True 3-link rear suspension

[Fake_Snake]

First time poster here, I have an 04 GT with the primary focus of AutoX, until I do some more upgrades and feel more comfortable with taking it to an actual track. I haven't ran the car but a few times but I consistently have issues with the rear suspension not allowing me to exit a turn under power, always lifts the inside rear. My current setup is pretty basic, as I don't have much money to throw at the car with everything else in life going on. I have H&R Race springs, tubular control arms with poly bushings (soon to be modified for heims on one end), MM CC plates, MM full length SFC's, SR Sway bars and racing seats with 5pt cage and harnesses to keep me from sliding all over, running 18x10s with 295s square setup. MM Panhard kit is on the FedEx truck as I type this.

I have done some research and cant find anyone that has converted the rear end to symmetric 3 link setup. I've seen the Steeda 5link kit but I'm not a fan of the upper link mounting to the side of the OE torque box, the evolution 3 link kit looks more like what I want but not a fan of their frame mount either, and I'm not sold on the PM3L. I also want something adjustable that doesn't hang down low like the Torque arm.

Is there a specific reason the upper link should be offset to the right or would a centered link offer more consistent Left/Right turning characteristics?
I'm currently targeting 65% antisquat for nominal position with adjustment means on both ends, is that a good target or should I go higher?

Once I get the Panhard installed I plan on cutting out the upper torque boxes to fab my upper frame mount, so I'm looking to get any advice I can from now until then.

thanks
-Randy

 

[blacksheep-1]

DO NOT use a Panhard bar with the stock style triangulated 4 link. There are multitudes of articles addressing this.
Also DO NOT use solid (type) upper trailing arms in a stock style suspension.

Look at this pic, you can plainly see that all the links are in competition with each other, it can't possibly work.
Even thought the PM3L is not the best way to solve this, it was used for years in NASA American Iron series for years, because they made you run the crappy 4 link. The bushings were non spec, which allowed you to run roll bar padding on one side, ( thereby negating that side) and allowing a PHB.

Well, apparently IMGUR has changed their method of sharing pics or some other BS, so here's a link

Junkyard Dog Build

So.. a quick look at the FAST rule book says this....M0 (Open Modified) Rules The Open Modified class (M0) is for exotic cars, and cars that exceed any of the above limits, but are otherwise street legal and on street tires. Cars that bump up from M1 also go to M0. For safety, doors, hood and...

trackmustangsonline.com

go to end of page 1

 

[blacksheep-1]

Here's another one

Four Link + Panhard Bar- Thoughts

Buying this Mustang and building the tube chassis for my Falcon has sent me down a rabbit hole of trying to understand suspension geometry, dynamics and kinematics. In trying to gain a better understanding of why the Mustang handles the way it does I made a quick sketch which shows the...

trackmustangsonline.com

 

[PatientZero]

If you're cutting out the torque box anyway it would make the most sense to just copy the S197 upper link. You could probably even get a S197 rear end housing and upper link to make it all work.

As for the torque arm. My exhaust scrapes before my torque arm and even then it has to be on a real janky ass road for that to happen. You could mimic a 4th gen camaro type torque arm that mounts to the side of the pumpkin rather than underneath.

 

[Fake_Snake]

@blacksheep-1 I was never planning on running the panhard in conjunction with the triangulated 4 link, and the parts of the PM3L I don't necessarily like is retaining the angled upper link and then having to reinforce the crap out of that torque box. I read every post on your junkyard dog build too, that would've been a fun car, sorry about your back injury.

@PatientZero thanks I'll try to dig up some specs for the S197 and 4th gen. Have you ever found yourself on a tight technical coarse and wanted another adjustment or has your torque arm just consistently worked great? From my understanding I would think the car would be a little unstable under heavy braking due to the very long arm
*Edit* Yes I'm basically wanting to mimic a S197 setup but with a longer upper link and the ability to adjust the angle on each end

 

[blacksheep-1]

@blacksheep-1 I was never planning on running the panhard in conjunction with the triangulated 4 link, and the parts of the PM3L I don't necessarily like is retaining the angled upper link and then having to reinforce the crap out of that torque box. I read every post on your junkyard dog build too, that would've been a fun car, sorry about your back injury.

