Suspension/Chassis Suggestions - 70 Dart Swinger

[pyrogen007]

I have read through quite a few suspension threads and find myself more confused/undecided than when I started. I am looking for suggestions on how to proceed in regard to the suspension and chassis setup, the end goal is to have a sporty daily driver. Initially, just to get it running/driving I am installing an 80s truck 318 but I have a 2/3 complete 451 stroker with aluminum heads I might install later. I have some time to save up as I am still putting it back together but priority is getting this car running and driving and upgrading over time, I just need a solid plan on how to meet my goal, below is what I have:

Car info:
70 Dodge Dart Swinger 2 dr Hardtop
225 CI 6cyl - removed and sold
3 spd auto on column - removed, converting to 4 spd
7 1/4 rear axle
4 wheel drums


Suspension/Chassis Parts I have:
Refurbished factory 73+ UCAs, LCAs, strut rods, V8 K frame and disc brake spindles with Energy suspension's Poly Master kit
Stock replacement ball joints
Wilwood Dynalite Pro front disc brakes, 10.75" diameter vented rotors - 4.5" bolt pattern
6 cyl Torsion bars - still in the car
6 cyl Leaf springs - still in the car
8 3/4 housing w/ 489 sure grip center
axle shafts - 4.5" bolt pattern
10 or 11in drums, I believe I have both
Factory power steering gear box
Stock tie rod ends, adjusters, pitman arm and idler arm
Comp Engineering 3 way adjustable drag shocks - probably won't use these.


These are the parts that I believe that I need to purchase to increase the performance of the suspension to meet my goal, what would the priority be in order of greatest benefit first?

Torsion bars
Rear leaf springs
Shocks
Sway bars(front & rear)
Chassis stiffening
UCA upgrade
LCA upgrade
Ajustable/dynamic Strut rods
Delrin bushings
Wheels
Tires

The 6cyl suspension is still in the car because I have been working on the body and rebuilding the HVAC. The rebuilt stuff is not in the car yet so now is the time to weld in the reinforcements to the LCAs and K Frame I assume. I also assume that torsion bars, leaf springs and shocks should be installed at the same time as the front and rear axle assys, please correct me if I'm wrong.

Thanks for the help!!

 

[remytherat]

Sway bars and torsion bars will make the biggest difference. Good shocks should fit in somewhere too. If you plan on using the stock 73+ UCA, the moog offset bushings are a good caster upgrade.

 

[pyrogen007]

Good info, thanks for the reply! Is there a chart similar to the SKOSH chart sticky to help decide spring rates, tire/wheel sizes ect?

 

[Demonx2]

@72bluNblu

 

[michiganpat]

get 6 leaf HD springs for the back, front, I upgraded my 6 cyl to .92" t-bars and really like them, they match well with the 6 leaf rears, and aren't bad even with the dreaded kyb shocks.

ROT is you want the front/rear ride frequency to be about 10% of each other. with the .92" bars, the rear calculated ~10% stiffer for me, with the 1" bars, the front will end up being the stiffer side and likely have the higher ride frequency, but a lot of it depends on weight distribution. my no power anything slant is lighter on the nose than a BB with PS/PB would be....
Wheel Frequency Calculator

my t-bars were NOS on a member's shelf, if you can only find new, 1" would probably be OK and still match decently with the 6 leaf HD rears.

I also added a helwig front sway bar, that made a massive difference on the feel of the car and how it goes around the corners, no more door handle dragging.

 

[4mulas]

Having done quite a few cars the thing I crave the most and want now is a nice unmolested stock 6 cyl dart like yours and I would Leave it as is. Simple, stylish, and rare! Almost all of them have been hot rodded ip and big blocked this and road coursed that etc….. it would be cool and nice to have a stocker! That’s my vote

 

[abodyjoe]

give @BergmanAutoCraft a call and he will set you up with everything ya need...

the end goal is to have a sporty daily driver.

in what way? do you want it to handle more like a modern car or just handle like a stockish 70 dart? completly different set ups for both...


i'll give you my set up that makes the car feel more like a modern car.. it rides and steers awesome..

you are also going big block so i'm not even considering the slant six in this recommendation...

FRONT
1.08 torsion bars
adjustable strut rods
adjustable upper control arms
hellwig front sway bar
stock lower control arm with Delrin bushings
bergoson steering box (incredible improvement over stock)
billstein shocks
mopar 11.75 disc brakes

REAR
eaton springs (130 pound if i remember correctly)
bilstein shocks
mopar 11x2 drum brakes
may upgrade the spring bushings in the future....

