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Touque Arm rear suspension

Mr.SpeedFreak said:
You guys are nuts hahaha

So was the upper arm length a major deciding factor in traditional 3 link vs torque arm? I've been pretty settled on 3 linking both my cars but I'm stoked to see where this goes. Probably right on the watt's vs panhard deal, watt's would obviously be 100% perfectly centered throughout range of motion, but wouldn't think it'd be a huge difference with that much travel. Or you could just bedazzle us with building your own Watt's link so it's cheap AND perfect! Lol!

You guys might find this interesting, the guy's build is insane in general, and he did some ungodly decoupled TA setup

http://board.moparts.org/ubbthreads/ubbthreads.php/topics/1165278/7.html
Click to expand...


Just noticed the Signature at the bottom of the TT Cuda build is CJD Automotive... the same shop doing the "Not a body over" thread! I've pm'd him for input :)
 
That's cool, always great to get some tips from someone who's been there and he's definitely got skills.
 
I am by no means an expert on suspension design, but I use one to get proper geometry! So you wanna 3 link? I am a huge fan of a 3 bar setup (and a crazy decoupled 3 bar going in my 'Cuda). Just so we are on the same page, remember everything is a compromise. Torque arms work well, but have very limited tunability, so the geometry needs to be pretty close to start, which leads to compromise number 1. If your going for a bolt in, using the forward leaf perches as the mount for the trailing links may not be the ideal location or length. You'll need lateral axle location. A pan hard bar is more tunable than a Watt's link and requires much less space to package and mount. Mounting the torque arm to the axle and making a mount is something else that would need to be addressed. If your really serious, to start you need very accurate dimensions. Some of those would be, car at ride height, you'll need the height of the forward trailing arm mount at the bolt centerline and that same bolt centerline to the axle centerline, distance between the two forward mounts, etc...
 
Friend and I tried putting a torque arm on his 76 bronco with 39"'s. We were both suprised when the arm was easily broken, it was beefy too, forget the size of steel we used. He was having a big problem with axel wrap on lifted leaf springs. We swapped in a ford 4.6 mod motor and drive train last spring, getting the drive train angles to work was difficult. He ditched the leaf springs and went with a prefabbed 4 link setup. Fairly different application though.
 
CJD AUTO said:
I am by no means an expert on suspension design, but I use one to get proper geometry! So you wanna 3 link? I am a huge fan of a 3 bar setup (and a crazy decoupled 3 bar going in my 'Cuda). Just so we are on the same page, remember everything is a compromise. Torque arms work well, but have very limited tunability, so the geometry needs to be pretty close to start, which leads to compromise number 1. If your going for a bolt in, using the forward leaf perches as the mount for the trailing links may not be the ideal location or length. You'll need lateral axle location. A pan hard bar is more tunable than a Watt's link and requires much less space to package and mount. Mounting the torque arm to the axle and making a mount is something else that would need to be addressed. If your really serious, to start you need very accurate dimensions. Some of those would be, car at ride height, you'll need the height of the forward trailing arm mount at the bolt centerline and that same bolt centerline to the axle centerline, distance between the two forward mounts, etc...
Click to expand...

Thanks for chiming in, the purpose of this thread is to learn. I'm hoping to learn and hopefully get some good info on how to set it up, as of now I've had very little luck finding any good technical data on how to go about figuring up the geometry.

- - - Updated - - -

Any links or guidance as to where I can find more info would be much appreciated. I would rather have a really good idea to start with than spend a lot of time redesigning down the road so for now I'm just going to keep researching.
 
I agree Dev, I've been reading as well and it seems to get the design basics you really need to start by deconstructing a factory application that has been proven and understanding the geometry from there

One further thought I was discussing with Zach (Tzclark) and it's more important for you than me but that's ground clearance?
 
HYRDGOON said:
I agree Dev, I've been reading as well and it seems to get the design basics you really need to start by deconstructing a factory application that has been proven and understanding the geometry from there

One further thought I was discussing with Zach (Tzclark) and it's more important for you than me but that's ground clearance?
Click to expand...

I don't see ground clearance as an issue provided I can fit the arm beside the driveshaft which could be tougher than I'm thinking. I'll have to get the car on stands this weekend and just look it over. Go back to the pics on page 1 and look at the blue setup under the car on the rotisserie, that's what I'm thinking. Looks like it takes up very little room in the tunnel.

- - - Updated - - -

Mr.SpeedFreak said:
You guys are nuts hahaha

So was the upper arm length a major deciding factor in traditional 3 link vs torque arm? I've been pretty settled on 3 linking both my cars but I'm stoked to see where this goes. Probably right on the watt's vs panhard deal, watt's would obviously be 100% perfectly centered throughout range of motion, but wouldn't think it'd be a huge difference with that much travel. Or you could just bedazzle us with building your own Watt's link so it's cheap AND perfect! Lol!

You guys might find this interesting, the guy's build is insane in general, and he did some ungodly decoupled TA setup

http://board.moparts.org/ubbthreads/ubbthreads.php/topics/1165278/7.html
Click to expand...

To me it seams like all the kits sacrifice proper setup in order to make them a "bolt in" unit. The torque arm just seams like a better fit and from what I'm reading is a very good setup with lack of adjustability being it's biggest set back. This is why research is important, get it right and leave it alone.
 
Their is no way to go half way on this and have any hope of it working. Copying another vehicle is not going to be ideal. You need to contact Ron Sutton and he will outline the dimensions needed. He'll plug that info into the Performance Trends software and tell you what is the ideal setup. He can calculate your trailing arm angle, torque arm length, etc, to optimize the setup within the "bolt on" confines. Until you get hard numbers and actually map it out, it's just a guess. Ron normally charges a few hundred dollars or so to plug in the numbers and optimize the setup. Cannot reiterate this enough, accurate measurements are critical! If you decide to go that far, contact me and we'll see about building some kits.
 