@PatientZero thanks I'll try to dig up some specs for the S197 and 4th gen. Have you ever found yourself on a tight technical coarse and wanted another adjustment or has your torque arm just consistently worked great? From my understanding I would think the car would be a little unstable under heavy braking due to the very long arm
*Edit* Yes I'm basically wanting to mimic a S197 setup but with a longer upper link and the ability to adjust the angle on each end

There's no reason to cut up the stock torque box area of the car, the only time I've seen them damaged is with drag cars, it will pull the floor pan away from the side rail and also tear the mounts out,
Also my experience with a torque (truck arm down south) has been great, although it was with an autocross Camaro.

 

[Fake_Snake]

My reasoning for cutting the torque boxes out is simply for real estate purposes, having room to run a frame rail mounted crossmember with bracketry for attaching the upper link to the chassis. My logic is if the 3-link doesn't suit my fancy then the next option would be a torque arm which still doesn't use the upper torque boxes so they wont be missed regardless of the final setup. I read on a S197 discussion where a guy compared a 3-link and torque arm back to back and the 3-link outperformed the torque arm in cornering, further leading me down the 3 link path. Plus I have all the materials on hand so my only expense is free time to try it.

 

[racer47]

I prefer a 3 link for its adjustability. I'm at roughly 600 whp and 90-100% anti squat and it does very well on high and low speed autox. I've spent a long time and about 6-8 combinations before I settled in on what I have now.

Offsetting the top link does have an effect on left vs right corners. I don't rememeber the exact effect though. Oval track guys have experimented with it and some use it. But in general, I would want to stay centered for road race and autox.

A torque arm can work. They are non adjustable though. So its a bit of a gamble.

Its all really just geometry. Where is your instant center? How long is its length? How much does it change with suspension travel? In general longer is better, within reason, and minimal change with travel is better. Torque arms are good at these 2 things. But the front mount is low which leads to lower anti squat percents. 3 links, with adjustability and reasonable length arms, can get long instant centers and high anti squat percents and have low enough changes with suspension travel.

I've said it before on this forum but its worth repeating. Virtually all recent, purpose built, tube frame, road race cars with solid rear axles, have 3 links and a watts link. They could use a torque arm. They could use a panhard. They could use a triangulated 4 link. But 3 links dominate. I'm guessing its because of its simplicity and vast range of adjustment. Oval track guys also use 3 links but with a panhard because it makes changing the rear roll center height very easy and it has advantages for left only corners and softly sprung cars.

Very nice looking car. Good luck with it. If you're up for the cutting, welding, fabbing, I'd highly recommend a 3 link.

 

[Fake_Snake]

Thank you @racer47 Thats actually a higher antisquat number than I was expecting for autox conditions. I have zero sentimental connections to the sheet metal of this car so that's not an issue. I have the rear end measured and mapped out so with keeping the lowers as they are I have this design in mind which will yield AS%'s between 50-110

 

[blacksheep-1]

Very nice looking car. Good luck with it. If you're up for the cutting, welding, fabbing, I'd highly recommend a 3 link.

this...

Although, there is something to be said for NOT designing your own chassis, like, where does it end?

 

[racer47]

Fake Snake - (cool name btw), mine has a little slope up on the bottom links and tad less down on the top. That pushes the IC forward and up a bit for higher squat numbers. You may be good with 60-75%. I was not. My car is supercharged so in order to make use of the power, I kept upping the squat until it hooked. I'm paying a weight penalty for the power so I need to use all that I can to offset that extra front weight.

BS1 - It never ends. Thats racing. But it does slow down when you get fast enough and start winning. Then you maintain and fine tune. My car is an 06 that I bought in 2010 and have worked on it ever since. Its up on jack stands right now for this winters work. Not one piece of suspension is stock anymore. I've won 14 out of my last 18 races, in 20+ car fields. Last year a guy in a Vette won the last one. So now I need a bit more speed to push him back down to his normal 2nd place.

The quadrabind suspension sucks for racing. Although it was fine on the street for most guys. And I applaud the OP for his ambition to fix it and not band-aid it.


I've put many Vettes, Camaros and Mustangs to shame with this fairly stock looking, old school, stick axle car because I've fine tuned it to death. I have at 18 springs, 4 rear sway bars, 3 front bars, 3 upper rear arms, 2 pairs of lower rear arms and more that I've gone through to get it where it is.