 

[abodyjoe]

Almost all of them have been hot rodded ip and big blocked this and road coursed that etc…

for good reason.. they are boring as hell to drive with a stock 6cyl..

 

[bb70swinger]

Borgeson box is a game changer on power steering car.

 

[pyrogen007]

Having done quite a few cars the thing I crave the most and want now is a nice unmolested stock 6 cyl dart like yours and I would Leave it as is. Simple, stylish, and rare! Almost all of them have been hot rodded ip and big blocked this and road coursed that etc….. it would be cool and nice to have a stocker! That’s my vote

When I got the car back in 2008, I wanted to drag race it so I ripped out the 6cyl and sold it so that is no longer an option.

in what way? do you want it to handle more like a modern car or just handle like a stockish 70 dart? completly different set ups for both...


i'll give you my set up that makes the car feel more like a modern car.. it rides and steers awesome..

you are also going big block so i'm not even considering the slant six in this recommendation...

Correct, I want it to handle/brake more like a modern car.

I have noticed that no one has mentioned mini-tub/spring relocation for wider tires. I assume moving the leaves inward adversely affects road handling?


So far, I'm getting some pretty good info that isn't contradicting in the same manor as some of the other suspension threads, so thanks everyone for the great replies! I really appreciate it.

 

[72bluNblu]

I have read through quite a few suspension threads and find myself more confused/undecided than when I started. I am looking for suggestions on how to proceed in regard to the suspension and chassis setup, the end goal is to have a sporty daily driver. Initially, just to get it running/driving I am installing an 80s truck 318 but I have a 2/3 complete 451 stroker with aluminum heads I might install later. I have some time to save up as I am still putting it back together but priority is getting this car running and driving and upgrading over time, I just need a solid plan on how to meet my goal, below is what I have:

Car info:
70 Dodge Dart Swinger 2 dr Hardtop
225 CI 6cyl - removed and sold
3 spd auto on column - removed, converting to 4 spd
7 1/4 rear axle
4 wheel drums


Suspension/Chassis Parts I have:
Refurbished factory 73+ UCAs, LCAs, strut rods, V8 K frame and disc brake spindles with Energy suspension's Poly Master kit
Stock replacement ball joints
Wilwood Dynalite Pro front disc brakes, 10.75" diameter vented rotors - 4.5" bolt pattern
6 cyl Torsion bars - still in the car
6 cyl Leaf springs - still in the car
8 3/4 housing w/ 489 sure grip center
axle shafts - 4.5" bolt pattern
10 or 11in drums, I believe I have both
Factory power steering gear box
Stock tie rod ends, adjusters, pitman arm and idler arm
Comp Engineering 3 way adjustable drag shocks - probably won't use these.


These are the parts that I believe that I need to purchase to increase the performance of the suspension to meet my goal, what would the priority be in order of greatest benefit first?

Torsion bars
Rear leaf springs
Shocks
Sway bars(front & rear)
Chassis stiffening
UCA upgrade
LCA upgrade
Ajustable/dynamic Strut rods
Delrin bushings
Wheels
Tires

The 6cyl suspension is still in the car because I have been working on the body and rebuilding the HVAC. The rebuilt stuff is not in the car yet so now is the time to weld in the reinforcements to the LCAs and K Frame I assume. I also assume that torsion bars, leaf springs and shocks should be installed at the same time as the front and rear axle assys, please correct me if I'm wrong.

Thanks for the help!!

View attachment 1716276551

View attachment 1716276552

View attachment 1716276554

View attachment 1716276555

I think @abodyjoe pretty well covered it, the one thing I haven't seen mentioned yet is what wheels/tires you're going to put on the car, which is really the place you need to start.

If you're set on keeping 15" wheels on the car then you don't need to go super crazy with the wheel rates, which plays a big part of what torsion bars you'll run up front. You just can't get really grippy DOT legal tires in the 15" wheel diameter for a street car. If you stay with 15's I'd put the torsion bars in the 1.03" to 1.08" range. More than that will be over sprung for the amount of traction you have.

If you're willing to go to 17's or 18's, well, you can get MUCH better tires and therefore can make use of larger torsion bars. I run 275/35/18's on the front of my Duster with 200 tread wear tires, and even with 1.12" torsion bars and Hellwig sway bars there's room to go to larger bars without being over sprung, and that's with a 340 up from (although with iron heads).

