Does anyone from the site know anything about 3-links or direct me to someone or somewhere that I can get info on building one for my 69. I`ve tried on protouring.com, but seems someone over there has it all in wraps and no one will give me much info. Thanks in advance

Herb Adams has some info in his book.
One of the Steve Smith Autosports books may cover three link design.
Three link is a good system, just watch wheel hop under braking. A decoupled three link is supposed to be even better according to Adams.

I think a pretty good three link could be done on a Camaro by running lower links forward to the leaf spring brackets and one top link to a mount just above the driveshaft tunnel, but I don't know the exact height of the top link position.
Of course you need a panhard bar.

A good circle track builder should know what to do.
David

Thanks for the reply David. Do you know if I could run the lower links with a rubber/poly bushing or would it have to be heim ends? From the limited info I`ve been able to find on 3-links, it seems the upper link uses heims and the lower seems to suggest rubber/poly. Also, do you have any idea on how long the upper link would have to be? I know of someone in the circle track world, I`ll have to go hit him up for some info too.

Herb designed a three link for his kit Cobras, I believe it has heim joints on it, I don't recall how they said it rode but it didn't seem to be an issue. If I see Matt Adams I'll ask him about the ride quality. The street rod guys use a rod end made with polly bushings in it. It doesn't look like a rod end, just a threaded T shaped deal.

I have a friend who made a McLaren Coupe with those on the rear suspension to smooth the ride, but again I didn't really hear if it had good results. In general, I'm not fond of polly joints because polly is a sticky material under pressure.

I have also seen a Vintage Trans Am Camaro built on a car Penske had something to do with, maybe he donated an old car or parts. It was built by a school near Penske. It had a three link rear suspension but it was pretty crudely done as far as the looks of the bracketry.

I've spent some time searching the net for info but there isn't much to read on three link systems.

The guy on PT.com said he will have more to say when he get's his system working.

Adam's book suggests a minimum swing arm lengh of 42 inches to prevent rear wheel hop.
He suggests link brackets off the rear axle be around 5" long from axle center to lower stress load on the rod ends to an acceptable level. Run the lower links level to the ground, incline the upper link downward to intersect the lower link line intersecting at least 42 inches forward of the rear axle center. In his illustration, the upper link is about as long as the lower links. Maybe you can cheat the upper link length though amd make it shorter.
Factory Five Cobras have a three link with the upper link offset to the rear, the upper bracket off the housing goes rearward to keep the link long without having it reach as far forward as it would otherwise. http://www.factoryfive.com/table/newsltr/newsltr02/threelink.html


David

David, in the link you provided. I see the upper link isn't in the center of the rear end. Do you think this could be a problem?

I think it would offset the lift moment to one side a bit if the upper link runs straight ahead.
The right rear wheel tends to lose downforce due to axle torque, so perhaps offset to the right of the link would help to counteract that?

Just thinking out loud a bit, I haven't really given it a lot of thought. you might be able to angle the upper link front anchor to the left to correct for it, but it might cause other problems.
David

Factory Five Racing was one of the first places I looked when I started researching 3-links. When I first looked them up, I noticed that I don`t see the 2 lower links in their kit. They do have, however, a T-shaped looking bracket. Is that bracket part of the framework or is it more of a critical suspension part. What are the longevity issues of heim ends?

Adams says 3" to 7" is the range of link attachment points from center of housing. 5" is most common.
If you go shorter the loads on the links go way up and rod end life is shorter.

On a heavy car like a Camaro I don't think rod ends will last years and years. Spherical bearings would be better but will require a housing to go in. Maybe you could use spherical bearings in fabricated lower links and HD rod ends on the top link.

Maybe delrin bushings on the lower links would work but I'd check for enough freedom of movement.
David

Thanks David. Looks like I need to buy Herb Adams book and start from there.

the 87 Buick GNX had a 3 link setup that used a custom differential cover to mount the middle link- and the link was offset to the passenger side a couple of inches to even out the weight that pushed down on each rear wheel under power. it counteracted the tendency of the axle to want to lift the right rear tire under power when the turbo boost hit hard, or so i've read. it also apparently made those cars hook HARD- even on 50 series 16" tires.
http://home.att.net/~buickGNX/GNX/media/rear_lift.jpg
http://home.att.net/~buickGNX/GNX/media/rear_diagram.jpg
too bad no one makes a kit based on those parts for all those traction limited 78 and newer G bodies running around out there. but i have read that someone makes a reproduction of the GNX diff cover with the link mount on it- which would work on an old Camaro 10 bolt housing as well, since the turbo Buicks used the 8.5" rear end. you're on your own if you have a 12 bolt or a 9 inch rear, tho. then it would just be a matter of making all the links and not worrying about if the center link mount on the housing is sturdy enough.

