3 LINK REAR SETUP

Aloha everyone from Cape Town, South Africa

I've got an Aussie Valiant Charger A-body with absolutely no running gear. I'm in the process of fabricating the front Coil over but need some advice/help/insight/wisdom/mana from heaven/enlightenment from you good people if you have it for me.

I want to fab a 3 link! Ta da!
So there are 2 options but I don't know the exact parameters and I'm concerned about Instant Centre as one option seems to be BEHIND! the car.

One is the very good looking but GM Art Morrison kit - pic attached.
The other is the XV kit. Here's an install: XV Level II Suspension Installation by jvike | Plymouth | Barracuda Gen3 | DIY

But just buy one you say! Well here in South Africa the Rand doesn't go as far as the US Dollar and I'd be paying 12 times the price plus 65% import duty so there's that. Oh and massive shipping.

Let's get the conversation started...with the length eye to eye of the lower rods if they are centred under the diff.

Oh yes the diff. Will be using the extremely well priced Torque Sensing Limited Slip Differential based on the Dana 44 but severely beefed up (multiple ratios available). It's a new design and I spoke to the engineer a while back. $599 for a diff that handles 500hp and is Limited slip. Cant get a Try-Trac for that. I can't believe nobody knows about it. It's called a TSD-500.

New Dana 44 Rear End Differential Carrier Assembly Chunk w/ 3.54 Gear Ratio 354 | eBay

Ok so no more rambling. let's start with the lower road lengths eye to eye centred under the diff.

Show me what you got!

Thanks,

Brett

Run it up and down a couple of inches each way and check how much the pinion angle changes.

On a four or three link, generally the lower bars locate the rear (front to back each side) and the upper bar (s) handle the load / weight transfer. I doubt if the sheetmetal floor even with the plate you welded on will handle the load over time and you will be pulling your car apart. I would stick to leaf springs unless you are building a race purpose only car....just my opinion, yours may vary.

Haven't designed or built it yet.
So looking for basic dimensions of the lower arms and info

brewil said:

Haven't designed or built it yet.
So looking for basic dimensions of the lower arms and info

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Having designed one myself, one thing you'll want to look at is the length of the lower links compared to the length of the 3rd/upper link. you want that upper 3rd link length to as close to equal in length as possible. Reason is that the shorter that upper link is compared to the lower links length, the more the pinion angle will change as the suspension travels. Also, 3 link systems almost always result in the loss of the rear seat due to having to be mounted high up on the rear end, usually on the center housing. Now you can offset or angle mount one to help with that and you can try mounting it behind the axle center line to help with that length issue. Just food for thought.

Another thing to think about is will a parallel 4 link work for you? This would let you keep the rear seat and still give you better articulation than a leaf sprung system and better control over your instant center as well as rear roll center. It wouldn't articulate near as much as a 3 link system however.

Lastly, what device are you planning to use to locate the rear? Either a panhard bar or a Watt's link will work. I'm running a Watts set up in my Dart. No track time yet for results/reviews yet.

Also, I agree with Denny, that 3rd link welded to the sheet metal is a terrible idea. Not only that, it's FAR too short and will result in some very radical changes as the suspension travels. That thing cant be more than 6-8 inches long compared to probably 20-24 inch long lowers. Ideally, you want the upper links to be no shorter than 60% on a 3rd link, preferably 75% of the lower length. Example: if your lower links are 20 inches long, you'd want a upper link to be ideally 15 inches or longer with a minimum length of 12 inches. Also, those square tubing lower links are going to cause some issues as well. Go with round tubing and thread it so you can adjust the suspension, you'll want too. 3 links are supposed to be adjustable, those two pics from Fquick.com show a set up that is going to be problematic to say the least.