Wheel diameter and tire choice also effects the brakes, with 15's on there the 11.75" 73+ mopar disks work really well, same for the 11x2.5" rear drums. I actually ran that set up on my Challenger with 275/40/17's on all 4 corners and the brakes kept up, although I was running a harder tread compound at the time. If you go to 17" or 18" wheels you can run 13" disks up front, with the 275/35/18's on the front of my Duster I went from 11.75's to a DoctorDiff 13" cobra kit and then more recently to the 13" DoctorDiff Viper kit up front, the change to a much softer tread compound allowed additional braking upgrades.

The shocks thing is also VERY important, cheap shocks do NOT keep up with larger torsion bars. KYB's will absolutely ruin your ride quality with bars over 1" in diameter (they suck all the time, but it becomes even more obvious with larger bars). I know, I've done it. I ran KYB's on my Challenger with 1.12" torsion bars for an embarrassingly long time, changing them out for RCD Bilsteins was a night and day kind of improvement.

In the back the leafs are just fine with a decent sway bar, you want to be in the 120-140 lb/in range depending on how the car is set up. 130 lb/in is pretty much the sweet spot. These cars are nose heavy, and they were not nearly as under sprung from the factory in the back as they were in the front compared to a modern car. With my Duster I run 121 lb/in rear springs with my 1.12" torsion bars up front, which are a 300 lb/in rate. I run a slightly larger 7/8" rear sway bar, and on the road the car is well balanced. Calculators are nice and all but when you throw the car into a corner it gets obvious what it wants. Some of that is driver preference too, I personally believe in not being in oversteer already because on a higher HP RWD car it's easy to add some oversteer with the throttle. If you start off in oversteer mode already it takes your throttle option out of the mix a bit.

I have noticed that no one has mentioned mini-tub/spring relocation for wider tires. I assume moving the leaves inward adversely affects road handling?


So far, I'm getting some pretty good info that isn't contradicting in the same manor as some of the other suspension threads, so thanks everyone for the great replies! I really appreciate it.

A 3" relocation does change how the car handles, but it's easy enough to offset with the rear leaf spring rate. For a 3" relocation if you add 10-15 lb/in you're back in the ballpark, or even just a larger rear sway bar. An E-body rear sway bar actually works well with a 3" relocation and is larger in diameter than what you get for an A-body.

But in order for the 3" relocation to be worth it you MUST do a mini-tub. Without the sheet metal work you only get about an extra 1/2" of clearance moving the springs, because that's all the room there is in the stock tubs.

Which brings up another option, DoctorDiff sells a nice 1/2" spring offset. It's just hangers/shackles, so it bolts into the car and doesn't require any cutting on the body. It does still need the spring perches to be moved, but since you're replacing a 7.25" you may be doing that anyway. And even with an A-body 8 3/4 you've got it out of the car and a perch move isn't all that hard.

Which one you need depends on what you want for tires. 100% stock you've only got room for 255's in the back, maybe even only 245's depending on your car's body tolerances. With a 1/2" offset you can squeeze 275's in there, and if you're going to 18" wheels you can run 275's on all 4 corners without too much trimming/rolling.

On a Dart, if you want to go bigger than 275's you'll need the 3" offset and mini-tub. But that will open you up to run all the way to 335's if you want.

 

[pyrogen007]

I think @abodyjoe pretty well covered it, the one thing I haven't seen mentioned yet is what wheels/tires you're going to put on the car, which is really the place you need to start.

I agree, I think I'm set up for success, I'm leaning toward 17 or 18 in wheels. What wheels/backspacing are you using with the 18s, are they custom? I see Enkei on the wheels in your profile pic are those your 18s? I saw a Dart for sale locally a while back with 09+ Charger/Challenger wheels on it so that has me wondering what modern factory take-offs make a good choice? I know the backspacing/offset is not at all what these cars were designed for...

On a Dart, if you want to go bigger than 275's you'll need the 3" offset and mini-tub. But that will open you up to run all the way to 335's if you want.

I had no idea the Darts could fit that wide of tires, wow.

 

[72bluNblu]

I agree, I think I'm set up for success, I'm leaning toward 17 or 18 in wheels. What wheels/backspacing are you using with the 18s, are they custom? I see Enkei on the wheels in your profile pic are those your 18s? I saw a Dart for sale locally a while back with 09+ Charger/Challenger wheels on it so that has me wondering what modern factory take-offs make a good choice? I know the backspacing/offset is not at all what these cars were designed for...