Wouldn't the GN suspension be more of a "torque arm" suspension? Since there is a bottom link also, it's no longer only 3 links.

The GNX suspension uses a torque arm, i.e. the arm isn't free to move relative to the rear axle, like the 3rd-4th gen F-body cars. I have no first hand experience as to how well it works, but Kirban's was reproducing the entire system as of a couple years ago.

This might sound like a stupid idea AND it darn well might be, (but I have to ask after looking the GN rear set-up over real good), if anybody knows of this has ever been used??

Use quarter eliptic springs SOLID mounted to the frame at the thick ends and triangulated in some like the "truck-arm" set-up, (one on each side towards the front), and then rubber mount the tapered ends to the rearend just SOLID enough so they can pivot to allow driveway entry and such.

Then add a bottom link that would pivot on both ends in rubber that was the same length as the springs so it rotated the same as the rearend would.

And last, add a, (as close to horizonal as possible), panhard-bar for side movement and finally two good shocks..

Seems to me that there would be no wind-up at all but there would be good suspension "working ability"..

Super simple if it will work!!!

What does everybody think??

pdq67

There has been alot of automobile manufacturers in the past that used different variations of the 3-link style suspension. I have come to gather from my research that basically none of them live up to what I would like it to. Ford has the 3-link in their lightning trucks and I believe a form of the 3-link in the mustangs now.
I am running the Currie aluminum housing 9 inch rearend, so any type of setup that requires anything to hang on the differential case is out of the question. Thanks for all the info gentlemen. I am going to go at this on my own and try to get some help from some local circle track guys as David suggested.

PDQ, I would imagine if you're going to all the trouble to eliminate the leaf spring wrap-up by only using 1/4 of it, you might as well replace the two 1/4 ellipticals with trailing arms, install coil-overs, and voila, you're back to a traditional 3-link design. The bending moment at the rigid mounted end of the elliptical sections would be huge, and because they're so short, you'd get minimal suspension travel. Just my thoughts--if I'm understanding you wrong, lemme know!
Hey Makoshark, the big issue with a 3-link is the compromises most manufacturers make to package it underneath a car. The third link needs to be long enough that, in most cases, the chassis-mounted end protrudes into the back seat area. Too short, and the pinion angle rotates too dramatically through the travel of the suspension. While a 3-link is a great setup if it's designed properly, a torque arm will probably require less cutting and modification of the underbody. Let us know how it goes!

I agree the torque arm is easier to package.
An aftermarket Moser 12 bolt housing made for third gen Camaro upgrade might be the best way to put one on a first gen Camaro, it has the TA mount holes cast in.
I checked my Race Car Suspension Engineering book by Millikan and Millikan. The upper link offset to the right as used in the Factory Five rear setup is as I said above, will offset rear axle torque but may cause a small jerk when you let off.

If you have one of the GM "Chevrolet Power" books, look in the back section, there is some info taken from the Millikan books there.

I found this:
http://www.talkaboutautos.com/group/rec.autos.sport.tech/messages/21945.html
http://www.howeracing.com/Chassis/Index-Rear.htm

Here is the 2005 mustang three link rear:
http://www.rsportscars.com/foto/05/mustanggt05_detail.jpg

David

[ 06-24-2004, 12:02 AM: Message edited by: davidpozzi ]

Mako, in the link David posted above, the upper link mounting location doesn't mount to the center section, so you still have that option.

Also, for those running a 10 or 12 bolt. I would think one could make an upper mounting bracket for the upper link location by making a bracket that mounts to the backside of the case. If you used an aluminum housing cover, and then used studs in the upper cover bolts, the bracket could then be attached to the top of those studs, with nuts to secure.

There is actually a lot that goes into designing an appropriate 3 link suspension. By the way, I think I am the guy that you may have referred to on ProTour.com. Sorry for the lack of disclosure, but there are some very valid reasons for not giving all of the details. Going to a circle track guy is a good idea, they use these extensively in short track racing. Just make sure he knows you want to turn in both directions!!