I'm definitely going with round tubing. I've got Johnny joints left and right thread so adjustment will be easier.
I completely agree with mounting to the sheet metal, not a good idea at all. I've read about offsetting the top link to the axle or side of the pumpkin.
Art Morrison stuff mounts inside the cabin, it has to and I don't mind doing that. I'd prefer to go 3 link for articulation and adjustability over a 4 link and will use the old panhard bar method. Mainly street driven but for the future I'd like to have a good system already installed. Not sure if I'm using a back seat so...
What length lowers have you got in yours?

brewil said:

I'm definitely going with round tubing. I've got Johnny joints left and right thread so adjustment will be easier.
I completely agree with mounting to the sheet metal, not a good idea at all. I've read about offsetting the top link to the axle or side of the pumpkin.
Art Morrison stuff mounts inside the cabin, it has to and I don't mind doing that. I'd prefer to go 3 link for articulation and adjustability over a 4 link and will use the old panhard bar method. Mainly street driven but for the future I'd like to have a good system already installed. Not sure if I'm using a back seat so...
What length lowers have you got in yours?

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Offsetting behind the centerline can be done, but there is a limit there as well. No more than a few inches. Now, what you could do is design the 3rd link to go into the cabin, and instead of a rear bench, run a couple small, short bucket seats and allow the 3rd link to go between them. Make sure you shield that of course for safety should it break. And off setting it to one side of the pumpkin or the other is often done as well.

That kit in that barracuda thread just stinks, i'm not entirely sure if thats a full XV engineering kit or not but I have several reservations about that. And if it is the XVM kit, pretty sure they went out of business a few years ago.

What you want if you were to buy from Art Morrison is this stuff here http://www.artmorrison.com/rearclip-3link.php

You could also look at Ron Sutton's website and see if he sells a clip for it as well. If not, he has a ton of components for very fair prices. ProTouring Rear Suspension - Welcome to the Ron Sutton Race Technology Online Store.

Panhard works great, Id advise an adjustable mount on the frame side though at minimum as well as the bar itself have a length adjustment.

As for adjustment, a 3 link vs a 4 link parallel is going to have as much adjustment as is designed into the kit. The numbers of links really doesnt affect that much as where or how the adjustablility is designed in. Where the 3 link gets the advantage over a 4 link parallel is in the articulation, simply because of the 3rd/upper link being just a single pivot point, front to back, side to side. But its not a giant deal, worth a couple tenths on the stop watch for sure. Both types of kits will eventually bind at some angle within the chassis, the 4 link just does it at a slightly lower angle, so it happens sooner vs a 3 link. Now where the 4 link excels is on the straight away or off the corners, it loads the rear suspension better for straighter, hard launches and they generally can handle the shock of those launches better. So there is a slight advantage on straights, but its slight as well.

As for my lower lengths, I'll have to double check them tonight. I'm drawing a blank off the top of my head.

All this a side, for a mostly street driven machine, setting this up is not really going to be much benefit. 3 links are really for guys looking for tenths of seconds on a road course or even a dirt track. If you're not expecting to see much track time, i agree with Denny, stay leaf springs and quality shocks.

Any idea what max suspension travel up and down is?

brewil said:

Any idea what max suspension travel up and down is?

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not without your measurements. That's subjective on your car and the suspension you're using. So that's something you'll have to measure.

No leaf springs left and to.import them will totally kill.my wallet. It's easier to get steel.cut and bent and welded here at the engineers I use.

So maybe the 4 link is right. No need for the panhard or watts link then.
I've always been cautious about the dreaded idea of "bind".
The art Morrison one is definitely the way to go. But...4 link?

I've also always wondered...does the four link put the IC behind the car and if so how does it affect everything?

brewil said:

No leaf springs left and to.import them will totally kill.my wallet. It's easier to get steel.cut and bent and welded here at the engineers I use.

So maybe the 4 link is right. No need for the panhard or watts link then.
I've always been cautious about the dreaded idea of "bind".
The art Morrison one is definitely the way to go. But...4 link?

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no no, there's two types of 4 links. A trianulated 4 link, which does not use a panhard or watts, but its bind central and not recommend for articulation. The second is one like I'm running, which is a parallel 4 link with either a watts or a panhard bar.