Yeah I have Enkei RPF's on my Duster. In the front they're 18x9, +35 and in the back they're 18x10, +38. They're off the shelf wheels but the fronts were machined a little to open up the hub bore, the RPF's start out at 73.1 mm which is enough to clear the mopar hub but they neck down to a 65mm cap, so I need to have them bored to 73.1 all the way through. The 13" brakes widen the track a little bit, it's about +5mm per side compared to a 73+ mopar disk. But for 275's the +30 to +35 range is where you want to be.

In the back the Dusters have an extra 1" of space in the wheel tubs, and I run a wider 68-70 B body 8 3/4 so the rears wouldn't really work on a Dart, at least not that particular backspace. I have a 1/2" offset and run 295/40/18's, which would take a 3" relocation on a Dart.

I had no idea the Darts could fit that wide of tires, wow.

The 3" relocation really makes a lot of space. 72BBswingers car had a 3" relocation and mini tub, he had 18x12's with 335/30/18's on it and said he still had some space. This is his car (was I guess, he sold it).

 

[pyrogen007]

Both of those cars look amazing, the blue Dart might just be what I am going to work toward, with the modern B5 Blue color like the 2019 Chargers. I really appreciate all the help, thank you to all that replied!

 

[DionR]

I generally look at late model Mustangs for take-off's. The Challenger/Charger wheels are a bit of an unknown since the published bolt pattern is 5x115mm. I have measured wheels that show as 5x114.3mm(5x4.5) but I have also measured new hubs that had the 115mm pattern. I wouldn't run a wheel with the wrong pattern and I can't nail down which it is supposed to be.

I have found '09 GT500's to be a reasonable target for wheels. But I plan to run Scat Pack Brembo's at some point so I have been a little on the careful side.

This is the wheel I bought for the front, haven't decided on the rear wheels yet. Forgestar Mustang F14 Monoblock Piano Black Wheel; 18x9 F15189066P35 (15-23 Mustang EcoBoost w/o Performance Pack, V6) - Free Shipping

When I bought them, they said they worked with an '09 GT500, but now they don't. Not sure what changed.

On a side note, I am of the opinion that Mopar published a rounded value for the bolt circle (rounded up) and that the original parts were 4.5" bolt pattern. I have several data points that lead me to believe this, but they are kind of pointless since the aftermarket parts suppliers appear to be building to the true 115mm bolt circle so I don't trust any of it anymore.

 

[michiganpat]

Having done quite a few cars the thing I crave the most and want now is a nice unmolested stock 6 cyl dart like yours and I would Leave it as is. Simple, stylish, and rare! Almost all of them have been hot rodded ip and big blocked this and road coursed that etc….. it would be cool and nice to have a stocker! That’s my vote

I'm keeping mine a 6, but am so glad I stiffened up the car just a skoash (both in general and in roll rate with the sway bar), as well as upgraded the front brakes to factory disc. stock, my .85" t-bars had a wheel rate of 100 lb/in, the new .92" ones are rated at 150. the rear 5 leaf springs were rated at 85 lb/in, the new 6 leaf 130 lb/in....

 

[michiganpat]

as far as rear end options, I would figure out what offset works best for what you want in the front, and figure out what rear end width you need to support it without spacers. measure your existing rear end width and how much clearance with your existing tires to the inner and outer sides of the wheel and go from there if you are looking to do the same size and offset rims front and rear. I have a spreadsheet I developed in excel to calculate what different rear end widths and offsets work with my duster's measurements....

depending on HP level you decide to go with, Jeep XJ's came with 3.55 geared 8.25's and are 60.5" wide (3.375" wider than my stock 7.25" measured). IIRC liberties are more like 62" wide but come with rear disc brakes on an 8.25. ford explorers are 59.675", rangers 58.5" and come in a wide variety of axle ratios and an 8.8" ring gear axle. SN95 mustangs (thru '04) IIRC are in the same width range as the XJ's and also come with 8.8's....at least around here, 66-70 B body axles are not easy to find anymore....

 

[pyrogen007]

I'll probably stick with 4 matching wheels and go with the 245 or 255 width tires, will def need to measure it all out once I get it assembled.

 

[72bluNblu]

I'll probably stick with 4 matching wheels and go with the 245 or 255 width tires, will def need to measure it all out once I get it assembled.

