3 Link, Stop me before it's too late...

[ITLBTU]

As my '69 Camaro project is getting deeper every day, I keep pondering the 3-link suspesion on the rear. Would it be a good idea to weld 2 pivot mounts on the top of the axel tube and connect it to a wish-bone shape uca with a single point to mount it on top in front. I'm planning on using heims on both ends. My idea is to do minimal cutting and hopeully make this almost completely bolt in while being able to get the geometry correct... Go ahead and school me...

[Damn True]

If you are considering a 3-link I would look to Lateral-Dynamics. The engineering is done and the results are solid. Yes the initial investment would be higher, but if you factor in your time required to go through the trial and error of developing your own system, IMO you'll be money and time ahead by going with the L-D version.

[ITLBTU]

If you are considering a 3-link I would look to Lateral-Dynamics. The engineering is done and the results are solid. Yes the initial investment would be higher, but if you factor in your time required to go through the trial and error of developing your own system, IMO you'll be money and time ahead by going with the L-D version.

That isn't an option for me. I'm quite sure that I can build my own for maybe a few hundred dollars, as apposed to over $6k. I also want it to be less intrusive as their's.

[baz67]

I am not exactly sure how you plan on doing this???? Where do you plan on putting the upper link? They way you are explaining the lower links it sounds like they will be above the axle and attaching to the body at a single point. If so, how do you plan on working around the driveshaft? What about lateral restraint?

[TLWiltman]

The trouble with not intruding into the passenger compartment on these cars is that you end up with a very short upper link (excessive pinion angle and anti-lift/anti-squat changes in suspension travel). What you're talking about is probably gonna result in some serious geometric compromises. Do you have any suspension design software (WinGeo, Suspension Analyser)? If not, you may want to start there. It's money well spent.

As far as a "wishbone" upper link. I don't really see the point. Three links work just fine with a single attachment point at both the rearend housing, and the chassis. So, I'm just not sure what you're trying to achieve. Maybe a bit more explanation on that might help.

I guess what I'm trying to say is. I admire the guts it takes to go your own way. But, at the same time, I'm concerned that there are many more wrong ways to build a 3-link than there are correct ways to do it. Just want to make sure you're being careful about this.:twothumbs

[Camaro Zach]

As far as a "wishbone" upper link. I don't really see the point. Three links work just fine with a single attachment point at both the rearend housing, and the chassis. So, I'm just not sure what you're trying to achieve. Maybe a bit more explanation on that might help.
wishbone style upper link will eleminate the need for an added lateral locating device (panhard bar, watts link, ect.)

[Beige]

I am not exactly sure how you plan on doing this???? Where do you plan on putting the upper link? They way you are explaining the lower links it sounds like they will be above the axle and attaching to the body at a single point. If so, how do you plan on working around the driveshaft? What about lateral restraint?
I think he was only describing the upper link.




As far as a "wishbone" upper link. I don't really see the point. Three links work just fine with a single attachment point at both the rearend housing, and the chassis. So, I'm just not sure what you're trying to achieve. Maybe a bit more explanation on that might help.

He's using the wishbone to locate the rear laterally.

I don't think it will be as simple as you think, ITLBTU. But by all means, keep working at it. Just get some verification before sticking it in your car.

[1971novaSS]

Hey buddy, Looks like you and me are going the same direction.

I am installing a 3-link into my 71 nova. I have 32 inch lower links and will have hopefully a 16-18 inch upper link. I have fabbed up the bracket to attach to the rear end pumpkin that will optimize the amount of "room" or space that you have to work with. My car will be very low so the other end of the link will be right behind the seat, literally RIGHT BEHIND IT!

I would try and persway you not to use the wishbone setup, im not sure you or I have the space. I am going to run a panhard bar for to locate the rear-end.


As far as a "wishbone" upper link. I don't really see the point. Three links work just fine with a single attachment point at both the rearend housing, and the chassis. So, I'm just not sure what you're trying to achieve. Maybe a bit more explanation on that might help.

EXACTLY, No point for wishbone! Use panhard.

I have the lower links finished and i am almost finished with the upper link. This will work with the STOCK rear seat in! I ALSO have a mini-tub as well.

