3 link for my 65 falcon

[Bryce]

Since i officially started building the parts i decided to start a thread. This way i can keep track of my progress.

I ordered my currie 9".

and welded on the upper brackets for the top link. Pic attached.

next will be to make the Watts link and coilover bracket that attaches to the car.

Oh.... and i plan on not taking the car of the road for more than a weekend at a time as i build this. So it will be running leaf springs with clamp on pads with the new 9" housing. and just for fun i will be lowering the car 2" in the back with the leafs and i am going to build a set of traction bars.

so i will run the leafs with a watts link at some point.

then build the upper link to car bracket.

I have not decided if im going to run a sway bar yet. any input. I think i can easily make future changes to accomodate this.

[Norm Peterson]

When you get around to building the chassis-side bracket for the upper, don't under-estimate the load in the upper link (think wheel hop under acceleration and fatigue effects). I'd guess plan on adding some longitudinal structure to pick up the bracket loads.


Norm

[Bryce]

thank you Norm.

My plan was to grab floor and the frame rails (if you can call them that, HAHA)

Norm, one question for you. what is the length of the new mustang upper link.

Mine will be short around 12" but that keeps it out of the rear seat. i still think its longer than the new mustang. and look how well they can perform.

[Norm Peterson]

The upper link in the S197 Mustang is about 8.5" long, measured pin to pin.


See also post # 14 here (https://www.pro-touring.com/forum/showthread.php?t=47364) (the link lengths are from on-car measurements I made that should be within 1/16" or so.


Norm

[Bryce]

thanks norm.

as always you have great information.

[LowBuckX]

8.5 Thats way short. Why would they have done that? Id at least double that.

[Bryce]

yep thats a short link. with minimal suspension travel and a short wheelbase car it can work without a crazy amount of pinion angle change.

[Norm Peterson]

8.5 Thats way short. Why would they have done that? Id at least double that.
Actually, it's a bit better than GM's A/G body 4-links, which are only about 7.75" long in side view projection.

I suspect three related reasons - packaging space under the floorpan, rear seat room and minimizing the likelihood that the upper link (or part of it) would become a spear in a rear-end collision. For a race car or serious autocross car neither of the interior considerations would matter and you'd likely modify the floorpan so you could fit what you wanted.

From the rest of the measurements I took, the rate of pinion angle change looks to be around 1°/inch of bump travel. I'll assume that that's kind of high (it certainly would be if you were looking at camber gain in a car built to corner). But at least the anti-squat is fairly stable over the first two inches of bump travel even though the IC moves rearward quite a bit.


Norm

[Mean 69]

"lore" has it that the orginal plan for the Mustang was to have IRS, but the bean counters ruled against it. Becuase a large part of the factory package was already defined, the suspension had to be designed around packaging considerations, and in a very short amount of time. I believe this to be true as I have heard it from multiple sources close to the action at Ford. Don't blame the suspension team at Ford, blame the accountants. Funny, the earlier Cobra Mustangs had IRS (best if done well), and a Mac-strut front (generally not the desired approach). Now, it's a stick axle 3-Link (good if done well), and an SLA front (best if done well). The new Camaros went the other way around.....

Interesting data on the migrations, Norm. I would have guessed that it would be larger (pinion angle change in particular), dependent upon the lower link length as well obviously.

But yes, if you were to clean sheet a design, I'd say that error on the long side is a lot better for kinematics/suspension performance. Just make sure you sharpen your pencil on the load requirements and material/strength side of things.

Fun stuff, you will come out significantly more educated after going through the project, best of luck.

Mark

[Bryce]

yes at one point the mustang had a IRS designed for it. but the lack of performance improvement and the high cost stopped production of this setup. the reason for lack of performance was due to the lack of a good tire.

[Bryce]

update:

fully welded upper housing link and painted in black hammertone, one of the toughest rattle can paints i have used.

[Norm Peterson]

Interesting data on the migrations, Norm. I would have guessed that it would be larger (pinion angle change in particular), dependent upon the lower link length as well obviously.
It's progressive, being more like 2°/in once you pass 2" bump.


Norm

[Bryce]

so i got some better measurments and dimension. the lower links will be 23" long. they will be adjustable from flat to 5* inclination and the upper mount will be 14" and 8* decline and adjustable all the way to flat. this will give me adjsutment from 0 antisquat to 150%. but only a 40" IC. is that too short?

[Norm Peterson]

150% is likely more than you'll ever need. What is the SVSA length (IC) at 100% A/S?


Norm

[Bryce]

58" at 100%
and 136" at 54%

[JRouche]

update:

fully welded upper housing link and painted in black hammertone, one of the toughest rattle can paints i have used.

Hey!! Looking good. You have some solid welds and that bracket is stout. I LIKE!! Good to see you posted a fire watch for post welding too. He (or she) looks more alert then some of the guys I have worked with. Keep the pics rolling. I am a fanatic for looking at the build pics. JR

[Bryce]

I wish i could take credit for the welds but i outsourced them but my guy did it for $20. Yep, my shop dog, mollie, is always in the garage with me.

i will keep pics coming for sure.

[novaderrik]

that is one big dog to be able to carry that rear end housing around in it's mouth like that. Clifford would be a better name..

[Bryce]

haha, thanks.

she is only 60lbs. but still thinks she is a lap dog.

I was on vacation in Mammoth last weekend doing some hiking. so updates will happen this week

I was thinking about buying a fays2 watts link to save time. but still contemplating. It would only be pieces as i already have the watts axle mounts and i would get aluminum rodends and bars.

[JRouche]

I was thinking about buying a fays2 watts link to save time. but still contemplating. It would only be pieces as i already have the watts axle mounts and i would get aluminum rodends and bars.

