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Old 06-30-2005, 06:06 AM
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Universal 3-link kit

Hey all,

I need a kit that I can pick up and fabricate into a frame im going to build for my 1970 mustang. It will have a ford 9" rear end. Im looking for the 3-link based on suggestions in other forums, to provide for an overall street course performance vehicle.

so I basically need a kit that i can measure and weld onto my frame and adjust to fit the 9" with proper ride height.

any such thing? Any resources for designing my own if I have to?

Thanks,
Mike Walsh

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Old 06-30-2005, 06:17 AM
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3 link

IMCA 3 bar I think is what you are looking for..2 lower links attached at the outboard ends of the axle housing and what the IMCA guys call a "pull bar" attached at about the center of the axle housing..takes a panhard rod to locate the axle housing..

Might be a bit of a pain to locate that center upper bar in your mustang but then I am told Ford has done that on the new one..may require a bit of modification to the driveshaft tunnel to get it in there...

Have not quite got there yet but that is what I am using on my project..so no pics yet..

Steve Smith autospots has plans for the IMCA chassis which shows the arrangement of the bars and even provides a parts list..that could probably be adapted for your project..

OMT
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Old 06-30-2005, 06:26 AM
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awesome, people keep recomending his literature, I keep forgetting to order it! might just do it this time, 18 bucks for the blueprints seems reasonable

mike
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Old 06-30-2005, 03:46 PM
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As OMT has suggested, take a look at the 2005 Mustang. As a historical matter, this design was also used on the early C-Type Jaguar (the last sports racing Jaguar with a beam axle).

The Jaguar had the upper link offset to the right to cancel driveshaft torque and thus prevent unloading of the right rear on launch. If you could use help in determining the offset and angles to provide exact driveshaft torque cancelation, send me a personal message and I'll be glad to provide it.
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Old 07-04-2005, 08:29 AM
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[QUOTE=BillyShope]As OMT has suggested, take a look at the 2005 Mustang. QUOTE]

I've had this recommendation a few times, my problem has been finding any good resources online that show good detailed design/pictures of the 2005 setup, anybody have any links?

Mike
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Old 07-04-2005, 09:11 AM
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Did find this

Sorry no pics but I did find this write up on the web..

[Quote]For 2005, Mustang’s rear suspension takes a completely different approach to combat wheel hop. Engineers opted for a three-link architecture with a Panhard rod that provides precise control of the rear axle. A central torque control arm is fastened to the upper front end of the differential, while trailing arms are located near each end of the axle.

A lightweight, tubular Panhard rod is parallel to the axle and attached at one end to the body and at the other to the axle. It stabilizes the rear axle side-to-side as the wheels move through jounce and rebound. It also firmly controls the axle during hard cornering.

Constant rate coil springs and outboard shocks are tuned for a firm, yet compliant, ride. The shocks are located on the outside of the rear structural rails, near the wheels, reducing the lever effect of the axle and allowing more precise, slightly softer tuning of the shock valves. [Quote]

The GT version of the car incorporates a separate rear stabilizer bar to reduce body lean further.

This basically is what I am doing on mine using the central located upper "pull rod" to control torque...

OMT
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Old 07-04-2005, 02:45 PM
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Here's a picture of the GT version (with added anti-sway bar):

http://bradbarnett.net/mustangs/timeline/05/05/37.jpg
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Old 07-05-2005, 01:43 PM
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Thanks for all the info guys

So now that I fully understand how the 3-link is setup in the '05 and in general, how am i going to go about finding engineering info so i can make this happen. All along I have been hoping to get a kit, but looking at the 3-link, it seems like it will be pretty easy to build myself.

Some have told me in the past that there are some good books out there to learn from, any of you know specifically any good titles with 3-link design. I suppose there are not many angles to mess up, but i don't really know anything about where all the links should attach to the axle or to the frame, their angle when the suspension is unsprung and sprung etc, how long they should be, and the front/rear angle of the pan-hard etc etc etc

Thanks in advance,
Mike Walsh
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Old 07-05-2005, 03:53 PM
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My 3link setup equations are included in a student workbook which accompanies the book, "Race Car Vehicle Dynamics," by William and Douglas Milliken, when it is used as an engineering college text. You could buy all of this, either through SAE or Amazon, but you'd be spending almost 150 bucks for a lot more information than you really need.

If you're game (and if the administrator will allow it), we could pursue a design in this thread. This design would provide equal rear tire loading during launch (assuming equal initial loading). To start, I'll need the rear tire effective radius (vertical distance from ground to axle centerline), axle ratio, wheelbase, and a rough estimate of the CG height.
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Old 07-06-2005, 06:24 AM
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Quote:
Originally Posted by BillyShope
If you're game (and if the administrator will allow it), we could pursue a design in this thread. This design would provide equal rear tire loading during launch (assuming equal initial loading). To start, I'll need the rear tire effective radius (vertical distance from ground to axle centerline), axle ratio, wheelbase, and a rough estimate of the CG height.
I think this is a great idea, and I think a lot more people would benefit from it than just me. Keep in mind however, that I am more or less in the investigation stage of this build, and I'm not sure if I will be able to get you enough info yet, (or for a while) to be able to figure all this out.

Im working on the body of my car right now, when all that is said and done (I don't work on it in the winter, might be a year+), I will be working on the chassis, so I don't know if there is any way to give you all the details you need..