And my rear-end geometry will be just fine. If you need any help or advice PM me and i can send some pics your way later on tonight.

And the 3-link is definently the way to go for handleing and rear end articulation ability. Oh and i will be using Hiems for now, But if you have the money use the Johny Joints. Johny joints have a 33 degree flex while hiems only have 22 degree. :6gears:

[David Pozzi]

wishbone style upper link will eleminate the need for an added lateral locating device (panhard bar, watts link, ect.)

Look at a 1959 Alfa Romeo Gullia Spyder rear axle, they use such a device. I believe it is a stamped A arm that pivots off the unibody just ahead of the axle and above the axle tube. It attaches to a bracket on the left hand tube with a good sized rubber bushing.

The Factory Five Kit Cobra uses a rearward offset housing bracket for the top link. It reduces the intrusion of the bracket into the cockpit.

[1971novaSS]

Dave, Im not sure i am understanding the information on the wishbone.

Either way you go, your over-all lenght will be the same. Just with three connecting points rather then two.

Wouldn't it deem more time consuming and complicated to fabricate two mounting brackets for the rear-end housing then it would if you just slapped a panhard on?

Or are you saying that you still will only have one connecting point to the top of the housing, and two connecting points to the front crossmember.

I just think the fabrication needed for the wishbone style either way would seem to be more complicated then just using a regular top link with a panhard rod setup.

And wouldn't the wishbone setup subtract the available rear-end articulation? Isn't that the purpose of the 3 link, to increase the movement of the rear-end, and ultimatley enhancing the handling of the vehicle? Once you add that extra link to locate the rear-end you just took away a good amount of available movement.

Maybe im going nuts? Definently possible. haha :hammer:

[baz67]

Alright I see the UCA now. I guess I missed it when I was trying to visualize what he wanted to do. However, that still does not explain how that setup is out of the way of the driveshaft. Also, with the UCA so low what about the SVSA length.

Unless I am totally missing what he wants to do how would the forward mount of the wishbone UCA be mounted without major work. Furthermore, if the wishbone UCA has double duty as the lateral restraint, how does that work? He states that he is using heims on both ends. I cannot visualize anything preventing the axle to move laterally.

[ITLBTU]

Actually, I was planning on attaching the 2 sided part of the wishbone uca to the axel tubes on either side of the cast housing. That way I can place the pivot point lower on the rear end, and the forward mount on the chassis. I'll attach a pdf of what I have so far. Ignor the short uca that is drawn. I need to verify the upper attach point on my Camaro yet. I plan on making bolt on brackets for the lca on the axel, and using the spring mount on the front. I do plan on using as long of a panhard bar to locate the rear. That would be adj for tuning. Both vet. and length for horiz. location.

[Derek69SS]

A wishbone will laterally locate the axle, so a panhard bar would not be necessary, and using one will create conflicting roll-centers.

[jerome]

here is a picture for those not understanding what he means:
https://static1.pt-content.com/images/noimg.gif
this method does provide lateral restraint, but in my opinion, not as good as the method below.


here is a better way to do it: connect the two points to a crossmeber, connect the point shown at the top of the below picture to the rearend.
the two points connected to the crossmember can be an axial bushing, but the single point at the top of the pic MUST be a spherical joint
https://static1.pt-content.com/images/noimg.gif

this does not reduce articulation in any way. the only way it would do that would be if the joint at the top of the rearend was a non-sperical joint.

here is something to ponder about: disregarding packaging restrictions, is a watts link any better of a lateral location device than a wishbone top link?

Jerome

[baz67]

Ok, that is what I thought. I would not put much faith in it doing a good job with lateral location. It seems there would be a lot of bending force that the single pickup needs to keep in check. But that is just me.

Yes, I feel a watts would be better because you can change RCH without having to worry about swing arm geometry.

[Steve1968LS2]

That isn't an option for me. I'm quite sure that I can build my own for maybe a few hundred dollars, as apposed to over $6k. I also want it to be less intrusive as their's.

$6k???

uh, thier kit is $3500 or so. Even if you build your own you will still need a differential :)

Anyways, good luck with the project.. I'm sure it will be a learning experience. Keep us updated!

