Modern Suspension under a 70's musclecar

TL, DR; I want to put Supra suspension under my '73 Duster, front and rear

My project/barn ornament '73 Duster will, come hell or high water, be back on the road soon. I've been kicking around the idea of transplanting the front and rear suspension from a MKIII (86.5-92) Supra underneath it.

(Before anyone jumps on me about this, I'm aware that the stock torsion bar setup can be made to handle, that aftermarket and OEM steering boxes exist to firm up the lifeless feel of the factory power steering, and that you can, in fact, make a leaf-sprung live axle car handle pretty well. I'm still at the hypotethetical stage, and in all likelihood will probably wind up massaging the OEM stuff. Also, the car is a factory slant six/auto car, so no real collector value. Disclaimer over.)

The car will be going (eventually) for a pro touring aesthetic. It will probably eventually see mostly street duty, with some possible autocross/track day use once I get it sorted.

The advantages as I see them of doing this over upgrading the stock setup :

-Big four wheel discs. The stock supra brakes with good pads will stop the 3600 pound 150 mph Supra with authority...they should be more than enough for my 3150 pound street-driven A-body.

-Better steering feel, better ride on the street (compared to how stiffly it will be sprung if I upgrade the stock setup).

-Cheap....better shocks, brake pads and springs and I'm in business with the Supra stuff. I can probably find most of that used. A supra donor car will be cheap (probably free after I scrap what I'm not going to use). Buying the springs, torsion sbars, shocks, steering box and tie rods, etc., etc. for the Duster looks like I could spend a few grand pretty quick. I'd also be able to sell the 8 3/4' that's under it now (factory A-body setup); probably worth a few hundred bucks to the right person.

Obviously the big downside to the Supra setup is the time/difficulty of getting it right. I've never actually messed with a Supra in-depth...I don't suppose I'd get so lucky that it would have everything bolted to a subframe a la Miata, would I?

I think I'd probably have to put a fuel cell in it if I went IRS, that doesn't bother me much but it is an added expense.

I'm sure I'd wind up having to rethink motor mounts as well, but this isn't terribly difficult.

I've done some poking around, and apparently the track width on the two cars is close. The supra is actually apparently a little wider hub-to-hub, but if I use the modern low-offset wheels (think Mustang take-offs) I can probably use the stock width setup, so no custom axles or wheel spacers.

I'd have to build some sort of upper shock mount set up front and rear, since there won't be anything there for the body to bolt to.

Things that are a wash either way:

LSD is easy and cheap for the supra or the 8 3/4, different gear ratios are easy for either as well Bolt pattern is the same, so I'd be using the same mustang take-offs either way, just with spacers if I keep the live axle.

I've also thought about only doing the supra set-up in the rear. That'd get me better handling and ride and big rear discs for a lot less time and energy, since I wouldn't have to mess with steering or motor mounts.

Any thoughts? Huge holes in my logic? Better ideas? I know that a GRM regular (think his name was Sean Korb?) put MKII Supra bits under a 60's mustang several years ago, but I don't think he's active on the boards anymore. Anyone know where he could be found?

The Supra is a subframe and IMHO is a pretty good setup. They do have a lot of metal on them so you can expect a decent amount back from scrap metal. I may know of where some extra suspension setups from a MKIII Supra are. I can ask a friend if you would like.

93EXCivic wrote: The Supra is a subframe and IMHO is a pretty good setup. They do have a lot of metal on them so you can expect a decent amount back from scrap metal. I may know of where some extra suspension setups from a MKIII Supra are. I can ask a friend if you would like.

Good news...subframe in the back as well? I don't suppose the upper shock mounts bolt to the subframes (I wouldn't get that lucky, and it frankly wouln't make too much sense.)

As for looking for parts for me, I appreciate the offer, but I don't think shipping would be feasible. I'm in Missouri, looks like you're in Alabama. I can find a mashed supra parts car around here if I look for a bit.

IIRC yes it is a subframe in the back. And no the shock mounts are not on the subframe. Shipping would probably suck.

PM'ed you Sean's number

1 thought...

When I had a Supra rear/ subframe assembly laying around (for all too long), I noted the it was very heavy. VERY heavy.

That might be nice, depending on how much power you are thinking of putting down.

Oddly enough, a Miata rear suspension is almost the same width as an A-body as well - though I'm not sure how you'd go about making the diff beefy enough.

You'd probably have to reinforce the shock towers to get the front suspension in - I'd sooner try a rack and pinion conversion on the stock A-body front suspension.

SVreX wrote: 1 thought... When I had a Supra rear/ subframe assembly laying around (for all too long), I noted the it was very heavy. VERY heavy. That might be nice, depending on how much power you are thinking of putting down.

Thanks much for the contact info, now that I had the name of the car I found his old website as well.

And yeah, Supra stuff is plenty stout (although an 8 3/4" Mopar is probably not going to break at the power levels I'm putting down).

www.suprang.com

Knurled wrote: www.suprang.com

Can't believe it took so long for someone to mention the Suprang....