 

[PatientZero]

@PatientZero thanks I'll try to dig up some specs for the S197 and 4th gen. Have you ever found yourself on a tight technical coarse and wanted another adjustment or has your torque arm just consistently worked great? From my understanding I would think the car would be a little unstable under heavy braking due to the very long arm
*Edit* Yes I'm basically wanting to mimic a S197 setup but with a longer upper link and the ability to adjust the angle on each end

My car has been primarily used for autocross. There definitely isn't time between runs to make adjustments and since every course is different it's kinda hard to set the car up to favor a certain type of course. I will say I think my car works better on very tight courses. The only brakes issues I've had is front grip due to a bunch of camber. No instability though.

 

[blacksheep-1]

Since we're going down this road,, I've always wanted to try this on a road course car.
What these guys call a "sway bar" really isn't, it does force the opposite to bite, so it sort of acts like one, but it's a solid piece. Drag cars are the one and only place the triangulated 4 link actually excels.. with a "sway bar" however.

 

[DaveW]

If you don't have an attachment to the sheet metal, cut a hole in the floor and run the 3rd link off a cross bar on your roll cage/bar. I always used a sliding panhard mount like below so you have infinite adjustability.

I am going to a TA on my S197 just because I don't want to cut the car up and the stock 3 link is pretty compromised, but in my experience a true 3rd link is the way to go for adjustability and also opens up a bunch of options for upper links with springs, cushions, shocks, etc. to further tune forward bite.

DaveW

 

[blacksheep-1]

If you don't have an attachment to the sheet metal, cut a hole in the floor and run the 3rd link off a cross bar on your roll cage/bar. I always used a sliding panhard mount like below so you have infinite adjustability.

I am going to a TA on my S197 just because I don't want to cut the car up and the stock 3 link is pretty compromised, but in my experience a true 3rd link is the way to go for adjustability and also opens up a bunch of options for upper links with springs, cushions, shocks, etc. to further tune forward bite.

DaveW

View attachment 72846

a lot of racing organizations will not allow you to penetrate the floor pan with suspension pieces

 

[Fake_Snake]

I think the only sheet metal I'll need to... relocate, will be the front most part of the spare tire tub in the trunk. A bar all the way to the main hoop would be way longer than needed, I'm just looking to match the LCA length for minimal pinion angle changes. I'm also thinking about slotting at least one of the mounts with a serrated block for real fine tune adjustments.

 

[blacksheep-1]

If you guys want to redesign your suspension then go for it, but seriously, how much forward bite do you need?

 

[Grant 302]

*Edit* Yes I'm basically wanting to mimic a S197 setup but with a longer upper link and the ability to adjust the angle on each end

Smart. My only suggestion would be to use rubber bushings, perhaps like OEM. Smaller, if the thought of that big one bothers you.

 

[racer47]

If you guys want to redesign your suspension then go for it, but seriously, how much forward bite do you need?

With all due respect......You are using a 3 link example to advise someone to not make a 3 link??

Plus, lifting the inside front is as much about roll stiffnesses as it is about forward bite.

 

[blacksheep-1]

With all due respect......You are using a 3 link example to advise someone to not make a 3 link??

Plus, lifting the inside front is as much about roll stiffnesses as it is about forward bite.

OK, let's start over..
This statement was what I was referencing
"I am going to a TA on my S197 just because I don't want to cut the car up and the stock 3 link is pretty compromised, but in my experience a true 3rd link is the way to go for adjustability and also opens up a bunch of options for upper links with springs, cushions, shocks, etc. to further tune forward bite."

now with regards to a 3 link on an SN95/New Edge
Most racing organization forbid piercing the floor pan with suspension links. Somewhere around here is a pic of an outstanding 3 link in an SN95, problem is/was the upper link had to come through the floor pan and connect to the roll structure.
Similar to this, but it had an adjustable bracket up front, which us why I suggested using a trailing arm for the 3rd link.

You can go down the rabbit hole of designing your own suspension, (and it's your car, do what you want) but you can also end up with so much frustration that it's no longer fun, unless you just like fabricating things and cutting them back off. I have done some of this, back in the 90s I designed and built my own kart chassis (basically one giant torsion bar) it was very rewarding, however, I would never in a million years want to do it again, I built 4 prototypes, (I used to bring a hacksaw and welder to the track) before I got it right. I really wouldn't wish that on anybody, especially since all the work has been done before, with the sn95 chassis.
The PM3L is a decent solution to the problem, I think some NASA guys are still running them, I would just run the truck (torque) arm and adjust on that, the mid 80 to early 2K Camaros used that system and it worked fine, They still use it in A Sedan.
The first thing to decide is, what does the rulebook say you can do?