[David Pozzi]

A wishbone will laterally locate the axle, so a panhard bar would not be necessary, and using one will create conflicting roll-centers.

I don't think there would be a conflict of roll centers because without a panhard bar there is no other "natural" roll center to conflict with like there would be with a leaf suspension. But the RCH would be several inches higher than a leaf or normal panhard/watts link rear.
David

[Ripper]

wishbone style upper link will eleminate the need for an added lateral locating device (panhard bar, watts link, ect.)

But it will also give you a very high roll center which affects handling. I would say a panhard bar or a watts link (with the spindle attached to the body, not the rear end) would be a better idea.


I was going to build my own 3-link but ended up buing an IRS instead. However, a three link is a very good solution. Try to attach the upper link in the center of the rear end. On top of the housing would be a good idea. Go for the same length as the lower arms and cut up the drive shaft tunnel. If you don't like the solution, hide it with a center console for the rear seat! ;)


https://static1.pt-content.com/images/noimg.gif
Is the upper link what I think it is? Some kind of delrinbased rod end? Where can I get those?

[Norm Peterson]

I don't think there would be a conflict of roll centers because without a panhard bar there is no other "natural" roll center to conflict with like there would be with a leaf suspension. But the RCH would be several inches higher than a leaf or normal panhard/watts link rear.
DavidWith a wishbone and the two other links you have two points of lateral constraint defined. One is the wishbone's single pivot, and the other is the virtual intersection of the other two links (which may be "at infinity"). That gives you the suspension's roll axis, and, at the intersection of this axis with the YZ plane containing the axle, the overall roll center. Adding a PHB or any other constraint will "overconstrain" such a system, which will then only work by virtue of compliances and geometric coincidence.

Mathematically, the three elements in a wishbone arrangement fully constrain the necessary four degrees of freedom. In this case, the wishbone is responsible for two of the four constraints instead of just the one constraint provided by a single upper link. Y-axis axle rotation (aka pinion angle) and lateral translation.

I agree that the combination of desired axle roll steer and driveshaft location will likely conspire to drive the roll center up to or above the top of the pumpkin.


Norm

[David Pozzi]

With a wishbone and the two other links you have two points of lateral constraint defined. One is the wishbone's single pivot, and the other is the virtual intersection of the other two links (which may be "at infinity"). That gives you the suspension's roll axis, and, at the intersection of this axis with the YZ plane containing the axle, the overall roll center. Adding a PHB or any other constraint will "overconstrain" such a system, which will then only work by virtue of compliances and geometric coincidence.

Mathematically, the three elements in a wishbone arrangement fully constrain the necessary four degrees of freedom. In this case, the wishbone is responsible for two of the four constraints instead of just the one constraint provided by a single upper link. Y-axis axle rotation (aka pinion angle) and lateral translation.

I agree that the combination of desired axle roll steer and driveshaft location will likely conspire to drive the roll center up to or above the top of the pumpkin.


Norm

Norm,
I was saying that there should be no conflict of roll centers with a wishbone upper link, and NO panhard bar or other lateral locator.
David

[atomicjoe23]

ITLBTU. . .if you are still looking to do this without buying a kit like Lateral Dynamics. . .check out the AFCO site. . .they apparently sell the necessary parts to make your own 3-link. . .I was watching Lou Santiago do this on a fastback Mustang that is going to be used to roadrace in the NASA series. . .I haven't checked the site out myself yet to see what is actually available but seeing him do it made me change my mind about my rear suspension. . .I'm now seriously considering going with the AFCO parts and doing it myself as well. . .I just have to check out the AFCO site and find the necessary parts to do it.

Good Luck!

[jerome]

But it will also give you a very high roll center which affects handling. I would say a panhard bar or a watts link (with the spindle attached to the body, not the rear end) would be a better idea.