Is there any way we can work it out in a generic sense with a made up example, this way, myself and everyone else will be armed with the calculation and examples to figure it out for themselves after? Or is this where picking up some good books comes in?
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Old 07-06-2005, 08:11 PM
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Okay, let's get started. The positioning of the lower links is the first order of business. Let's assume some numbers that are easy to work with, though they might not be totally realistic. We'll say, for instance, that the axle ratio is an even 4 to 1. The effective rear tire radius is 14 inches. The offset (from the centerline of the car) of the upper link is 20 inches. The equations assume that the rear locating points of all the links are on a vertical line through the rear axle centerline. The ratio of the vertical distance from the ground to the rear mounting points of the lower links to the distance forward from the rear tire patch to the instant center is equal to the ratio of the effective tire radius to the product of the offset and the axle ratio. This ratio calculates to 0.175, which means that, if the mounting points are, say, 9 inches from the ground, the instant center would be only about 51 inches forward of the rear tire patch. This is a little too close, but, if the mounting points are moved higher, they could interfere with the axle housing. To avoid this, consider the mounting points moved forward and then up. The instant center could be moved to 74.3 inches forward of the rear tire patch if a line through the lower links, when viewed from the side, intersects a vertical line through the rear axle centerline at a distance of 13 inches from the ground. The actual mounting point would obviously have to be forward of the rear axle housing.

The slope of the lower links, when considered positive up from the rear mounting points, is equal to the ratio of CG height to wheelbase minus the ratio of vertical distance to rear mounting points (considered to be on a vertical line through the axle centerline) to distance forward from rear tire patch to instant center. If we assume a CG height of 25 inches and a wheelbase of 100 inches, this calculates to a 0.075 slope (rise over run). As a general rule, the links should be as long as conveniently possible. The longer the link, the less the angle changes for a given suspension deflection.

The rear mounting point of the upper link can be at any convenient height, but, once that height is chosen, the slope is equal to the ratio of the CG height to the wheelbase minus the ratio of the vertical distance to the rear mounting point of the upper link and the distance forward from rear tire patch to instant center. If, in this case, the vertical distance to the rear mounting point of the upper link is 25 inches, an upper link slope of -0.0865 would be required.

This would mean that lines through the upper and lower links, when viewed from the side, would intercept at a point 74.3 inches forward from the rear tire patch and at a height of 18.6 inches. Note that the ratio of 18.6 to 74.3 is equivalent to the ratio of CG height to wheelbase, meaning that the car would neither squat nor rise on launch.

That's about it. A Panhard rod is needed, of course. The Panhard should be horizontal and as long as possible.

The preceding considers ONLY the design considerations for equal tire loading on launch.

It is also recognized that a small error is introduced when the weight of the rear axle assembly is not considered apart from the car's remaining weight, but the resulting error is considered to be within the expected measurement and general setup error.
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Old 07-07-2005, 11:23 AM
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Awesome info here

what is the reason for the 20" offset from the centerline for the upper link? how is this calculated?

"The offset (from the centerline of the car) of the upper link is 20 inches"


im going to try to use the info here, and see what happens when it is plugged into the excel application made by triaged, he posted the link in another topic:

"I am still working on a calculator for 3-link + Panhard suspensions.
This is a BETA version:
http://home.earthlink.net/~triaged/...nkV1.0aBETA.zip
"
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Old 07-07-2005, 01:02 PM
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Quote:
Originally Posted by pigman
Awesome info here

what is the reason for the 20" offset from the centerline for the upper link? how is this calculated?

"The offset (from the centerline of the car) of the upper link is 20 inches"


im going to try to use the info here, and see what happens when it is plugged into the excel application made by triaged, he posted the link in another topic:

"I am still working on a calculator for 3-link + Panhard suspensions.
This is a BETA version:
http://home.earthlink.net/~triaged/...nkV1.0aBETA.zip
"

The reason it is still in BETA is that I haven't had the time to check it against a CAD drawing to be sure I did all my math right. The other main reason is that there are still error messages that come up with parallel links. I need to add in some "IF THEN" statements to get rid of that. I am also still trying to figure out the math to make the travel calculations correct in relation to the Panhard moving things side to side. I'm also still trying to wrap my mind around where the roll point on the Panhard should be...center of the vehicle or center of the bar?

As far as I know the math is right...I just haven't checked it yet.

Also if you want to work with link slopes like Billy Shope is they are on the second page (vector calculations).
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Old 07-07-2005, 01:47 PM
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The 20 inch offset is as arbitrary as the 100 inch wheelbase. Actual offset would be determined by that which is convenient to construct. In general, you'll have less trouble "fitting things in" if you maximize the offset.

While I'm not trying to discourage you from using Dan's software, I would point out that the math is so simple that use of an Excel program really isn't required. Wait a minute! I see what you're saying. You're going to put the figures for my imaginary car into Dan's software. Yes, that would be a good check.

Last edited by BillyShope; 07-07-2005 at 01:53 PM.
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Old 07-07-2005, 02:40 PM
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Real life

well I am at about the point where I need to get "figgered out" on the one I am working on..106" wheelbase with a Ford twin I beam front..

As far as the Panhard bar is concerned I do not think it moves the axle side to side all that much so that piece could be taken to be what it is..the axle only moves about 6" total and that is not enough of a rotation of the panhard to affect anything..at least in my estimation..

the height of the panhard does affect height of roll center tho I will need to look that up..

I can get some actual measurements of the locations and lengths of the lower locating arms and the upper..Note: there are some real life packaging requirements that need to be met..

All the calcs have kinda boggled my mind as I have not done that in a while soooooo..will need to puzzle that one out..

If any of you would like I can put up my dimesions to work with..

OMT
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