The three link is a darned good solution for a road racing type application, but it really depends upon the kinematic design. The advantages are tunability, simplicity, lack of bind in bump/roll, and unsprung weight (though this is probably not a huge advantage given the already huge weight of the differential itself).

The trick is to get an appropriately long Side View Swing Arm Length, which is essentially the convergence point of the upper and lower control arms, as viewed from the side. As David pointed out, the downside of this being too short is a tendancy for brake hop, which is a really not-nice thing. The orientation of the lower control arms has a big influence on roll steer, which is a tendancy for the rear axle to actually steer the rear of the car in roll. There are many other things to consider as well, but that could take up quite a lot of space here.

I'd be really cautious about bolting on a bracket to the rear of a ten or twelve bolt housing to act as the upper link mount. I am not suggesting at all that it can't be done, but the decision should be based upon a true engineering analysis. The issue is that there will be a large amount of tension (strain) on the mount under acceleration. Under braking, there won't be as much due to rear braking bias (~30% of the total braking force). If you are going to try this, defintely consult an ME for help on the mount.

One more thing, as mentioned previously, a three link will most likely require intrusion into the passenger compartment, but it doesn't necessarily mean that it will be obnoxious.

BTW, the GN link system that is shown on this thread is a Torque Arm setup. This particular system probably launches like the dickens, due what looks to be a significant amount of anti-squat (really short T/A). I'd be interested to hear if there is a brake hop issue with this system though, the SVSA looks really short. I personally don't know anyone that has this setup, if anyone does, I'd be interested in feedback on this suspicion.

Mark

Mark,
Thanks so much for your input to this discussion. graemlins/thumbsup.gif
What would you hope or think a three link would do better than a torque arm?
It seems one of these two are the "best" for a Camaro.
David

[ 06-25-2004, 09:36 PM: Message edited by: davidpozzi ]

I think that either a Torque Arm, or a three link can be made to work exceptionally well on these cars, but both require some compromises that each individual would need to think about for their application.

The Torque Arm solution is well proven with many of the late model Mustang folks, there are two aftermarket producers in particular that have great products that work extremely well. However, the design approach both have taken is to sling the T/A under the driveshaft, which has a potential negative impact on ground clearance. With the Torque Arm, the Side View Swing Arm is defined by the length from the forward mount of the T/A to the centerline of the axle. The literature suggests that a minimum SVSA is 42" (from Herb Adams, or 60", per Milliken) which means that the arm itself has to be pretty long. Because of the way the system works, pretty much all of the torque of the drivetrain is reacted through this arm, so it has to be very strong. Strong plus long, equals heavy. Doesn't have to be prohibitive, but is clearly a significant issue to consider in the design. Torque Arm suspensions can be made to have very good anti-squat, roll steer characteristics will be largely impacted by the orientation of the lower control arms. I love the idea of the torque arm, the decoupled version looks even more appealing, but the packaging is the main turn-off for me, I scrap just about everything with a slightly lowered late model Camaro, reducing ground clearance is not something I wish to compromise.

The three link has its share of downfalls too, most notably the fact that the upper link will need to reside above the driveshaft (centered, for road racing, neutral reactions) which means getting into the passenger compartment. One benfit of the three link is that you can get a really good SVSA, because in this case it is defined as the intersection of the upper and lower links in side view, NOT the physical length of the arms themselves. Through adjustment, you can get a larger range of instant center locations than you can with the T/A, so it is theoretically more tunable. Potentially lighter too. Both are simple solutions, and both systems work really, really well.

For me, it just seems like the Three Link is the best compromise of performance versus packaging. I have tried to fit a Torque Arm under a 65 Mustang (along the side of the driveshaft, not under it), and though it fits, it is really tight and requires packaging compromises that I don't like. If you read Herb's book, the project car that they built and pictured had provisions for both a three link, as well as a T/A (a Sathcel link too, for that matter), but there were no results from which system he liked better, on that car. All cars will behave differently, but it would have been really interesting to see which the car worked better with.

Mark

Mark,
Thanks for your thoughtful comments. Every time I think about three link suspensions, I come back to the torque arm as an easier alternative because there is no upper link, but I haven't installed a torque arm, so I haven't seen first hand the packaging problems associated with them.