I was going to build my own 3-link but ended up buing an IRS instead. However, a three link is a very good solution. Try to attach the upper link in the center of the rear end. On top of the housing would be a good idea. Go for the same length as the lower arms and cut up the drive shaft tunnel. If you don't like the solution, hide it with a center console for the rear seat! ;)


https://static1.pt-content.com/images/noimg.gif
Is the upper link what I think it is? Some kind of delrinbased rod end? Where can I get those?

yes, it is. its called a Johnny Joint. popular with offroaders because it is impervious to dirt and mud. you can even very big, heavy duty ones.

http://www.pirate4x4.com/tech/billavista/PR-Joints/index.html

heres a video:
http://www.currieenterprises.com/cestore/johnnyjoints.aspx

Jerome

[David Pozzi]

That A arm scares me, it is sure to snap off eventually, right at the top of the "A" if used on a car that corners hard. Some gussets would be needed at the very least, but even then, the weld at the bearing housing would be very highly stressed, not a good idea. OK for push/pull, but not left/right.

[ITLBTU]

The only reason I want to go to an "A" arm, or wish-bone for the top link is so that I can straddle the cast housing. It would be pretty hard to get a good weld on top for the upper link mount. It also gives me more room to mount the forward mount on the car vertically. I was crawling around under my car last night and I was getting a little depressed at how little room there is to work with. I don't plan on using the top link for lateral support. I will need a panhard bar.

[Norm Peterson]

The wishbone will provide lateral support, whether you want it to or not. Working at cross-purposes with a PHB will only hasten its failure in fatigue.

Can you fit a "real" 3-link, a la Factory Five's arrangement that moves the axle pickup to the right of center and behind the axle centerline?


Norm

[Mean 69]

We hear groans about our kit from time to time, in terms of cost, and also in terms of packaging requirements necessary to clear the linkages, etc. And that's fine, the Lateral Dynamics package is not for everyone, and we know that and don't try to push it down folks' throats, or make broad claims about it stating that it is the end-all setup. But, when you try to attempt what we have done with our package on your own, you soon find out that's it's not so trivial. Even more challenging was to put it into "kit" form that can adapt to the factory chassis and construction tolerances, while still being user-installer friendly enough for a serious enthusiast to install at his/her own place.

There's not much room, at all, for the upper link with a factory floorpan in uncut form. In fact, if you aren't willing to cut it to make room for the upper link, I'd suggest looking at another approach, because the compromise you would need to make to the upper link length would seriously hamper the inherent benefits of using a 3-Link to begin with: it'd have to be REALLY short, and short isn't good. The math says so, and so does reality, sorry.

The challenge of using a cast center is also a really hard thing to overcome. That's why we went with the 9" Ford style center section (as well as it being the most popular setup to get parts for, being very strong, and not as heavy as some of the others). It can be done with a cast center, but it's not for the weekend guy, this would have to be seriously engineered to handle the loads, with sticky tires they can be pretty darned high.

Nice to hear that you aren't looking for lateral support from the A-arm setup, it "can" work if the right design and components are used, but frankly, folks don't do this approach because it's far easier to just use four links. I'm firmly with David, that particular piece pictured is failure waiting to happen. I'm with Norm too, using it with another lateral restraint will introduce big time bind, and again, something will break.

Best of luck, keep folks posted!
Mark

[1971novaSS]

The only reason I want to go to an "A" arm, or wish-bone for the top link is so that I can straddle the cast housing. It would be pretty hard to get a good weld on top for the upper link mount.

I will be tacking the mount i fabricated for the top link onto the rear end housing. Then removing the rear end and having my brother(multi-certified welder) Weld it. But i will not be using the A arm configuration.


I was crawling around under my car last night and I was getting a little depressed at how little room there is to work with. I don't plan on using the top link for lateral support. I will need a panhard bar.

Yea, i have been crawling around for many, many hours trying to build this stinking rear-suspension. And im not a "small" guy either. Its best to remove the rear-end for the final welding and paint after everything has been mocked-up and ready to "WORK".


That A arm scares me, it is sure to snap off eventually, right at the top of the "A" if used on a car that corners hard. Some gussets would be needed at the very least, but even then, the weld at the bearing housing would be very highly stressed, not a good idea. OK for push/pull, but not left/right.

DAVE, Bingo! If this is going to be a differential locating device then it better be much stronger then that one in the pics. I just wouldn't trust an A-arm to withstand the force exherted on that joint/weld when taking an agressive corner at high speeds.

