for advice from other Mopar Lovers. While attempting a rear axle upgrade from an 8 1/4 to an 8 3/4 I discovered a broken R/R spring on my 79 Aspen RT. (I know it's not an "A" body , but it's what my current project is.)Didn't really think much of it , so I ordered new Direct Connection Superstock springs from my local Summit Store. Part numbers are 3412003 and 3412002. Found out 3 months later that the replacement spring hangers part number DCC-P4120105 were no longer in production and not available. Found what I thought was a viable solution from Mancini . Part number AR110. Trying to assemble everything doesn't work since nothing lines up. Even the spring center bolt looks wrong. I can't help but think I'm not seeing something obvious ! I appreciate any and all advice. THANKS!!!
 
ive seen front spring hangers for sale that allow you to pt e body leaf srings in an FMJ

maybe your problem is why that exists. im not sure.
 
Nothing about that swap is going to line up until you step away, take a deep breath, and form a plan.
First off, F/M/J bodies use an oddball "Iso-Clamp" spring perch and mounting hardware, which will not fit an 8.75 without a lot of unnecessary work.
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Image is from the FMJbodies only site. It shows the Iso hardware in red, compared to standard Chrysler hardware in blue.
Since you're going to run SS springs, just trashcan all the Iso stuff and replace it with standard Chrysler shock plates and U bolts. This will also alllow you to run B body rear shocks instead of the increasingly hard to find FMJ units.
Now for your front spring hangers- you got the AR110. Those are to run E body springs on an FMJ. You have SS springs which are A body sized. E body springs have a 22" front segment, A body has a 20" front segment. So if you use those you'll be moving your axle two inches forward- not good. You need hangers that are another 2" longer than the ones you got; I'm not aware of any currently available so you're probably going to have to fab them yourself (along with the rear shackle mount).
You really need to go over to the ForFMJBodiesOnly site or Dippy.org and do some searching and reading- this is a common swap so info is readily available.
 
Thankyou to all for your help. The information from professor fate struck several chords as I've already purchased 8 3/4 hardware and shock mounts as well as "B" body shocks. The axle moving 2" forward looks like exactly what I have. Thought the extended front spring mount would solve that , but I guess not. Will look up the other mentioned web sight. Again my sincere thanks.
 
Infiniti Dave said:
Thought the extended front spring mount would solve that , but I guess not.
Click to expand...
Your thoughts are correct- it's just not extended enough, since it's intended for E body springs and not A body springs.
Best bet at this point is either make your own brackets with the correct dimension for your spring (and box it/reinforce it well, it's getting pretty long at this point) or trade your SS springs for a set of E body springs and use the front hangers you already have.
 
Fortunately you just answered my next question. The thought came to me that using "E" body springs might be the easiest solution. Any thoughts about the rear shackles ? Again thankyou for all your help and solutions !
 
If you want a pair of FM&J hangers, contact Bridger Bollinger on the FM&J site. He has at least 5-6 Aspen/Volare bodies at his place. If he doesn't respond back, let me know and I'll PM you his number.
 
Infiniti Dave said:
Fortunately you just answered my next question. The thought came to me that using "E" body springs might be the easiest solution. Any thoughts about the rear shackles ? Again thankyou for all your help and solutions !
Click to expand...
I think you might be okay with the stock rear shackle mount- the E body spring with your front hanger will put the rear spring eye about 1" further to the rear from where the F body spring was, which I don't *think* should cause any issues in this case.
I haven't worked on an F body in a number of years, so I don't recall exactly what would be involved in moving the shackle mount back 1", but it's worth a look while you're under there...
 
I have the "FMJ" front hangers from Mancini. Hangers look okay , but the springs are still too short and the center bolt to locate the axle is too far forward. I'm thinking the DC springs are the fitment problem. Thanks for the help and advice.
 
Have you thought about having your original springs re-arched, and maybe have a leaf added?
 
Thankyou Professor for all the help and advice. I think your suggestion about using my current hardware with "E" body springs will likely solve the problem.
 
These replies aren't in the right order , but here goes to "Demonracer. Repairing the spring didn't seem like an option since the front mount "hook" was broken.
 
Okay, contact the guy I mentioned on the FM&J site. better yet, I have a friend who went to a coil over rear suspension and may still have the springs he took out. The springs were in a 79 Road Runner 360 car. I will contact him if you would like me too.
 
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