Thats pretty close to what I did. Jim is cool about selling the parts you need. Aluminum rod ends? Or just the bars? Cant wait to see the pics. JR

[baggins]

is the hammertone you used made by rustoleum? also is it just the regular black tone?

[Bryce]

Thats pretty close to what I did. Jim is cool about selling the parts you need. Aluminum rod ends? Or just the bars? Cant wait to see the pics. JR


yes aluminum rod ends. they still have a steel ball. they can take the same loads but half the weight.

Jim is really cool. I have been emailing him this week.

[Bryce]

is the hammertone you used made by rustoleum? also is it just the regular black tone?


yes it is. regular black ends up a little gray.

[Bryce]

update.

so the 9" housing with the 4.11 gears is in. im running it with the stock leafs and lowered it 2.5". I modified the housing so i can use clamp on leaf pads and change them out later for my lower link/ coilover brackets.

i am currently working ona desing for the upper coilover mount and watts link, then the sway bar and finally the upper third link mount on the chassis side. as i build this i hope to continue to drive the car.

so to make it a better driver i modified some clamp on traction bars from summit. it works really well. over 100% antisquat. good for the strip and not much else. but it will be fun.

the 4.11s were a huge difference stepping up from the 2.80s. WOW.

[BillyShope]

Have you given any consideration to the cancellation of driveshaft torque effects with the 3link? (This might be a bit late, as I noticed the first thing you did was weld on the upper link attachment point to the rear axle.) As I'm certain you're aware, the driveshaft torque tends to unload the right rear during forward acceleration. Jaguar overcame this inherent asymmetry...with a RWD beam axle car...by building a cancelling asymmetry into the 3link used in the Le Mans-winning C-Type competition car.

I have a spreadsheet for determining the proper geometry at my site (Page 18).
http://www.racetec.cc/shope

[Bryce]

yes i have thought of that. One of the cars in my garage, a intermeccanica omega, has that type of rear suspension. It was a holman moody designed car with an intalian body and ford running gear. I kinda like the idea.

I have already commited to the centered upper link. and i have looked at all your calculations. very helpful.

my idea is to run a huge sway bar for drag racing and this will cancel the engine torque. while also preloading the passenger side.

[BillyShope]

my idea is to run a huge sway bar for drag racing and this will cancel the engine torque. while also preloading the passenger side.
While this will help equalize rear tire loading during forward acceleration, it can never do the job alone. This is because there will always be considerable roll stiffness at the front of the car. Either static preloading or unequal spring rates across the front will be necessary. You're going to a lot of extra trouble, all of which would have been avoided with the asymmetric 3link.
http://www.racetec.cc/shope

[Bryce]

i could always add it on later and run both brackets and change bars and see if there is a difference.

[Bad Bird]

Is it possible to cancel the driveshaft torque in another fashion, such as using a panhard bar?

[Bryce]

Is it possible to cancel the driveshaft torque in another fashion, such as using a panhard bar?


panhard is only for side load under suspension compression. not for driveline torque. I think only a swaybar or offset upper link will cancel it.

[BillyShope]

I think only a swaybar or offset upper link will cancel it.
The high rate swaybar will never totally cancel. In addition, it should be disconnected before the car is driven on the street.

There is, however, another way...besides an asymmetric rear suspension...to dynamically cancel driveshaft torque. Different rate springs can be used across the front. In other words, if the spring rate at the right front is greater than that at the left front, the effect...during forward acceleration...is the same as with an asymmetric rear suspension. Adjustable coilovers will be required, of course, to statically equalize the rear loading. Again, there is a setup spreadsheet at my site.
http://www.racetec.cc/shope

[MoparCar]

Does anyone have a "good" picture of the factory five offset 3-link they offer on their kits? It has tight packaging, but I've never found a really good picture or details. Their offset link connects rear of the axle tube instead of at the top or front.

[parsonsj]

Different rate springs can be used across the front. In other words, if the spring rate at the right front is greater than that at the left front, the effect...during forward acceleration...is the same as with an asymmetric rear suspension. Adjustable coilovers will be required, of course, to statically equalize the rear loading.Of course, that's drag racing only, right? You wouldn't want asymmetric springs in a street, autoX, or road racing car.

jp

[BillyShope]

Of course, that's drag racing only, right? You wouldn't want asymmetric springs in a street, autoX, or road racing car.
jp
That's a very good question. I considered this when, at my site, I suggested that rates be chosen so that the front roll stiffness remained essentially unchanged. Oval track racers commonly run very different spring rates across the front and are still able to make the occasional right turn when required. I had a constructor friend (now deceased) who had the opportunity to do some testing on a sports car circuit with a car that was set up for El Cajon, a 3/8 mile asphalt track. He said he was very impressed and surprised with the handling of the car in both left AND right hand curves.

Certainly, the roll axis is going to be moved laterally, but whether that would make the car totally unmanageable is a question I cannot answer. Frankly, I doubt it, but that's just an opinion.
http://www.racetec.cc/shope

[MoparCar]

I found these picture of the factory five offset 3-link. What's the thoughts on the rearward (back of axle centerline mount)? Any disadvantages? Advantage I guess would be less upper arm into the passenger compartment. It would cause some gas tank issues. The small arm to the diff from the 3rd link mount is a stiffening brace only.

Anyway just some additional ideas. Is there an ideal amount of offset to the side for an offset 3rd link?

Wes

[Norm Peterson]

It results in minor changes to anti-squat. Not the amount at static ride height, which you could "force" to be at the same value as a same-length upper that mounted directly above the axle center. I'm thinking about the rate at which the anti-squat varies as ride height changes. I don't know offhand whether it would be a tiny benefit or a similarly small disadvantage, but I doubt that it would be enough to matter.


