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Touque Arm rear suspension

747mopar

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I'm beginning to accept that my car will never be done... Goon and I have been tossing around the idea of ditching our leaves in favor of a 4 or 3 link but after thinking about it we thought a torque arm might be a good option. To me this is about the most positive way of eliminating axle wind up with a tremendous amount of leverage and the fact that it would be easily applied to a B Body provided I can build an arm that fits along side the driveshaft is a huge plus. I've got some research to do before I start building them but here's some pics to better illustrate our goal plus a link.
http://http://www.pro-touring.com/threads/85354-Rainy-Day-suspension-basics-what-IS-the-deal-with-torque-arms

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I do like the idea!!
 
Great topic.
There is a ton of info out there on rear end setups for Street /Drag /Pro-Touring setups and you can easily get lost in the cloud of available options. But before you dig in and start welding . Remember. For the average guy with a strong street car the rear Leaf setup still holds a lot of tune-able credibility. Probably more than you'll ever need.
But as far as adding a new 3-4 link setup I like the simple route. simple cause at the end of the day I'm 99% street use.
The 3 link setup especially with the torque arm is nice . Its simple adjust ability and leaves little room for binding and less contact points to the chassis can help keep the street durability of the car. I'd still stick with a grommet or bushed style end link at all the body mounts just to keep the vibration under control.

Nice Stuff
Ron
 
That's my thoughts as far as the bushings go accept with a torque arm the end of the arm (near the tranny) needs to be able to telescope a small amount plus rotate as well. The 3rd gen Camaro's trapped the end of the arm in rubber where it could slide and twist a bit but I'll likely do something a bit beafier. Your right about leaves but I want to eliminate windup, side to side movement and add more ride height adjustability plus I just like screwing with stuff.
 
This is the GTX that Legendary Motor company built on the TV show. It was at the Detroit Autorama a couple weeks ago. It says they used a truck arm suspension, is that the same or similar as the torque arm type? Sorry my knowledge and skills aren't anywhere near most of the people on this site.


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Mike and I were having the same conversation. I like the idea because it's different. I built a triangulated 4 link with bushed rod ends because it was easier for me.

What at advantages do torque arm style 3 links have over a 4 link? Are you running a watts or panhard to locate?
 
I'm still researching but ease of fitment is one huge benefit since fitting a 4 link in a b body requires short upper arms or cutting and the other is less bind. I'm leaning towards the Panhard. The watts might be better for keeping the axle perfectly centered threw the travel but a b body lowered 2" only has a minimum amout of travel left meaning if the Panhard bar is set just below parallel and only travel 3"-4" up and down there's virtually no side movement threw the stroke. To me it's just wasted time and money on this particular application but I know very little haha.
 
Yes my uppers are short, my one buddy told me to put the kit for sale and call it T-Rex because it has long legs and short arms.

Are you thinking of using the leaf sliders for the front of the torque arm? When I was chatting with Goon (Mike) about it, I misunderstood and figured he was talking about a wishbone style 3 link.
 
Well we've talked about a few option so he might have been depending on how long ago it was. I am planning on bolting the lower links where the leafs do now.

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The shorter uppers will cause the pinion angle to change some threw the travel which is the downside to that but that's how all the companies make them for our cars.
 
A lot of conversation and changes since this conversation started Saturday morning. First idea was to mimic the XV engineering style. From there it's resulted in a lot if reading and discussion. So much good information out there
 
I think you have a good idea and I am intrigued. I never entertained a torque arm idea.

How much movement would the front link require? I am assuming the same as the slip yoke? Does your forward torque arm link break at the same point as your universal joint?
 
I had a 3rd gen Camaro years ago and it was located right beside the universal joint, I would guess your correct on the slip yoke since they are traveling the same path.
 
Im thinking the Truck arm suspension is good for High Speed stability. it's triangulated so I'm sure the rear axle stays put , although with that length of swing arm I'm sure a panhard bar would be benificial.
As for Pro-touring ..I can't see it being as effective. because the Truck Arms are fixed to the axle and the rear end would surely be giving the joint at the axle and the front of Bushing at the crossmember a good workout. Visualize the front arms are body mounted at angles. and the rears are mounted to a live axle. seems like a lot of loading going on there.

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AFCO once did a write-up on rear Leaf Spring setups...(I've got to hunt it down) but as I recall moving your forward spring mounts inward by 1" each side and leaving the rears in their original location effectively triangulated the rear leaf setup. and by carefully shimming your springs to prevent loading while tightening the U bolts you ended up with a pretty hood setup.
switching out the rear Leaf spring Shackles to sliders is also a great way to eliminate rear end swish.


Food for Thought
Ron
 
Just so everyone is clear we are not talking about the truck arm setup. I can definitely see what your saying about a rigid mount at the axle and all the movement being at the front. Probably fine for truck pulls but not anything that really cranks the axle.
 
nascar uses the truck arms with a panard bar .

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i had thought about the torque arm when i 1st got my charger, at the time i still had my 3rd gen camaro & it is a good set up.
 
Just so everyone is clear we are not talking about the truck arm setup. I can definitely see what your saying about a rigid mount at the axle and all the movement being at the front. Probably fine for truck pulls but not anything that really cranks the axle.

