I know some of you guys absolutely hate the idea, and I realize for the road course and corner carving guys it's not a good fit.

I keep wanting to do something like this, so I can ditch the torque arm setup on my 9". I know @five7kid ran the g-force setup years ago, which is no longer available.

I've seen these photos a few times. Seems like it would be fairly straight forward to build this.




I have an old set of founders LCA's I thought about welding some chassis tabs on, and the same with the 9" tube ends.

 

Looks like the fastener attachment point for each is about 20% the distance from axle centerpoint of a stock forward torque arm bolt. So, worse pinion amgle control. If set up ladder style and rigidly attached LCA to bracket attachment , rougher ride with no apparent improvement that could be named.

9s are steel and take to welding unlike cast.

Have fun.

 

I think pinion angle adjustment isn't too much of an issue. You'll be able to rotate the axle significantly in either direction.

The issue I see is getting the instant center right. Generally speaking, with ladder bars you want a longer bar since your intersection is fixed.

I've been learning a lot about suspension since I started getting into model A rat rods and tube chassis race cars. It's nice having a blank canvas on those cars because you can fabricate the frame and then make the body work. With a unibody production car the options are a lot more limited.

There are things I absolutely do not like about having the torque arm on the 9". This isn't a new idea, I've been going back and forth on this for over a year. I've thought about mini ladder bar or unequal four link. Both have pros and cons.

This is also a street/strip car.

 

They did free up a lot of space under the car, particularly for routing exhaust.

That's about the best you can say for them. All the "cons" already mentioned were very much in play.

While pushing the car off the track after breaking something else, one of the older track guys said to me, "That's the first car I've ever seen lift the rear tires off the track at the hit!"

Soon after the car got a torque arm. After 3 tries, it had one that actually handled the abuse a stick car can dish out. I sold the car soon after that (2013).

Last year, a race car builder and highly successful drag racer told me about my current 3rd gen, "If the factory hadn't offered the torque arm setup stock, your car wouldn't be NHRA legal."

 

Why did it lift the rear tires? That is odd.
I was doing some calculations, and I believe the factory length torque arm ha about 37% anti squat. To get the same thing out of a four link it can be done with a 19.25" bottom link and a 10" top link, 6" apart. I was thinking that there should be enough room to mount a top hanger kinda where the seat belt bolt is.

The steel in that area seems strong enough.
I was trying to calculate the mini ladder bars but I'm fuzzy on how it differs, if at all, with the top angle going to the first third of the bar rather than the pivot.

 

A ladder bar setup like that doesn't allow the rear to deflect differently on the 2 sides. It can't. Doesn't matter if it's a home-brew job like the pics, or something manufactured elaborately (*cough* Lakewood *cough*), or what, or how long/short the various sparts are, or anything else. Each one is a triangle, and as such, the lengths of the 3 "active" sides - lower rear mount to front mount, upper rear mount to front mount, and lower rear to upper rear - has a fixed length. If the 2 sides of the suspension try to deflect differently, some one or more of those triangle side lengths HAS TO change. That's kinda how it works in drag racing... it forces the rear of the car to stay absolutely level, or at least, at the same level as the axle. However, that advantage on the strip, is not sustainable on the street, primarily because of the unibody, which lacks the strength of a tube chassis. On the street, it's GONNA break SOMETHING, and it won't take long.

The instant center is the same no matter how the bar is constructed, since it's based off of the angles created by the contact patch of the tires and the front ladder bar mounts. It doesn't change by adjusting those links. All those would do, is change the pinion angle, which will then only be "right" at exactly ONE point in the rear's travel.

Altogether IMO not A Good Idea, UNLESS: it's STRICTLY a single-purpose, trailered, strip-only car; AND, the chassis is already reinforced to the point that the forces exerted on it by that setup will be COMPLETELY removed from the unibody.

As far as building it, a piece o cake. All you need is the 4 tabs to weld to the axle tubes and 2 to the LCAs, which can be easily cut from flat stock. You could even use a local water-jet or laser shop, or emachineshop.com or some such, and come up with something that looks professional. The axle tubes are steel, not cast-iron, so they weld quite easily. Although, if I was building it, I'd make the link as close to the full length of the LCA as I could, since the restraining force that it exerts on the car, will tend to make the straight section in front of the front link mount, try to bend. A side of a triangle resisting a force tending to change its length is MUCH stronger than a straight element trying to resist bending. The limit to that of course is the clearance between the top of the LCA and the unibody right above it.

I'd suspect that five7's rear hopped due to the sheer violence of the hit making the tires literally dribble like a basketball. I don't "know" that of course; I never saw it; butt that would be my best guess. I've seen that elsewhere when a car is set up with too much "anti-squat".

 

Rather than a ladder bar, what about a triangulated four bar like this:



Everyone tries to do the upper links at the top of the housing like a gbody or fox body, but something like that, assuming it didn't crash into the sway bar mounting, could work I'd think.

 

That's just a triangulated 4-link with the upper links having less leverage on the axle trying to "twist" than a traditional one. A suspension of that sort needs to look like a trapezoid or the like from the side, with the 4 corners at the ends of the arms. That looks basically the same as a stock 4-link, except that the centerline of the axle is higher up on the rear vertical plane of it, than usual, in which it's more or less centered. To get enough vertical distance between the arm mounts on the axle, with the uppers that low on the housing, the lower arms are almost scraping the ground to get the leverage back. Would be impossible to locate the IC correctly otherwise.

On A or G body, the reason the upper link at the axle end usually has to be raised quite a bit, is to bring the IC to somewhere under or within the car, where it needs to be. Stock, it's usually several feet in front of the car, or sometimes even behind the car. Not too different from how messed up ours come from the factory in that respect. Butt that's a function of their stock chassis design, specifically, their limit on how high up on the chassis the front upper arms are mounted. And it has to be that way so that the pinion stays at a reasonable angle throughout its articulation. With 4 equal length arms and the upper and lower arms parallel, the pinion angle with the ground, and the transmission shaft, would remain constant, as it more or less needs to. There's not enough space under a marketable car for the upper mounts to be up that high and still have a rear seat though; to be a "useful" consumer product therefore, the arms need to be unequal and/or not parallel, and the IC out in the ozone. But to put anything like that in one of our cars, looks to me would require carving ALOT of the rear floor pan out.

The IC in that kind of system is at the point that a line drawn through the upper and lower arms, viewed from the side, intersects. You'd typically want it to point at the car's CG when comfortably within its adj range, which would be "neutral"; then you can tune it from there. The most popular place to imagine the CG being is the shifter ****. I'm sure it's never EXACTLY there, but that's close enough to at least get a visual, at least in most cars.

 

So, with a parallel four bar you want them to intersect on that imaginary line, so the bottom should be angled slightly up and the top angled slightly down? I had a couple of ideas in my head. This photo is the rear end bottomed out on my bump stops, so the LCA angle isn't what it would be at ride height but a couple ideas I had.





When I play with the calculator, I can get a higher anti squat percentage by dropping the angle of the bottom bar lower (at the rear axle) and increasing the height of the top bar at the axle. It doesn't seem to matter what the length is of the top bar.