That's a pretty good plan, there's more tire options especially in 245. That also opens up an 18x8 or 18x8.5 as an option, although you could still run 18x9's and then go to a wider tire later if you wanted without needing to change the wheels again. 255's have a decent selection as well and are a little taller in the sizes you'd be close to running, they still fit on an 18x8.5 but an 18x9 would be better.

Personally I'd still run the 1/2" spring offset, you definitely don't need it for 245's but it would be easier to get 255's in there without having to be absolutely perfect on your backspace.

Sounds like you already have an 8 3/4, not sure if it's for an A-body. With a square set up it would be easier to get a 65-67 B body rear axle. The "problem" with A-bodies is that the track width is not the same front and rear with an A-body 8 3/4 even with BBP axles. So for an 18x8 front wheel you need somewhere in the ballpark of 20 -35 mm of offset, and like 25-35 for an 18x9 (tire dependent of course). But in the back, with an A-body rear, you need more like 12-15mm off offset for those same wheels. That gets a little better with the 1/2" offset and you can do something like run +25's all the way around.

Now you can run 18x8's with a 245 with like a +20 offset front and rear, it will clear up front and in the back you can add a thin spacer if you're running drums or maybe just get away with it if you convert to disks (which widens the track a bit). If you have the 1/2 offset it will just work.

But with the wider 65-67 B rear you can basically run the same offset front and rear, it solves the front/rear track width issue. And that opens up a lot more wheel choices, finding the same wheel in the same width but with different offsets reduces your options, and of course it means you can't rotate wheels either even though you run the same tire size. On my Duster, with the wider 68-70 B rear I'm pretty close to even, running a +35 in the front and a +38 in the back. I have a wheel stagger but I could run 18x10's all the way around with a +30 to +38 offset. With the Dart wheel wells being a bit narrower the 65-67 B works out a little better.

 

[pyrogen007]

Correct, the 8 3/4 I have is suppose to be for an A body.

 

[72bluNblu]

Correct, the 8 3/4 I have is suppose to be for an A body.

So for me, with where you're at with the build I'd honestly try to pick a set of wheels you like, and decide if you want to be able to rotate your wheels.

Some of that is just because I'm a bit of a wheel hound, but the other part is that its a big visual change and once you've put a particular rear axle in the car you're not gonna want to change it. And it will definitely dictate a lot of your wheel options.

The nice thing about already having an A-body 8 3/4 is that you already have the most expensive 8 3/4 housing, so, if you decide you want a 65-67 B body rear axle for its width you shouldn't have any issues selling your A-body housing and for more money than the B housing will cost you.

I would say the biggest thing to do would be pick your tire size and the tires you want. Then you can decide on the brakes, which will cement your track width (especially in the front). From there you can pick the wheels, and see if you can find something you like that will work with the A-body 8 3/4 or if not, what rear axle width will work with the wheels you want.

And that's not to say that you won't be able to find anything for the A-body rear, there are definitely options. But once you've got the rear axle chosen you're pretty much stuck with the offset/backspacing you need to work with it. Heck it even gets more confusing depending on the tire size you want, for 18x7's up to about 18x9.5 it's easy to find +30 ish offset wheels. Once you go past 18x10 suddenly most of the options are in the +12 to +25 ish range. So like for me, if I want to run an 18x11 in the back suddenly an A-body 8 3/4 looks like a better option than the 68-70 B. But under 18x10 the B rear is the way to go.

 

[michiganpat]

But with the wider 65-67 B rear you can basically run the same offset front and rear, it solves the front/rear track width issue. And that opens up a lot more wheel choices, finding the same wheel in the same width but with different offsets reduces your options, and of course it means you can't rotate wheels either even though you run the same tire size. On my Duster, with the wider 68-70 B rear I'm pretty close to even, running a +35 in the front and a +38 in the back. I have a wheel stagger but I could run 18x10's all the way around with a +30 to +38 offset. With the Dart wheel wells being a bit narrower the 65-67 B works out a little better.

if you have a hard time finding a '65-67 axle, it's 59.5" wide, a stock ford explorer 8.8 is 59.625" wide, and can usually be found in yards for a few hundred bucks with 3.55-3.73 gears, limited slips, and disc brakes, and will take anything a big block can give it....



68-70 B body rears are 60.125", which is just a skoash narrower than the SN97 mustangs and XJ 8.25's (60.5")...probably would need to use '05-up +38mm offset mustang wheels if you used that rear end width....

 

[pyrogen007]

What diameter of tires should I be aiming for, factory 205/75-R14s were effectively 26" diameter, closest two I found were 245/45-R18 or 255/40-R18.