Thanks, I was actually on his sight last night, I'll look into having him run the numbers. As far as building them goes I'll be doing that myself, no fun in paying someone to do it. Realize we are only in the beginning stages of this idea and have no intentions of half assing it or copying a setup off of a completely different car which is why we're asking questions. Appreciate the tip, I'll let you know what we come up with.
 
Good read.

The key for me is that you can't analyze a T/A the same way as a ladder bar, or any multi-link suspension with a known SVSA. If you think of the forces in the suspension not as "jacking" effects, but as torques which must be reacted by the suspension members, it makes this easier.

Example: car with 100" wheelbase, 20" C.G. Call the ratio of these two, 20/100 = .20, the weight transfer ratio (WTR). If we have a ladder bar with forward mount point 10" off the ground and 50" forward of the axle center, we can construct another ratio, call it the anti-squat force ratio (AFR). In this case, the AFR is 10/50 = .20, and the percentage anti-squat = AFR / WTR = .2 / .2 = 100 percent. Easy.

Torque arm is more problematic, because the effective lengths we need for the above ratios are no longer determined strictly by a physical (ladder bar) or virtual (multi-link intersection) center point. Here's the torque arm analysis, starting with trailing links that are level with the ground. Think of the force on the contact patch generating a torque by acting on a lever arm which is the height of the level trailing links. This torque is reacted by an essentially horizontal arm, the torque arm. Thus, the anti-squat force ratio (AFR) becomes the height of the level trailing link, divided by the length of the torque arm. Back to our above example, if the level trailing link is 10" high and the torque arm is 50" long, the AFR is .2 and our anti-squat is 100 percent again. Note that for nearly level torque arms - which is always the case - the height of the front torque arm mounting point is essentially irrelevant.

If the rear trailing links are angled up or down in the side view, the analysis is complicated somewhat because the trailing links will add their own "jacking effects". If the links are angled down toward the front, they will reduce anti-squat, if up, they increase it. This effect is also simple to calculate: divide the vertical gain in distance from rear to front pivot by the horizontal distance from rear to front pivot. For instance, front trailing arm pivot is 10" high, rear pivot is 11", horizontal distance between pivots 20", the anti-squat force ratio contributed by the trailing links is (10 - 11) / 20 = -.05. Angling the trailing links upward to the rear "stole" a fourth of our anti-squat in this case. So the formula for anti-squat is: (AFRtorquearm + AFRtrailinglinks) / WTR. AFRtrailinglinks is a positive number for links angled down to the rear, negative number for trailing links angled up to the rear.

What if we do want to make our trailing links angle upward to the rear, to induce a bit of roll understeer? Well, we can shorten the torque arm proportionally to recover the desired anti-squat - in the above example, we need to increase AFRtorquearm to .25, which we can do by shortening the T.A. to 40". Won't that shorter torque arm lead to more brake hop? Curiously, maybe not in this specific instance. Remember that the front of the torque arm is constrained only in the vertical direction, it is not a pivot point. The actual side view arc of motion (the SVSA) will be larger in radius than the torque arm, because the links angled up to the rear will "push" the axle backwards somewhat as the rear of the car lifts. Of course, once the trailing arms move past level, the opposite will occur, and the SVSA will be shorter than the T/A length.
 
Really cool to see CJD on here and the input he's adding, your work is incredible man!

You guys might also find this interesting as a sidenote, this guy put together his own standard 3 link with watt's link in his Falcon, came out pretty cool and there's a bit of discussion throughout the build thread on some basic rear suspension geometry and tuning. Main thread that got me going on my own research

http://www.pro-touring.com/threads/58842-Project-BLUEprint-1965-Falcon/page18
 
Resurrecting this thread with a question. Still leaning towards torque arm but 3 link hasn't been ruled out (or still even 4 link for that matter if it is the right choice)

With a Procharged 522 I stand to put down a good amount of HP and Torque. Would the TA be up to that? Obviously need a designated cross member for the forward connection point
 
HYRDGOON said:
Resurrecting this thread with a question. Still leaning towards torque arm but 3 link hasn't been ruled out (or still even 4 link for that matter if it is the right choice)

With a Procharged 522 I stand to put down a good amount of HP and Torque. Would the TA be up to that? Obviously need a designated cross member for the forward connection point
Click to expand...
My opinion is the torque arm if built correctly is the strongest because of the tremendous leverage of such a long arm. The leverage means it takes less to hold it in place at the end but also means it needs to be beefy on the other end and anchored well to the rearend. Since your having a custom rear built mounting the arm is easy for you.

I had an 80s Camaro with the factory torque arm, it was literally bolted to the tranny with a small rubber lined strap and a few small bolts.

I'm by no means an expert but leverage is leverage. Once I tidy up my garage the torque arm is going on the Charger:thumbsup:.
 
Torque arms work for many different power levels, just have to beef up the components. Look at what Speed Tech has or Grigg's Racing. TA's are a compromise for packaging and will never out perform a 3-link in acceleration and braking. Here is a pic of the 3-link setup in my 'Cuda:


 
That's definitely different but hard to install while maintaining a rear seat I assume? I'd love to see better pics, very nice work!
 
CJD Speedtech is EXACTLY the company I was modelling after seeing one of their complete chassis on a Pro Touring Divco Milk Truck project a friend is doing.

These look plenty stout to me!

Speedtech.jpg speedtech1.jpg speedtech2.jpg speedtech4.jpg speedtech5.jpg speedtech6.jpg
 
That looks pretty stout! Don't think you'll brake that arm but I'd love to see better pics of the mounting at the pinion. Looks to be a 9" Ford using the pinion carrier bolts as a mounting location?
 
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