My take on a "truck arm" suspension

Also called a 2 link. I used 3 inch I beam. I cut 4 plates, 2 to weld to the housing and 2 to weld to the I beam. I also wanted to mount the spring to the tails so they were pie cut to bring them in parallel with each other. The shocks will also mount to the beams.
One big advantage I see with this is the lower than usuall mounts for the shackels. Thus causing the crossmember to be low and not interfere with the backseat of my sedan.
Here's a couple pictures. Obviously, I have mucho welding and gusseting to do still.

 

And here is a pic of my K member with drop out trans mount.

And my new brakes, courtesy of Riley Automotive. Eric rules.

 

From the pictures, it appears you have created a M***IVE rear anti-sway bar!
The rear arms solidly attached to the axle will not allow the axle to move - one side moving up and down independent from the other - without placing a tremendous strain on the attachment points.

 

it would seem that way but this is pretty much how the GM factory truck arms are on 72 and earlier trucks... other than they used coil springs.

 

That's a neat idea with the spring, but I'm not sure it'll work very well. Looks like it'll bind up very easily, not to mention making the car handle badly. Hope it does work, though. I'm interested in hearing how it works for you.

 

kinda scares me . i would put some kinda pivot at where it mounts to the diff.

 

Damn, and I thought I built some beefy stuff. They are right about it not having much movement in the rear though.

 

Forgot to put this, you could possibly put johnny joints in it, and that would take care of any binding where the arms mount to the frame.

 

wow you really like heavy materials yeh..they certainly wont bend!!
the plate you used for the Kmember is ridiculously oversized in my opinion, but like i said, it wont bend either!

 

This gets discussed about once a month. As GM used this for their trucks for a number of years it's a proven system. You've gone beyond even their design with way heavier material. It will function fine as is but with a stiff ride I suspect. Your unsprung weight is quite high so that will contribute to a harsher ride but you're not going to break anything, thats for sure.
Tell us about your drivetrain plans (engine, trans) to see what the total package will look like. Also what body will go on this?

Frank

 

I've done this recently also. I used a set of arms from Hot Rods to Hell. They have a big bushing in the front to allow movement as did the GM ones. As long as the bushing (or heim joint) is used there is no need for any movment at the rear diff. Chevy c10 used it like this for 15+ yrs. Nascar guys have copied it and refined it. It'll ride just fine and handle great.

 

Id drill the **** outta the arms to lighten it up and it will look bad *** too..
Dave

 

Agreed!
Big rubber bushings as close together as possible,with lots of room to work is the key.

The crossmember is too thick to be using IMHO...especially in an unboxed frame. Weld connections are gonna be cold with all that meat to soak heat from the joint. I don't like being negative but I have to say I'd rethink it.
(Why don't people ask about stuff BEFORE they do it???)

Also...I know more bracing/gussets are intended...but you really should be grinding off the mill scale and Ving your joints before you weld. Makes the welding easier and the joints much stronger.

 

I just did a similar setup on my truck with a transverse spring. It rides great and doesn't bind at all. I checked it by moving the rear axle throughout it's range of motion with the rear spring out. The fact that the front mounting points are as close to the driveshaft as possible lets it articulate just fine, provided you use a big bushing. The pinion angle changes slightly, but definitely not as much as a parallel leaf setup under load or braking. I think Clark has done a tech piece on this and it has been discussed at length. Bottom line, if done correctly it works great. Now, your spring hangers, I'd be a little leary of... Looks like if you hit a big bump and the spring tries to flatten out, the shackles are going to bang into the ibeam...

 

Looks good and safe, those of you who are iffy, have you ever seen a rear axle of any modern FWD vehicle? Most have rigid rear axles and solid mounting arms, they just pivot on two bushings on the arms at the front, there is no side to side suspension.

 

I don't know if I'd make that comparison, this is his drive axle in a hot rod! Apples and oranges...

 

The rear axle on a modern car is designed to twist and flex so I don't believe that is a good comparision.

In my old roundy round cars I ran truck arms, both factory/converted chevy truck and custom ones out of 2x3 box. I've run monoballs, rubber bushings, and steel bushings up front and no matter which I still ended up putting a hunk of rubber between the rear end mounts and the truck arm itself, all held together with a U bolt. The more rubber, the faster we went believe it or not; I think because it allowed for a little axle wrap while under power, thus cushioning the shock to the tires.

Truck arm (rear end) mounts are cheap and easy to find & install, just check out Stock Car Products online, order a pair, weld them in and use a U Bolt and some rubber (1/2 to one inch thick) and the rest of your deal should be fine.

