Choosing a rear suspension

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Thejames6972

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Hey everybody! Seeking help and advice for a rear suspension set up. Car is a 71 duster, Inboarded springs and narrowed 8 3/4. Engine is a 421; half filled block, 3.5” stroke, 4.380 bore, 14.5-1 compression with b1-bs heads. Plan to run e85 and maybe a single stage of juice. Trans is a th400 with a brake. Car will be a grudge car and see the track only. No street driving. Problem is I can’t decide on a rear suspension set up for this car... I’ve debated on running SS springs but am not sure if I would be overpowering them and if they would hook. I’ve read allot about caltracks and split monos and it seems to be a mixed review on them as far as a- body mopars go. My goal for the car would be to dip into the 9s. Any insight, advice, or help would be greatly appreciated!
 
CalTrac's come to mind. Let us know how it all works out.
 
Sorry, didn't see your mention of the Caltrac system. My bad....
 
It’s alright, caltracs are a consideration but I’d rather spend my money on something that is proven to work rather than something I’m hearing mixed reviews about. I do understand you can’t just bolt them on out of the box and expect them to work, I don’t mind spending time tuning my suspension properly and learning the ins and outs of whatever ends up going on the car.
 
There is a set of Asassin bars for sale here on FABO. That's what I'd spend my money on. Way more adjustable than a cal trac bar.

That and double adjustable shocks on all four corners and you should hook in a car wash.
 
IIRC, even in the MoPar books, getting into the 9’s, they recommended something else besides the SS springs. IIRC, 4 link came to mind. These writings are before. Al Tracks or Assassin bars came out.

I have a few buddies (in the past) run high 9’s on S/S springs. Over powering the spring is easy on 13 second cars if nothing else is addressed. SS springs aren’t magic springs. Just part of the equation.

How heavy is the car?
Car Weight Distribution is????
Over all weight?
Are the rear clamps still holding the springs together?
Are the front clamped?
Extra clamps?
How much tire do you have?
Did you make sure the rear shackle is properly placed allowing movement properly?
You can also use sliders in there place. (Shackles)
SHOCKS!!! A major roll ignored.
How hard is your hit?
This is also a problem no matter what set up you have. I say this because the best OOTB set ups aren’t looked at, just installed and raced. I know if you guys that have opened up the box, installed the part, went racing. And then they wonder why they did I wheel stand, why didn’t I wheel stand, why do I go right/left, they get swirly down the other end, etc....I myself would use the assassins and a split mono weeks for the cars weight. If you’re moving away from that, then you might want to look into something a bit more exotic than SS springs.
Like a 4 link.

Have fun and good luck!
 
I'd look at parallel 4 link with a panhard to keep the rear centered along with adjustable shocks on all corners, course the rear would be a coil over shock but This would allow you to fine tune the suspension to not only hook but hook straight. Plus you'll likely save a few pounds over the super stock leaf set up. Not much but a couple. With the power level you're looking at to dip into the 9s, I think you're best bet is the 4 link.
 
dukeboy_318 said:
I'd look at parallel 4 link with a panhard to keep the rear centered along with adjustable shocks on all corners, course the rear would be a coil over shock but This would allow you to fine tune the suspension to not only hook but hook straight. Plus you'll likely save a few pounds over the super stock leaf set up. Not much but a couple. With the power level you're looking at to dip into the 9s, I think you're best bet is the 4 link.
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Ummm, like a QA1 set up?

70aarcuda said:
sell the 8 3/4....and buy a dana 60
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Or a Ford 9.
True, it’s just a matter of time. Shorter if the car is heavy. Even less time with a manual trans.
 