Norm

[BillyShope]

I found these picture of the factory five offset 3-link. What's the thoughts on the rearward (back of axle centerline mount)? Any disadvantages? Advantage I guess would be less upper arm into the passenger compartment. It would cause some gas tank issues. The small arm to the diff from the 3rd link mount is a stiffening brace only.

Anyway just some additional ideas. Is there an ideal amount of offset to the side for an offset 3rd link?

Wes
The rearward mounting allows use of a longer link, the obvious advantage of which is to minimize antisquat change with a given deviation from ride height.

I would define "an ideal amount of offset" as that which would provide complete cancellation of the driveshaft torque effect, meaning the rear tires would be equally loaded during forward acceleration. Since the link loads are proportional to the percent antisquat, the antisquat determines the suspension geometry. For a dragrace car, the antisquat should be at 100%, since this minimizes load oscillations at the rear tires and thus maximizes forward thrust. But, for an autocross car, this value of antisquat would almost certainly cause wheel hop problems during braking.

On Page 18 of my site, there is a spreadsheet which yields the geometry for total cancellation and allows the user to input the desired percent antisquat and such things as the rear mounting points of the links, including their horizontal relationship to the rear axle centerline.
http://www.racetec.cc/shope

[MoparCar]

Billy,
What am I doing wrong with your speadsheet? When I hit computer it always comes up with "NaN" in the answer spaces.

Thanks for all of your information. Very valuable.
Wes

[BillyShope]

Billy,
What am I doing wrong with your speadsheet? When I hit computer it always comes up with "NaN" in the answer spaces.

Thanks for all of your information. Very valuable.
Wes
I'm assuming you're using the spreadsheet on Page 18.

My first guess is that you entered too low a value for the desired percent antisquat. If there are insufficient vertical force components in the links, it is impossible to cancel the driveshaft torque. Even an autocross car should be able to tolerate 80% or so with no braking problems. The default values act as you describe when the antisquat percentage is changed to less than 51%.

If the above is not the case, does it do this with the default values? If so, it's a browser problem and I can't help you.

If the default values work, change one value at a time until you have a problem.

If all else fails, give me a call or post the numbers you used here.

I strongly believe, however, that my first guess captured the problem.
http://www.racetec.cc/shope

[LowBuckX]

I found these picture of the factory five offset 3-link. What's the thoughts on the rearward (back of axle centerline mount)? Any disadvantages? Advantage I guess would be less upper arm into the passenger compartment. It would cause some gas tank issues. The small arm to the diff from the 3rd link mount is a stiffening brace only.

Anyway just some additional ideas. Is there an ideal amount of offset to the side for an offset 3rd link?

Wes

Thats how mine is planned. But I didnt think to use axle clamps. Thats a score for me because welding the axle tube in not what I want to do incar.

https://static1.pt-content.com/images/noimg.gif

[BillyShope]

Billy,
What am I doing wrong with your speadsheet? When I hit computer it always comes up with "NaN" in the answer spaces.

Thanks for all of your information. Very valuable.
Wes
Also, Wes, if you can't work with the percent antisquat that you want, you might consider putting the odd link BELOW the symmetrical link pair. Just to see how this works, try switching the "10" and "18" in the default vertical heights and you'll see that you can take it all the way to zero percent antisquat and still get driveshaft torque cancellation.

WARNING: That single lower link would then be carrying a VERY large load.
http://www.racetec.cc/shope

[MoparCar]

Also, Wes, if you can't work with the percent antisquat that you want, you might consider putting the odd link BELOW the symmetrical link pair. Just to see how this works, try switching the "10" and "18" in the default vertical heights and you'll see that you can take it all the way to zero percent antisquat and still get driveshaft torque cancellation.

WARNING: That single lower link would then be carrying a VERY large load.
http://www.racetec.cc/shope

Billy,
The sheet works as long as I don't go much lower than 10" off the ground for the lower links. If I put 9" in the value, then the sheet does not compute.

Thanks, Wes

[BillyShope]

Billy,
The sheet works as long as I don't go much lower than 10" off the ground for the lower links. If I put 9" in the value, then the sheet does not compute.

Thanks, Wes
Again, this is a matter of not having enough vertical force in the links to achieve a moment balance. If you "sneak up" on that minimum height, you'll see that the instant center is headed for infinity. The computer is trying to find a combination that will work.

If you really want that 9 inch pivot height, you'll have to lower the upper (odd) link and/or increase the odd link offset.
http://www.racetec.cc/shope

[Bryce]

i like where this thread is going. a lot of good ideas.

i like the idea of the offset upper link.

[MoparCar]

One of the things I've been sketching out and running the numbers on is an offset odd link with the actual link being vertically "stepped" sort of like this ___/---- (sorry no keys that would make it look correct) more or less a step up at the rearend. Still connecting the calculated suspension points but with a step in the link. The reasoning would be if you offset the link from the center out of the driveshaft tunnel you might be able to manipulate the mounting points and calculations to still reach the suspension design goals, but possibly not have to cut into the back seat or not as much--that being the reason for the stepped link. This may be more realistic using the rearend mount like the factory five where it extends back from the axle tube a bit. I am certainly not a suspension designer, only looking at possible packaging solutions. Tell me if I'm really being stupid with this thought!

Wes

[BillyShope]

Tell me if I'm really being stupid with this thought!
Wes
No, not at all. You can form it into a pretzel shape if you like. Just remember that, when it comes to analysis, you must treat it as a straight link between the 2 pivot points.

Falcon65, I just remembered that I once owned a '65 Sprint. Stock except for a five liter engine and rear swaybar. Some guy saw it and wanted it for his collection somewhere in the Southeast. (I was in California at the time.) He made me an offer I couldn't refuse.
http://www.racetec.cc/shope

[Bryce]

No, not at all. You can form it into a pretzel shape if you like. Just remember that, when it comes to analysis, you must treat it as a straight link between the 2 pivot points.