Sorry 747mopar, people probably got confused with my post. I was trying to find out if torque and truck arm setups were indeed different.
 
Sorry 747mopar, people probably got confused with my post. I was trying to find out if torque and truck arm setups were indeed different.

Truck Arms--The NASCAR Favorite

Chances are, the only time you have seen a truck-arm style (aka center drive) rear suspension is if you looked under a NASCAR racer. Winston Cup, Busch Grand National, Craftsman Truck, and IROC drivers have been tweaking this technology for the last 30 years. Hot Rods To Hell, in Burbank, California, has been retrofitting classic cars to center drive technology for over 10 years, so we hit them up for their insight on this system. HRTH had this to say, "To start with, a truck-arm suspension cannot bind under any type of condition. The suspension stays supple, the arms converge on an actual instant center and, because of their length, they remain neutral throughout bump, droop, and roll travel. The axle travels straight up and down so the wheelbase also remains constant. Your driveshaft slip yoke barley moves, and torque-induced chassis twist is eliminated. Also, the chassis is no longer being pushed around from the rear outer extremities by short little links, or the front half of leaf springs." HRTH also mentioned that the system eliminates wheel hop and is fully adjustable. These adjustments allow you to set the ride height and still maintain a level Panhard rod.


According to mechanical engineer Katz Tsubai, "The pros of a truck arm suspension are stable IC location, good roll steer characteristics, and good yaw response. This results in consistent behavior under both acceleration and braking. As for downsides, he points out the overall weight of the system, both sprung and unsprung, is quite high. Also, since the trailing links are rigidly mounted on the axle, components must elastically deflect in order for the suspension to roll. Try visualizing the whole suspension system as a giant anti-roll bar, with the axle assembly being the bar and trailing links being arms. You can see why the system restrains the roll." It should also be noted that running a full exhaust system with this type of rear suspension is quite a challenge due to how much real estate the components eat up under the car.



Torque Arm

A torque-arm suspension uses a long arm--rigidly mounted to the rear center section--that runs from the center of the differential to a point near the transmission to absorb rear axle torque reactions. The design specification of a torque-arm setup is similar to that of a three-link style suspension. The most important factor being that the lateral location of the rear end must be kept with a low roll center to avoid unpredictable suspension responses. In this type of suspension, a Panhard bar or Watt's link is required for keeping the rear end centered. Torque-arm suspensions have been used on cars for quite some time, all the way back to the 1930s. When designed properly, this style of suspension can offer good performance characteristics. The most notable performance cars to use this suspension are Camaros and Firebirds made from 1982 to 2002. They employ a torque arm along with trailing arms and a Panhard rod.

One other concept seen when discussing torque-arm rear suspensions is "decoupling." When a torque arm is directly connected to the chassis, the rear end can physically be lifted off the ground under hard deceleration. This is referred to as "brake hop" and is something you want to avoid. By decoupling the torque arm from the chassis, you avoid the braking torque being transferred through the torque arm. This is accomplished by only letting the torque arm contact the chassis under acceleration and by allowing the other links in the system to absorb the braking torque. In this way the acceleration and braking functions are separated and each can be optimized individually.

Getting a properly functioning torque-arm suspension is not an easy task. The length of the links and their placement has to be dead-on. Also, the bushings used, damping rates, spring rates, and preload must be calculated to work together in controlling all the forces.





When we asked mechanical engineer Katz Tsubai about what he felt were the pros and cons of torque-arm suspension he said, "One pro is that the system is kinematically free in roll. As with a three-link, the suspension is free to roll when Heim joints are used. As a result, tuning is much easier and the end result is predictable and won't surprise you by causing conditions like snap-oversteer." He also pointed out that it's possible to achieve good roll steer characteristics with a low roll center. Added benefits would be that the system is fairly simple to retrofit to an older car since you do not have to cut up the floor and trunk. Additionally, depending on the layout and centering device used, it's relatively easy to route a full exhaust system.

On the down side, Katz stated that he felt the system had a low anti-squat value, depending on how the trailing links were arranged and that it's difficult to get high anti-squat without causing roll oversteer or severe brake hop. This would be more of a problem in a short-wheelbase car that would use a relatively short torque arm. Kats also related that in some cases the system has limited adjustability. Since the length of the torque arm is fixed, any changes to adjust the anti-squat value will also change the roll steer characteristics. On the subject of decoupled torque-arm setups Katz added, "The idea is to free up the torque arm from reacting to braking torque by adding a telescoping auxiliary link. This allows you to have very high anti-squat value, while keeping brake hop, which is normally associated with high anti-squat, at bay. The system is very sensitive to tuning, particularly preloading."

In practice, we've not noticed degraded anti-squat or brake hop in either factory torque arms, or the Griggs GR-40 system for late-model Mustangs. Under hard track use, the most common torque-arm designs offer adequate, or even superior, anti-squat characteristics. It's important to note that the ill-handling traits regarding torque arms apply only to short torque arms, so if you plan on fabricating one yourself, make sure you've got the real estate necessary for an effective design.
 
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I'm beginning to accept that my car will never be done...

LMAO . . . That's my plan when I get my car done the first time . . . every Winter work on it to add something and make it better !
 
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
 
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