Herb's son Matt uses a three link in their Cobras and they say it's better than the independent suspension version they sell. The ind version is the late model Ford unit.

The three link version allows more anti-squat because the engine torque acts through the links to plant the rear tires. the independent rear has the housing bolted to the chassis and torque is reacted through it's mounts, but not as effectively.

I don't recall any mention of the satchell link the last time I was there.

Matt reciently built an aluminum block 427 SB chev powered Cobra with three link, quite a rocket!

There is a C prepared 10 time SCCA national champion autocross winning 70 camaro that uses a torque arm that is about half the length of a GM torque arm. It still uses leaf springs due to the rules.
David

OK, so I'm a month after everyone else that was a part of this thread. It turns out, my brain has just started running on what to do next and the rear suspension is in my sights.

The person who put my rollbar and subframe connectors in owns a circle track car and his whole summer is generally occupied fixing circle track vehicles. I bounced the idea off of him on how to do a 3 link set-up. He suggested that the distance from center of front spring eye to center of axle is a reasonable starting length for the lower links. (This distance is 25 1/8 inches.) He also suggested that the upper arm be about 2/3 the length of the lower links.

I was then poking around the S&W catalog and wondered why not just take their prepackaged 4 link setup, put the frame rails as widely spaced as possible to get the desired tire clearance and call it a day. It turns out their links are about 23 inches from center of front eye to center of axle. Obviously a panhard bar and coil overs would be part of the package.

So what is the consensus on this? Would the links be long enough/strong enough? Would one be better off with a three link?

Ed

Strange timing, I hadn't checked in until this morning, also about a month out!

The main difference between a parallel (think top/plan view) four link, and a three link, is that the upper links are replaced by one link (obviously). In higher roll angles, this can/will reduce bind in the the system relative to the four link setup. Because the loads that are seen by the two upper links in a four link setup would be seen by only one bar in the three link, the upper link in a three link needs to be stronger on a relative basis, including the chassis pickup points.

Beyond that, the real differences would be the placement, length, and angles of the bars. By putting the LCA's in the near stock configuration (i.e. front spring pocket, and some form of bracket under the differential), there will most likely be a pretty good upward slope, which for a road race car is bad. The reason for this is that the rear "roll axis" will be biased towards a roll-oversteer tendancy. Dropping the front mounts down to be nearly the same height as the rear mounts would improve this aspect, creating a more neutral roll axis, but this would limit the amount of anti-squat you could dial into the car, limiting the ability to really get after the loud pedal out of turns. Everytime you poke one constraint, you very likely compromise another, things are very inter-related.

If the car is going to be a street car, you can probably make the readily available four link setups work pretty well with tuning, etc. If it is going to be a track car, then you really want to be cautious about how you arrange things, bad things can happen really fast at speed, and safety (in this case through a predictably reacting suspension system) needs to be one of the very first concerns.

You are correct, at minimum you will need a long PHB to locate the rear laterally, and it will need to be STRONG! The track bars, and short PHB's that are generally offered with the street-strip packages are totally unsuitable for a performance cornering application.

Mark

BTW: Davd, I tried to contact Matt at VSE, but could not seem to get through. If you have a good contact number for him, could you please shoot it over to me? I am interested in a part listed in Herb's book that they may be able to supply.

I am trying to visualize my car while sitting here at work. The centerline of the axle is at about 13 inches. The point on the subframe connectors where the new rear frame rails would attach is about 6 inches off the ground. If we went with the 5 inches from axle centerline to LCA rear mount hole suggested in a previous post, the front hole could be 1 inch up and still be horizontal. So far so good.

To do a 3 link, I could weld a bracket onto the housing of the rear (a ford 9"). A crossmember/bracket would have to be welded to the new frame rails at the right postion to give some angle adjustment. No problem I can see doing this.

The outstanding questions to me are: Is a 23" LCA long enough? Is it worth it to go through the trouble of doing a 3 link instead of the 4 link? Is the packaged 4 link set-up strong enough?

I don't expect to road race this vehicle, but do enjoy spirited driving on the road. (I may do Solo 1.) I do take the car to the strip on occasion and would like some serious hook capability, which I do not have now (but I also want to keep the low stance I now have).

Ed