Falcon65, I just remembered that I once owned a '65 Sprint. Stock except for a five liter engine and rear swaybar. Some guy saw it and wanted it for his collection somewhere in the Southeast. (I was in California at the time.) He made me an offer I couldn't refuse.
http://www.racetec.cc/shope

I would not recommend putting a bend in any link. the upper link is in compression and tension. During tension it will try to staighten out the link. with the bend it incorporates a weak point. not a good idea, you dont want any deformation or flex. it would need to be made very strong to take a bend in the link. maybe a solid rod would work.

Billy, Falcons are a really cool car. i have not recieved an offer on mine. hopefully i will not get one i cant refuse.

[BillyShope]

I would not recommend putting a bend in any link.
I agree, of course, though it has been done. Jaguar used an "S" shaped Panhard in the C-Type.

I was just trying to make it clear that, no matter how it's shaped, it functions as if it were a straight rod between the pivot points.
http://www.racetec.cc/shope

[MoparCar]

I agree on the strength aspect. Highly loaded part. Possibly a CNCd alloy part definitely not just a bend in a piece of DOM tubing!

Thanks, Wes

[Norm Peterson]

Long-term, I think I'd feel a lot more comfortable about appropriately-selected bent (hydroformed?) tubing than anything billet in this application. A proper forging with the end details for attaching the bushing or rod ends CNC'd would be a different story. No numbers, and I'm not a metallurgist, so let's just call it a vague uneasiness about grain structure, load paths, and stress intensifications.


Norm

[LowBuckX]

This reminded me of a pic I once saw on this site cant beleive I found it..

******SNATCHED FROM POST****I think this is the upper link you guys are talking about. I fabricated it, and Louie was the designer. It is made with 3/6" 4130 for the sides and 1/8" 4130 for the top and bottom. The receivers are 4140 Light Racing pinch units that have the highest strength rating in the industry (if you dont believe me then check out lightracing.com). Then we used our Chromoly Heims with the liner to top it off. ********


https://static1.pt-content.com/images/noimg.gif

[MoparCar]

Yes, I thought I saw that before. Was it used in an application or any more details?

Wes

[Norm Peterson]

That approach works. Mostly, anyway (I'm not too crazy about the sharpness of that not-quite-90° inside corner at upper left and would much rather see a radius there).


Norm

[John Wright]

That approach works. Mostly, anyway (I'm not too crazy about the sharpness of that not-quite-90° inside corner at upper left and would much rather see a radius there).


Norm
You can weld up that corner and shape the weld to get a more radius'd profile there. That would help with the stress raiser that you pointed out.

[LowBuckX]

Im off to work but if you search CAD 3 link its the second from last post but it has little info but you can PM the poster I think it was MATT@GMACHINE

[Bryce]

was that the link GMR was building for their mustang?

i think it would be strong enough but the high stress points concern me. now the link has a internal bending moment not just a tension compression force.

Im sure it would still work. i would want to check for stress fractures periodically.

in my situation i dont see how that bend would help with packaging issues. so i will stick with 1.25" DOM with 3/4 chromoly rodends. 1.25" gives me a factor of safety of 5 and the rodends would fail first.

[Bryce]

just had a thought. Maybe i will make my 3 link and then modify it to be a tourque arm suspension. Then modify that and make it a decoupled torque arm. This is just a thought to determine what setup works the best. and then i would take it to the strip and lay down some 60ft times.

this is just a passing thought.

[BillyShope]

just had a thought. Maybe i will make my 3 link and then modify it to be a tourque arm suspension. Then modify that and make it a decoupled torque arm. This is just a thought to determine what setup works the best. and then i would take it to the strip and lay down some 60ft times.

this is just a passing thought.
I think the KISS principle is best applied here. Since this is a dragstrip car, simply pick one design, adjust for 100% antisquat and equal rear tire loading, and build it and forget it.
http://www.racetec.cc/shope

[Bryce]

it will be a best of all worlds car. I want to be able to tune it for all conditions.

[BillyShope]

I want to be able to tune it for all conditions.
For what will you "tune" it? Once you have 100% antisquat and equal rear tire loading for any and all values of driveshaft torque, there's nothing else to do. Oh, I suppose it could be argued that a strip might have "too much" bite. In this case, you add air to the tires; you DON'T do any suspension tuning.
http://www.racetec.cc/shope

[LowBuckX]

I think he is talking about Any racing he does will be on the strip then he wants it to corner well on the street.
My 3 link can be adjusted from 39% A/s to 140% A/S with a few hole changes.

[Bryce]

I think he is talking about Any racing he does will be on the strip then he wants it to corner well on the street.
My 3 link can be adjusted from 39% A/s to 140% A/S with a few hole changes.


correct, im aproximatly 45% to 145% with hole adjustments. ride height and pinion angle will be adjustable for different tire diameters. and preload from side to side will be adjustable also different sway bars will be easily changed from a steet/auto-x bar to a much stiffer drag bar. also adjustable length arms will be used with both setups to fine tune any sway. Im trying to build this as universal as i can. so that it ends up being a multi purpose suspension. I know you cant have the best for all conditions but im looking for good in all conditions.

[LowBuckX]

correct, im aproximatly 45% to 145% with hole adjustments. ride height and pinion angle will be adjustable for different tire diameters. and preload from side to side will be adjustable also different sway bars will be easily changed from a steet/auto-x bar to a much stiffer drag bar. also adjustable length arms will be used with both setups to fine tune any sway. Im trying to build this as universal as i can. so that it ends up being a multi purpose suspension. I know you cant have the best for all conditions but im looking for good in all conditions.

We think alike.