PLENTY of cars run the SS springs in the 9s. Jes sayin.
 
rumblefish360 said:
Ummm, like a QA1 set up?
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Sure or a Control Freak parallel or even the Gerst parallel, though it runs a watts bar and is more suited to road racing but would work nevertheless. When it comes to 4 links, I'm just not a big fan of triangulated 4 links and prefer the parallel
 
fishmens67 said:
4 link and be done.
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With a manual trans, it is suggested to move away from SS springs. At a certain point. At 9.50’s and quicker, they suggest something else besides SS springs.
As per the chassis book, but of course, this isn’t saying it can’t be done with leaf springs. I believe they think it better and easier to go away from the SS springs at a certain point. And while probably true, your wallet may argue or you may just want to try the springs anyway.

902ED843-8C39-4C00-BB9A-FD295119961C.jpeg
 
rumblefish360 said:
With a manual trans, it is suggested to move away from SS springs. At a certain point. At 9.50’s and quicker, they suggest something else besides SS springs.
As per the chassis book, but of course, this isn’t saying it can’t be done with leaf springs. I believe they think it better and easier to go away from the SS springs at a certain point. And while probably true, your wallet may argue or you may just want to try the springs anyway.

View attachment 1715126141
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Actually by the time you add up the cost of SS springs, shocks and the other upgrades such as extra clamps, shackles etc, it's not much more these days to just jump into a 4 link, granted there's much more work involved.
 
dukeboy_318 said:
Actually by the time you add up the cost of SS springs, shocks and the other upgrades such as extra clamps, shackles etc, it's not much more these days to just jump into a 4 link, granted there's much more work involved.
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Oh hell no and no way.
1 example ... GTS Rear Suspension | Gerst Tubular Suspensions

4-Link MOPAR Coil-Over Rear Suspension Systems

Rear Suspension

There is no way SS springs, shocks, shackles and even off set hangers, perch welding is this expensive.
 
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Verse springs @ $2-4 each which is incredibly expensive since Fiat took over and stopped making stuff. You could go to springs and things (espo.com) and pay about half.
1971 DODGE DART Stock Height Springs - Leaf Spring Type

And again some incredibly expensive Mopar parts which can be purchased a lot cheaper
1971 DODGE DART Mopar Performance Straight Shackle Kits P5249715


Your shock purchase price is on you but included with the “kits” above as well as the other parts.

You would reuse the front spring hangers.
 
LOL, well the SS springs are probably no longer being made since Fiat took over. I’m sure they’ll go up in cost! The A body springs cost was silly.

Reasonably priced replacement springs I got from espo.com (Springs and Things)
I ordered them in a 1 inch overbend 6 leafs each side. Launched straight as an arrow. Road great.
Made in Pennsylvania!
 
Thanks for all of input guys! Was kicking around the idea of 4 link or ladder bars but I figured if I was to go that far with the fabrication I might as well back half it and that’s not exactly in the budget at the moment...I don’t know how much the car weighs, or any details like that because it’s never been put together. Just looking for a good starting point. If the chassis bible says you can run SS springs to 9.50s I may start out there just to see how it performs on them being that they can be had for $225 near me. I am however going to invest in nice shocks all the way around as you guys suggest. If the SS springs don’t work out I can always go to caltracs or assassins and be one step ahead already having nice shocks all the way around.
 
Looking thru Summit Racing.....I ran across Mopar Performance Super Stock Springs for $265 a set....delivered to your door. For those who are gonna street drive it (not you) , simply buy the same spring with same arch for both sides (@$132ea)....the car will sit level.

In stock....readily available. Real deal..not knock offs.
 
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It is IMO that a good move would be to relocate the springs inboard for max tire width. (Which I suppose you know about and your doing.) Look into “Viking” shocks on all 4 corners. Users seem to love them. Sorry, no practical experience with them.

There is a reason SS springs are the way they are and not 1 spring for both sides.
 
rumblefish360 said:
It is IMO that a good move would be to relocate the springs inboard for max tire width. (Which I suppose you know about and your doing.) Look into “Viking” shocks on all 4 corners. Users seem to love them. Sorry, no practical experience with them.

There is a reason SS springs are the way they are and not 1 spring for both sides.
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Yessir, I have already done the spring relocation into the frame rails along with a mini tub.
 
Excellent. Your well on your way then.
 
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