I am going out to finish up the upper link right now, The sun is shinning. Gotta get my but off this computer.:throw: I will come back with pictures.

[ITLBTU]

The wishbone will provide lateral support, whether you want it to or not. Working at cross-purposes with a PHB will only hasten its failure in fatigue.

Can you fit a "real" 3-link, a la Factory Five's arrangement that moves the axle pickup to the right of center and behind the axle centerline?


Norm

I think I might be waking up here... I thought that there would be no lateral support because the front could still swivel. I think I undersand now. With out the PHB the rear could sway side to side, but with the wish-bone upper link it would bind because it doesn't have the same motion. I guess it would be like placing a cast on your elbow. Your arm would still move but not the same. I wonder if a mount could be made that would bolt on using the rear-end cover bolts? Would there be too much force for that? Does the pivot point have to be on the center line of the axel F/R to be effective?

Another thought would be a torque arm setup. Would that be bettter than leafs?

Mark, your design is the inspiration for my desire to do this. I think your kit is worth every penny. I would love to be able to buy your rear kit, but with with a wife, a teenager and a baby to feed, and another on the way, you'll be retired before I can afford it!

[atomicjoe23]

[quote=ITLBTU] I wonder if a mount could be made that would bolt on using the rear-end cover bolts? Would there be too much force for that? Does the pivot point have to be on the center line of the axel F/R to be effective?quote]

This is the type of mount that I saw Lou Santiago use on MusclecarTV on the road-racing '65 fastback that he's building. . .he said he got all the parts (for the entire DIY 3-link) from AFCO Racing, but I'm having difficulty finding them on the website. . .I've written two e-mails to AFCO Racing now about it with no response yet (kinda of discouraging when a company doesn't respond to your inquiries about their product) and I've now sent one to MusclecarTV as well since I haven't had any luck yet with AFCO themselves. . .if I find it I'll send you a link. . . .

[Mean 69]

I wonder if a mount could be made that would bolt on using the rear-end cover bolts?

Not by themselves, unfortunately. It would have made life a LOT easier for us!


Another thought would be a torque arm setup. Would that be bettter than leafs?


A well done Torque Arm will beat the snot out of all but the very best leaf setup, probably ANY leaf setup. This is the suspension of choice for most of the folks running in the American Iron series, where the rules tend to favor the later fox body Mustang cars. The cars haul tail to put it mildly, but the ability to tune the suspension geometry is not as liberal as a 3-Link setup. Further, a well done Torque Arm will outdo a poor 3-Link, as demonstrated by one of the prominent T/A Mustang suppliers: they replace the 3-Link setup on the newest Mustangs with a Torque Arm setup, allegedly with tremendous performance improvement. If you use a stick axle, and can't fit a good 3-Link, T/A is the next best thing in my opinion. This is a really good alternative for folks that are not willing to cut the cars up too, we get a good number of requests for folks in this very situation. And, we're listening. And taking action. :evil:

For off the shelf type stuff, AFCO, Coleman, Stock Car Products and other circle track suppliers have a good amount of stuff to help out. Keep in mind, circle track cars only have to turn in one direction though, proceed with caution. As always, your mileage may vary greatly.

M

[Norm Peterson]

[quote=ITLBTU] I wonder if a mount could be made that would bolt on using the rear-end cover bolts? The whole cover assembly might be made to do double duty and incorporate an upper link attachment. Buick, and later Kirban, with their GNX traction arm arrangements did something rather similar. I can't really suggest directly using the Kirban piece for a 3rd link upper attachment at this point, as I have no idea whether it would survive in leakproof fashion with only one of the two attachment points loaded (and loaded somewhat differently as well).


Norm

[shmoov69]

progress pics.............

[jerome]

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

[1971novaSS]

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

That thing looks like a leaking disaster waiting to happen.:lol:

The more i read about the wishbone upper arrangement, the more i like the 3-link.

But a 3-link is not the easiest thing to fabricate. As i have found out.

[ITLBTU]

This is why I post my ideas here. I'm now leaning towards a de-coupled torque arm.