[BillyShope]

I think he is talking about Any racing he does will be on the strip then he wants it to corner well on the street.
My 3 link can be adjusted from 39% A/s to 140% A/S with a few hole changes.
Yup! I forgot I was posting in a forum which includes autocross. Certainly, you'll want to back off from the 100% antisquat when you're concerned about wheel hop during braking.
http://www.racetec.cc/shope

[Norm Peterson]

Then plan on keeping really good notes and try not to get lost in the tuning. Some adjustability is probably a good thing here, but won't necessarily be so good in the overall scheme of things if everything is adjustable in increments that are too fine and cover too wide of a range.


Norm

[BillyShope]

Also, if it is to be a "jack of all trades," I hope you arranged for 100% driveshaft torque cancellation at 100% antisquat for optimum dragstrip performance.
http://www.racetec.cc/shope

[Bryce]

yes sir,

im still trying to figure out the packaging of the rear sway bar. I will have a drag bar and a street/auto-x bar.

I want to do a chassis mount bar with links on the rear end but it seams like that is harder to package for my car.

to simplify i may go with a panhard and change later to a watts if needed. this would give me a little more room for everything.

[Bjkadron]

Um... Why not do a splined swaybar and just have different adjustment holes for drag and street/auto-x? If you have a fairly stiff bar you could have long arms for the "softer" street rate and short arms for the drag. Or just different holes in the same bar. This would be a chassis mount bar that I am referring to.

[Bryce]

that would work but i think the sway bar would not have enough adjustment. I want to run a really stiff bar for drag and a softer bar for the street. something around a 1.5" hollow for drag and a .625" solid for the handling. what i would like to do is make the arms the same and run a different bar. and of course the arms would be adjustable.

[BillyShope]

yes sir,

im still trying to figure out the packaging of the rear sway bar. I will have a drag bar and a street/auto-x bar.

Wouldn't it be far simpler to supply bracket adjustment holes at the rear (and/or front) of the lower links? Simply increasing rear roll stiffness will, indeed, help to cancel driveshaft torque unloading of the right rear while dragracing, but, since there will always be some roll stiffness at the front, this technique can never be completely successful. If, however, you allow adjustment to a higher right side antisquat than left side, you allow the possibility of complete cancellation and equal rear tire loading for any value of driveshaft torque. And, of course, you'd never have to touch the rear swaybar.


to simplify i may go with a panhard and change later to a watts if needed. this would give me a little more room for everything.
You'll never "need" a Watts. Stick with the Panhard.
http://www.racetec.cc/shope

[JRouche]

that would work but i think the sway bar would not have enough adjustment. I want to run a really stiff bar for drag and a softer bar for the street. something around a 1.5" hollow for drag and a .625" solid for the handling. what i would like to do is make the arms the same and run a different bar. and of course the arms would be adjustable.

I think thats a great idea. If you go with a splined bar you can swap just the bar out and keep everything else. And the bars are only 90 bucks.

For example, speedway engineering bars come in a large assortment of sizes. Like their 1.25" OD bars. Im not sure what rates you are considering. But for an example. A 39" long bar with 10" arms can have rates everywhere from 260-538 lbs. And thats just one bar length. Without adjusting the arm length (mounting holes). They have many sizes available.

I have one of their bars for each end of my car. The rear bar is a pretty straight forward install. The front bar was a lil trickier. I had to bend the arms to clear the wheels.

And while trying to figure out all the combos of rates I took their numbers that are for two inch arm length increments and figured out the rates for each inch of length, and its pretty linear across the length. That way I could drill the arms for the exact rate I wanted, not just in the inch lengths they show. You can get to the rate you need with where you drill your holes in the arms. JR
http://www.1speedway.com/swaybar39.htm

[JRouche]

You'll never "need" a Watts. Stick with the Panhard.

Yes, and no.. If he can fit a long enough PH bar in there then yes, they do work just fine. Ideally the bar would go from wheel hub to wheel hub in length. But thats tough. So they get a lil shorter and shorter. Before you know it they are 24" long (mine) and they dont work.

I have a lil sports car that has a pan hard bar, and it is almost hub to hub in length. It works great!!! No wallowing about of the rear end at all. But with that 24" bar just taking a slow turn onto a street the dip in the road caused the rear of the car to feel like I lost the rear end. LOL Yeah!! Like it completely came loose, and that was at 3mph, ugly for sure.

Packaging for both systems can be a headache. But sometimes one will package better than the other. For me it was the watts link that won out. And I really looked hard to use a decent length PH bar. I think I was just going for a short bar, and even after all kinds of goofy mounting ideas I still couldnt get it in there. I looked at above, and rear bar mounting ideas, no good. The closest I came was a rear mounting bar. But the entire length of it wouldnt clear my tank. And so I was able to fit the watts in the same space, but it had less moving parts.. LOL Now yer saying LESS moving parts?? What!!! Yer loopy.. Ok, maybe not less moving parts, but less moving area of parts. Instead of having one long 40" bar sweeping the entire area I have 28" of material swinging with the car body. Frame mounted center pivot. Only the links move. Not alot of interference.

So thats where I see the advantage of a watts link is, with the packaging. If you compare it with a similar amount of lateral controlling pan hard bar which is gonna be long to control the rear end.

Plus they just look damm cool. Cept when someone sees it and asks, whats that??? Then its school time :) JR

https://static1.pt-content.com/images/pt/2009/05/e-3.jpg

[BillyShope]

I think thats a great idea. If you go with a splined bar you can swap just the bar out and keep everything else. And the bars are only 90 bucks.
Keep in mind that his goal is a "universal" setup with a minimum of compromise. When it is possible to achieve equal rear tire loading by simply switching the locations of a couple of bolts, the use of two swaybars would constitute both an unnecessary compromise and an unnecessary amount of work.