You can even purchase one of their truck arm crossmembers, which will have a slot and elipitcal bolt/washer on one side to square up your rear end.

This will save you a lot of fabbing and make for a clean, safe setup.

I personally would shorten the rear of your arms and mount the shackles off the back of them instead of the side.

I do like your general idea though, I had moved the springs to the rear (behind the axle) on my last truck arm car and it helped cornering a lot plus allowed me to run a softer spring.......

Al in CT

 

You'll be fine. The I beam allows twist.....and it will! I've done about a dozen cars with a suspension similar to what you have done. All worked great. If you would have used tubing you would have had problems.

I haven't used a transverse spring yet. Your set up is cool. The only thing I would change is your verticle plate could be angled to the center web at the bottom to allow more travel of the spring. I doubt it will ever get that far but better safe than sorry.
Clark

 

Wow, lots of opinions here. I wasn't posting this to ask if it would work okay. I know it will work great. As to the gauge of the materials, That 3" I beam really looks beefier than it is. The center crossmember is a little thick, but it was free material, and the frame is getting boxed around it. This is all going under a 30 A Tudor with a fairly heavy engine and trans, and I build my stuff to last.
The arms are mounted with a large bushing from energy suspension and it all swings and pivots very smooth.
As to the couple of guys who said it looks scary, ehh.. sorry. Go read a suspension design book or look under most circle track cars.

 

>>>and it all swings and pivots very smooth.>>>

Good, you should be fine then

Al in CT

 

Looks good to me!

 

Read your post on the truck arm style suspension and I am in agreement, that while appearing to be heavy, will not be a problem . What I have experienced, is that without a fixture, it is difficult to position the rear axle perfectly square using fixed front mounting points. You can improve the installation by providing an adjustment point at the front pickup as suggested by Al. This will give you the ability to re-square the suspension at ride height and compensate for elastic tape measure errors. Al's other suggestion, to use a compression shim in the rear also will also help dissipate the torsional stress p***ed on to the beam during articulation.

 

I think you're misunderstanding what I meant by binding up. The truck arm is a proven design and I have no issues with it, it's the way your spring is mounted that I'm concerned with. It just seems like it won't be able to give you the travel and handling that you can get out of this suspension.

 

I'm curious to what you see that will bind anymore than the "standard" set up with say Pete and Jakes ladder bars with a transverse spring. Maybe I'm missing something, or maybe my pictures are decieving. This and every other frame I've built will only have 4-6 total inches of travel anyways.

 

I admit, I'm not as familiar with transverse leaves as I am with other suspensions, it just seems that the individual arms won't be able to flex very well independently. I know it's been used successfully with other suspension designs, so maybe it'll be ok. Either way, I hope it does work great for you and that's definitely an original design.

 

That was the point that concerned me.
GM uses LARGE rubber bushings to allow a "torsional" flexing of the arms.
This occurs when one side - wheel - rises over a bump - and tries to rotate the axle along the longitudinal axis of the vehicle.

There doesn't appear to be any "flexibility" where the arms attach to the cross member.
So, when one side - wheel - rises; it tries to "lift" the other.
Which is the principal of an anti-sway (or roll) bar.

Sure it will work ... for a while, until some overstressed welds break.

 

I was taught that welding thick and thin metals together will create stress issues on the thinner areas once things start moving and flexing around, creating stress cracks... Ie, the thinner surrounding metals can flex and move around somewhat, and the thicker, stiffer metals will hold firm, creating cracks around the joints.
I understand u wanting to overbuild and use whats free, but sometimes I think overbuilding can create headaches of their own...

 

Thats why I-beams are good for this design. They have low resistance to torsion, so they will twist to allow the axle to move. If the arms were made of round or rectangle tube, there would be issues.

 

And like Digger Dave brought up, I did use big 2" O.d. urethane bushings. Thanks for all the comments. I just wanted to show how I did it.
Crusty

 

"...the individual arms won't be able to flex very well independently."
everybody's thinking like the arms are out of plane with the axle. The arms come close enough together that it's a wishbone suspension. no matter how the axle moves, the axle center, and both arms will always be in the same plane.
If the arms were parallel to each other making a U with the rear being attached to the fame rails instead of in the center and not a triangle...then the twisting y'all are envisioning WOULD be happening because as the rear end tilted it would force the arms into different planes of movement. The necessity for a panard bar shows that the triangulation of the arms is not to locate the rear sideways in cornering but to keep the arms in the same plane of rotation as the axle rotates around the driveshaft center in cornering.