You folks are slipping ;)

Oh and to beef up the Miata diff? RX7 diff swap or do what they do for the LS1 Miata's at Flyin Miata.

I would use the Supra stuff over the Miata because that extra weight will be putting extra stress on the brakes and suspension components of a Miata whereas the Supra stuff will be understressed. Also I love this idea btw because I really like both the MKIII Supra and A-bodies.

If you can get $200 for your rear axle, then you'll still be $ ahead swapping in an Explorer or Crown Vic axle with LSD and disc brakes. That was always my plan for my Dad's '65. Other big plus is that the Vic came with numerically low rear gears that you would need with a \6 and no overdrive.

I just bought an Aspen R/T and will be doing the same thing though I hadn't considered robbing a sub-framed suspension system like you're talking. My plan is a little more straight forward, I'm going to cut the factory front stub off and replace it with a Howe road race late model front stub. I'm going to leave the rear leaf spring / live axle for simplicity's sake. It'll be fun to see how you come along with your Duster...

Another approach to an IRS in an A-body:

T-bird Supercoupe rear in a '66 Dart.

turboswede wrote:

Knurled wrote: www.suprang.com

Can't believe it took so long for someone to mention the Suprang.... You folks are slipping ;)

He mentioned Sean in his first post, but couldn't find contact info.

I figured the website would be as good a place to start as any.

Knurled wrote:

I figured the website would be as good a place to start as any.

Yeah, I couldn't remember what he called the car. Kinda obvious, now that I think about it.

T-bird's kind of a neat idea...hadn't really thought about that. Good solution for the back, think the front is still MacStrut, right? The Supra is double A-arms front and rear, which is a lot of why I like it.

Crown Vic is a no go, plenty strong, still a stick axle. Also, car was originally a slant 6/auto, it's not anymore.

psteav wrote: T-bird's kind of a neat idea...hadn't really thought about that. Good solution for the back, think the front is still MacStrut, right?

Nope. The MN12 platform has an SLA front suspension front and rear.

Don't see the point. The One Lap A-body handled well and obviously could cover the street miles. Doubt you'll better that effort and will spend ungodly amounts of time and effort to create a Frankencar that may or may not work, for what benefit? An IRS to rally the thing? Might as well splash a fiberglass replica of the Duster and bond it to the Supra-done.

forzav12 wrote: Don't see the point. The One Lap A-body handled well and obviously could cover the street miles. Doubt you'll better that effort and will spend ungodly amounts of time and effort to create a Frankencar that may or may not work, for what benefit? An IRS to rally the thing? Might as well splash a fiberglass replica of the Duster and bond it to the Supra-done.

The Supra suspension will probably be a lot less money then the One Lap A-bodies suspension.

I would pick the Supra suspension over the T-Bird for one reason, aftermarket support.

forzav12 wrote: The One Lap A-body handled well and obviously could cover the street miles.

Is that the Green Brick '69 Valiant? One of my favorite cars.

Personally, I think I'll stick with the basic-but-tuned torsion bar / leaf suspsension in my A-body Mopar, but I like to see other options explored.

Whatever is done, we want a build thread.

I think the project sounds awesome and I would love to read the build thread. But you said "My project/barn ornament '73 Duster will, come hell or high water, be back on the road soon." That, to me, is incompatible with an undocumented Supra suspension install with diety knows how much custom fab and guesswork. If you want to drive it, do simple swaps not fab work. If you want to work on it for the next year or two, do the Supra suspension.

dculberson wrote: I think the project sounds awesome and I would love to read the build thread. But you said "My project/barn ornament '73 Duster will, come hell or high water, be back on the road soon." That, to me, is incompatible with an undocumented Supra suspension install with diety knows how much custom fab and guesswork. If you want to drive it, do simple swaps not fab work. If you want to work on it for the next year or two, do the Supra suspension.

Nicely put.

I think a properly setup stock suspension on your car will handle track duty just fine for anything other than full on competition. Put some good sized tires on the car, stiffen your suspension, limit body roll, and you'll be surprised how good it'll get around a track.

Xceler8x wrote: I think a properly setup stock suspension on your car will handle track duty just fine for anything other than full on competition. Put some good sized tires on the car, stiffen your suspension, limit body roll, and you'll be surprised how good it'll get around a track.

I think the debate is :Do you want to be on the track next month fine tuning your somewhat stock based suspension, or would you rather be on the track tuning your homebrewed hybrid forum bait in two years?

Granted, we'd all think the suspension swap is cool, but without tuning, it wouldn't matter which path you chose, they would both suck. Give the 'easy' button two years worth of tuning and it will take the supra solution a long time to be better.

A couple things I've noticed with vintage Mustangs, which aren't all that removed from your car.

1. You can spend a LOT of money on many, many high end suspension parts.
2. The structure of the car is limited. You can do whatever you want in the way of suspension, brakes, tires, etc.., but there is a definite limit to what the car itself can take without major mods to the structure.
3. The guys from Cobra Automotive run in vintage racing, and go way faster in a vintage Mustang on a stock-based suspension than I ever could on a high end one.

That said, I'm not saying you shouldn't do it. Just offering a little food for thought.