I have a lil sports car that has a pan hard bar, and it is almost hub to hub in length. It works great!!! No wallowing about of the rear end at all. But with that 24" bar just taking a slow turn onto a street the dip in the road caused the rear of the car to feel like I lost the rear end. LOL Yeah!! Like it completely came loose, and that was at 3mph, ugly for sure.
Without knowing the roll rate of the car and the size of the dip, I can't accurately calculate the lateral shift of the axle housing, but it would seem that a 2 inch drop of one end of the 24 inch Panhard captures the worst of conditions. This would result in a lateral shift of 0.083 inch if the Panhard was originally horizontal. Your seat of the pants is much, MUCH more sensitive than mine. And, since the upper and lower links of the Watts linkage operate through different angles, even a Watts would not have kept the axle perfectly located.

Since I consider its design perhaps the ultimate for a RWD beam axle car, I keep referring back to the early Jaguar C-Type, which managed to win Le Mans with a short Panhard.

He will never need a Watts with a '65 Falcon.
http://www.racetec.cc/shope

[Bryce]

every part of the rear setup will be adjustable. i can change the mounting location front and back of all links as well as length. i dont have an issue changing sway bars, that would be about a 25 minute operation.

as far as a watts vs panhard. watts on paper is perfect. however, when it comes to actual use with a limited travel rear suspension how much performance is gained with a watts? i think a panhard will be sufficient and cheaper and easier fab. However i will build this modular so a change can be easily made if i want to run a watts in the future.

[BillyShope]

i dont have an issue changing sway bars....
But, I would imagine you'd just as soon save the time and expense, wouldn't you? All I was pointing out was that, with the adjustment you say you'll have, you'll have not just an alternative, but a BETTER alternative. See my site for the adjustments required.


watts on paper is perfect.
This is true ONLY if...at some point in the suspension travel...the side links are both horizontal. Unfortunately, this configuration is rarely seen (though the above picture appears to be such a case).


when it comes to actual use with a limited travel rear suspension how much performance is gained with a watts?
This is easy enough to calculate. To determine the maximum lateral shift of the axle housing, first estimate the maximum vertical travel, of one rear wheel relative to the other, expected in competition driving. (This is NOT the maximum as determined by maximum suspension travel, but the maximum you would expect to encounter while attempting to control the car.) Divide this number by the rear track. Determine the arc sine. Determine the cosine. Subtract from one. Finally, multiply by the Panhard length and you have the lateral shift of the axle housing.

I think you'll be surprised at how small a number. And, remember, this is the MAXIMUM.
http://www.racetec.cc/shope

[Bjkadron]

Ok.. Just checking but you would raise the rear roll center to decrease the roll in the back like a stiffer swaybar? Right mr. Shope? Or did I miss something?

[BillyShope]

Ok.. Just checking but you would raise the rear roll center to decrease the roll in the back like a stiffer swaybar? Right mr. Shope? Or did I miss something?
When determining the distribution of the lateral inertial force during cornering, BOTH the roll center height and the roll stiffness must be taken into consideration. But, when considering the fore-and-aft distribution of the driveshaft reaction torque, ONLY the roll stiffness distribution need be considered.

The asymmetric adjustment of the lower links has nothing to do with either the roll stiffness or the roll center height. That portion of the weight transfer taken through the lower links has a vertical force component. With an asymmetric adjustment, the vertical force at the right link is greater than that at the left, resulting in a torque on the axle housing which is both proportional to the driveshaft torque and opposite in sense. So, with the proper link forces (and, with the help of that portion of the driveshaft reaction torque which is fed back through the springs), it is possible to achieve full cancellation of the driveshaft torque for dragracing.

(Actually, for dragracing, you'd want 100% antisquat, so all of the torque necessary for cancellation would be by the link forces. The 100% antisquat would be an average of the left and right link adjustments.)
http://www.racetec.cc/shope

[JRouche]

Ok Billy, it seems you want to shoot down just about anyones ideas. Ok, so be it.

And as far as my original short PH bar and its lousy control of the rear end. It was more than just my seat of the pants feel. I saw the movement, and measured it in the shop before I even drove it. I actually DO measure more than I should. It was closer to1/4" with the full 4.5" travel. I was hoping to be able to live with it, I really didnt want to have to change it. I dont change something that works. Well not usually LOL But after some simple driving it wasnt gonna work.

The PH bar was pretty level. Its the standard art morrison bar used in their 4-link set up seen here, second clip down..
http://www.artmorrison.com/2006cat/34.pdf

But basically theres no way you can sit on your side of the computer and say my setup should work or prolly does. I built the car and drove it. Its right here in the flesh. So IMO Im the best source of info on whether it worked or not on my car. It didnt. And it wasnt my build, its the box stock setup from art morrison. But they did exactly what should have been done in the limited space.

I have yet to drive the watts link around, still wrapping the front end up. But Ill be more than happy, and honest to give my results. Seat of the pants or otherwise. Oh, and for otherwise I mean measuring the displacement of the rear end through its entire travel.

Well I did that already. And I have alot more travel now with the air ride. Not drive travel, but overall travel due to the additional air ride springs.

And with the watts link the rear end doesnt move side to side at all, not one bit. Mone doesnt anyway. And I really needed some decent control, my tire sidewalls are a half inch from my inner Q panels. So I put the rear end through all of its possible movements. And I do get some tilt of the wheels due to the rotation of the housing. But the tilt isnt bad and that was at 7.5 degrees of housing rotation which Ill never see on the road. But even at 7.5 degrees (digital protractor) of rotation (severe) the center line of the hubs were still only off from the center line of the car (yeah, I dropped a line and measured) by less than a 1/16". Meaning even with some extreme twisting and offsets the watts link was able to hold the rear end centered within the body.