Basically, a triangulated 4 link has the upper links angled inwards towards the center point of the car. A parallel 4 link, the upper links run parallel along the chassis. just as the lower links do. Which is why it requires a panhard or watts to keep the axle centered, left to right.

brewil said:

I've also always wondered...does the four link put the IC behind the car and if so how does it affect everything?

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Instant Center. What are you thinking instant center is?

Instant center is the pivot point of the suspension lines when viewed from the side. Again, that depends on the geometry of your suspension. it depends on the angle of your bars/links in relation to each other. 3 link vs 4 link is going to be nearly the same instant center, assuming the lower links are parallel to the ground and the upper link(s) are set at the same angle.

This video explains it pretty well.



I think you've got a mistaken idea of instant center, your car will have 2, a front and a rear. its simply where the pivot points of the suspension meet.

Below are a few links to help you understand these terms a little bit.

Roll Center Magic

Roll Center Understood

On a leaf sprung car, instant center runs from the contact patch of the tire forward through the line from the front leaf spring mount. or, simply put, the Instant center is the the location of the front spring eye center...

Moving the leaf spring front mounting point down changes the instant center down and forward. The rear spring mounting point doesn't have much effect on the instant center. The length of the spring from the rear end to the front spring mounting point also affects the instant center, longer distance to the front eye from the rear end moves the instant center forward.

If you want a good, off the shelf adjustable 4 parallel kit, I've got a couple I recommend.

4-Link MOPAR Coil-Over Rear Suspension Systems

GTS Rear Suspension | Gerst Tubular Suspensions

The Gerst Setup has a lot more adjustment built into it versus the control freak one but both are very good kits.

If you think you will save money not buying leaf springs I would disagree with you....just price quality coil overs and springs....and you are just getting started.

From what I see, you are building a street ride.....my advise is to talk to someone that has ACTUALLY driven a Mopar street car with a 3 or 4 link. I have tried them all...heim ends, poly ends....even the rubber bushed ends and NONE will give you the plush street ride of your factory or HD leaf springs.

link suspensions (IMO) are for a track race car that requires the ability to change the roll center or instant center ....NEVER needed on the street. The street / road / highway is just too dirty and non predictable to get any advantage.

HemiDenny said:

If you think you will save money not buying leaf springs I would disagree with you....just price quality coil overs and springs....and you are just getting started.

From what I see, you are building a street ride.....my advise is to talk to someone that has ACTUALLY driven a Mopar street car with a 3 or 4 link. I have tried them all...heim ends, poly ends....even the rubber bushed ends and NONE will give you the plush street ride of your factory or HD leaf springs.

link suspensions (IMO) are for a track race car that requires the ability to change the roll center or instant center ....NEVER needed on the street. The street / road / highway is just too dirty and non predictable to get any advantage.

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Coming from a guy who actually engineers and BUILDS suspensions, you should really take his advice....HemiDenny has given you the best advice yet!

HemiDenny said:

If you think you will save money not buying leaf springs I would disagree with you....just price quality coil overs and springs....and you are just getting started.

From what I see, you are building a street ride.....my advise is to talk to someone that has ACTUALLY driven a Mopar street car with a 3 or 4 link. I have tried them all...heim ends, poly ends....even the rubber bushed ends and NONE will give you the plush street ride of your factory or HD leaf springs.

link suspensions (IMO) are for a track race car that requires the ability to change the roll center or instant center ....NEVER needed on the street. The street / road / highway is just too dirty and non predictable to get any advantage.

Click to expand...

I completely agree. Especially the 1st and Last paragraphs

After all..... (as my wife explains to me)...it does not matter how much is spent (in her case, on shoes) , it is about what is saved.

We are only trying to save you money and grief.

Good luck from yours friends in the USA.
Denny

HemiDenny said:

After all..... (as my wife explains to me)...it does not matter how much is spent (in her case, on shoes) , it is about what is saved.

We are only trying to save you money and grief.

Good luck from yours friends in the USA.
Denny

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@berwil let's put it like this, Denny and I agree about 20 percent of the time it seems. This is one of those somewhat rare times.