And this idea that the arms on a watts link need to be horizontal is hog wash. Dont know where this comes from unless its engineers building on paper and they dont have a firm grasp on the way the links work.

A pan hard bar, yes. It is a two pivot link. So when you cross over the three or nine O'clock position you start going into the short side of the circle. So you will be shortening the arm length. Pulling the pivot points closer together and moving the rear end. So if its off from horizontal (dipping from the frame, pointing down) you will be pushing (growing bar) on the compression of the suspension and pulling on rebound. The rear end will move with the growing and shortening of the bar. And it gets worse the more the bar is angled.

The watts link has the all important key to the puzzle that takes all that shortening circle out of the equation. What is it? The center bell crank. Its the beautiful equalizer.

As one arm tries to pull the pivots closer together while it describes its curve during suspension travel the bell crank is like a moving pivot point. Think of it as the give and take equalizer. One side wants to take and the other side wants to stay put or take or give also. Ol Mr give and take bell crank will give to one and take from the other. If they both want to take or give she accommodates that too.

If both arms want to add to their length the the crank rotates counterclockwise. If they both want to shorten then the crank rotates clockwise. And whats cool is its completely variable. One maybe want not as much take than the other. The crank just rotates less.

If they are both moving but in opposite needs (one pulling and one pushing) the crank doesnt rotate at all.

The arms of a watts link do NOT need to be horizontal. The most important measurement? The need to be exactly the same length, eye to eye. And thats simple. And the bell crank needs to be of a sufficient length too. Six inches eye to eye is long enough.

I dont know. Build one, feel one, taste one. The watts link, if properly built is a pretty nice locating device.

So Billy.. Im kinda done with this part of the thread, I really want to see the Falcon up and going. Now that is what Im interested in. Its gonna be a really nice car when done. JR





Keep in mind that his goal is a "universal" setup with a minimum of compromise. When it is possible to achieve equal rear tire loading by simply switching the locations of a couple of bolts, the use of two swaybars would constitute both an unnecessary compromise and an unnecessary amount of work.


Without knowing the roll rate of the car and the size of the dip, I can't accurately calculate the lateral shift of the axle housing, but it would seem that a 2 inch drop of one end of the 24 inch Panhard captures the worst of conditions. This would result in a lateral shift of 0.083 inch if the Panhard was originally horizontal. Your seat of the pants is much, MUCH more sensitive than mine. And, since the upper and lower links of the Watts linkage operate through different angles, even a Watts would not have kept the axle perfectly located.

Since I consider its design perhaps the ultimate for a RWD beam axle car, I keep referring back to the early Jaguar C-Type, which managed to win Le Mans with a short Panhard.

He will never need a Watts with a '65 Falcon.
http://www.racetec.cc/shope

[BillyShope]

Ok Billy, it seems you want to shoot down just about anyones ideas. Ok, so be it.
Not at all! Nor do I seek to offend. But, when someone comes to the forum seeking advice and such an excellent example as the Jaguar C-Type is available, I believe that example should be offered.


And as far as my original short PH bar and its lousy control of the rear end. It was more than just my seat of the pants feel. I saw the movement, and measured it in the shop before I even drove it. I actually DO measure more than I should. It was closer to1/4" with the full 4.5" travel.
That's 3 times more than the example I gave, but I'm still not at all certain I could sense it. I have a friend who claims that Rusty Wallace could detect a 5 pound change in wheel loading, but I find it hard to believe. Still, I'm willing to concede that, to you, a quarter of an inch axle housing movement was easily discernible.



And with the watts link the rear end doesnt move side to side at all, not one bit.
And it shouldn't. As I pointed out, if the side links are horizontal at
some point in the suspension travel, the axle housing lateral control is essentially "perfect."[/QUOTE]


And I really needed some decent control, my tire sidewalls are a half inch from my inner Q panels.
I understand your concern.



And this idea that the arms on a watts link need to be horizontal is hog wash. Dont know where this comes from unless its engineers building on paper and they dont have a firm grasp on the way the links work.JR
No, Watt, himself, is the source of this "hogwash":
"The convexities of the arches, lying in contrary directions, there is a certain point in the connecting-lever, which has very little sensible variation from a straight line."
There is an animation of the travel...and the deviation from a straight line...available at:
http://en.wikipedia.org/wiki/Watt%27s_linkage
And, note that this is with the end links horizontal at one point. If this is not the case, the deviation is worse.

Suppose, for instance, that one 12 inch link is angled up at 5 degrees and the other down the same amount. This would result in an additional movement of about 0.090 inch as one link swings to the horizontal.

But, you don't need to worry about this latter effect, as it would appear that you have an excellent example of the Watt linkage in your car. If you fabbed it yourself, you did a great job and I can understand why you're proud to post a picture.
http://www.racetec.cc/shope

[LowBuckX]

Was at Quaker steak and lube yesterday sitting under a Nascar stock car used at Watkins glenn and sears point. That car has a Panhard..And I bet it works plenty well on the road coarse. Look to be about 42-45 inches about the same as mine will be...


Billy Im hard pressed to find a pic of the rear suspension of a c-class You have a pic.

[Bryce]

i have a car in my garage called an intermeccanica omega. It has a 3 link rear suspension with a panhard it has a offset upper link.

this was a holman moody deigned suspension from the 60's it has a italian body and ford running gear. I will try to get a picture today.

[Bryce]

JR

Its not that the bars need to be horizontal. They need to be the same length and parralel at some point during the suspension travel. I think the only way this is possible is to have the arms horizontal at some point.

for my application a long panhard will be easier to package. It will be 42" long.

[BillyShope]

Billy Im hard pressed to find a pic of the rear suspension of a c-class You have a pic.
Third post down:
http://www.hotrodders.com/forum/home-made-truck-arm-suspension-27086-2.html?highlight=Home-made+truck+arm

http://www.racetec.cc/shope

[LowBuckX]

Thant answers some questions. I found pics on individual parts but not assembled.

[Norm Peterson]

Third post down:
http://www.hotrodders.com/forum/home-made-truck-arm-suspension-27086-2.html?highlight=Home-made+truck+arm
The PHB in that C-Jag picture is certainly . . . ummm . . . unusual.


Norm

[BillyShope]

The PHB in that C-Jag picture is certainly . . . ummm . . . unusual.


Norm
It IS that. But, whatcha gonna do when there are no frame rails extending back to a big chrome rear bumper? It's essentially what dragracers do with their triangulation of the lower links of a 4link. Whatever works, I guess.
http://www.racetec.cc/shope

[Norm Peterson]

Leaving the bending of the PHB aside, I think that one of Mark Ortiz's fairly recent Chassis Newsletters addressed the topic of a lateral location link with plan view skew. From memory, I think it introduced some asymmetries of its own, which I wonder how they combine with the asymmetry of the upper longitudinal link. No opinion if good or bad, though I guess the C-Jag designers were mainly looking for a low roll center, and the overall result had to be at least better than somewhere between poor and evil.

Somebody over on Corner-Carvers has got the Chassis Newsletters hosted (or at least used to), and a search on that term should find the thread.


Norm

[BillyShope]

Leaving the bending of the PHB aside, I think that one of Mark Ortiz's fairly recent Chassis Newsletters addressed the topic of a lateral location link with plan view skew. From memory, I think it introduced some asymmetries of its own, which I wonder how they combine with the asymmetry of the upper longitudinal link. No opinion if good or bad, though I guess the C-Jag designers were mainly looking for a low roll center, and the overall result had to be at least better than somewhere between poor and evil.

Somebody over on Corner-Carvers has got the Chassis Newsletters hosted (or at least used to), and a search on that term should find the thread.


Norm
I get Mark's newsletters, but I must have neglected to read that one. (Hope he doesn't read this and stop sending them.) In a dragracing application, there would be no effect, so I must assume that Mark was considering the case when lateral loads are present.

As for the C-Type, it is my understanding...from communication with a Jaguar engineer...that very little analytical work went into the design's asymmetry. As the sketch indicates, they provided for a great deal of latitude as far as upper link offset was concerned. In discussing this with the Millikens, it would appear that mine was the first work to establish the analytical relationships between link positions and angles and the corresponding antisquat. This is not to minimize the work at Jaguar. As with the development of any project car, I'm certain they were pressed for time and felt that the proper solution could be achieved more reliably and quickly through testing.
http://www.racetec.cc/shope

[LowBuckX]

Billy could you take a look at my project at the link in my sig and tell me what you think. You did inspire me in part to do the offset upper link.

[BillyShope]

Billy could you take a look at my project at the link in my sig and tell me what you think. You did inspire me in part to do the offset upper link.
Looks good. Keep in mind that you can use the spreadsheet at Page 40 to adjust the lower links for equal tire loading.
http://www.racetec.cc/shope

[Bjkadron]

I'm still slightly confused, so another question. theoretically you could use the rear roll center height to control the oversteer/understeer characteristics like you can with a swaybar? And could you do this with a softly sprung car(for maximum mechanical grip) that uses swaybars to control the side forces?


When determining the distribution of the lateral inertial force during cornering, BOTH the roll center height and the roll stiffness must be taken into consideration. But, when considering the fore-and-aft distribution of the driveshaft reaction torque, ONLY the roll stiffness distribution need be considered.

The asymmetric adjustment of the lower links has nothing to do with either the roll stiffness or the roll center height. That portion of the weight transfer taken through the lower links has a vertical force component. With an asymmetric adjustment, the vertical force at the right link is greater than that at the left, resulting in a torque on the axle housing which is both proportional to the driveshaft torque and opposite in sense. So, with the proper link forces (and, with the help of that portion of the driveshaft reaction torque which is fed back through the springs), it is possible to achieve full cancellation of the driveshaft torque for dragracing.

(Actually, for dragracing, you'd want 100% antisquat, so all of the torque necessary for cancellation would be by the link forces. The 100% antisquat would be an average of the left and right link adjustments.)
http://www.racetec.cc/shope

[BillyShope]

...theoretically you could use the rear roll center height to control the oversteer/understeer characteristics....
No "theory" to it. Watch the NASCAR pit crews as they adjust the Panhard height to do exactly this.
http://www.racetec.cc/shope

[Bjkadron]

I hadn't thought about that... I think you just changed my plans.. :)
No "theory" to it. Watch the NASCAR pit crews as they adjust the Panhard height to do exactly this.
http://www.racetec.cc/shope

[Bryce]

what a great direction this thread is going, i like all this suspension design discussion.

[Bryce]

So I got my heidts subframe connectors (thanks route66, 10% discounts are nice) this will be my last building block for the 3-link. i have teh design done. Now I need to create a triangulated mount for the chassis mount for the upper link. It will tie into the SFC and the rear frame rails. This will be a very strong piece while adding minimal weight.

Packaging the panhard and the shocks behind the rear end and in front of the gas tank will be slightly challenging.

[PhillipM]

Old thread I know but this has really helped me on my rear 3 link design. Thanks guys!

[Bryce]

Phillip,

This was a good thread. I just need to start working on the 3-link for my car. Hopefully life will get out of the way for a little bit.

[PhillipM]

I decided to follow Billy's suggestions and am going to offset the upper link to the passanger side to cancel the torque of the driveshaft. Looking forward to seeing how it works.

[Bryce]

Hows it going Phillip?

Im officially starting the build design is done.

[Bryce]

FYI, I finished the 3-link. Its a bolt in design with A/S adjustment 70% to 150%. See my build thread for updated pictures.