Fabbed trailing arms - need advice

[BossHogg69]

Like the title says, I'm going to attempt making a set of trailiing arms for my truck. Does anyone see a problem with doing this from 2x3 .120" rectangular tubing? I'm not running bags, just want something with less twist than the stock arms. I plan to run a 15/16" rear sway bar from an IROC-Z that will be used with the fabbed arms. Thoughts?

[Wild83C10]

Someone made some adjustable trailing arms out of rectagular tubing. Do a quick search in this section it should pop up.

[vin63]

Just in case...http://67-72chevytrucks.com/vboard/s...+trailing+arms

[BossHogg69]

I saw that thread and it's very good. Nuke used 3/16" 2x3 and ballistic joints at the front of the TA. I don't want to use the swivel joints because I have no need for the articulation those joints offer. I'm building a Pro Touring truck and need the roll resistance that a solid mount offers. I also have an adjustable PorterBuilt TA crossmember, so that is what I'll use to adjust get the wheels centered in the wheelwell. I just wanted to know if .120" wall would be strong enough and still offer a little flexibility, but not as much as a stock arm. I actually have two rear sway bars, on is 7/8" and the other is 15/16", I was gonna try both and see which one worked better with the fabbed arms.

[WellBilt Kustoms]

I think using 2" X 3" .120 wall tubing will be fine. Thats what I would go with if I were building a pair.

Post up some pics when your done! Have fun!

[BossHogg69]

Believe me, I'll have all kinds of pics posted up when I get the chassis into a roller. It's been a slow process so far, but hopefully I can get motivated and fire my welder up soon!

[WellBilt Kustoms]

Originally Posted by BossHogg69

Believe me, I'll have all kinds of pics posted up when I get the chassis into a roller. It's been a slow process so far, but hopefully I can get motivated and fire my welder up soon!

Believe me...I know all about slow process! Its better to take your time and do it right, then to rush and mess up, or even worse regret rushing it and cutting corners.

Maybe this will motivate you. Here are a few pics of the trailing arms I built for a customers c10 here at my shop.

[SCOTI]

Originally Posted by BossHogg69

I saw that thread and it's very good. Nuke used 3/16" 2x3 and ballistic joints at the front of the TA. I don't want to use the swivel joints because I have no need for the articulation those joints offer. I'm building a Pro Touring truck and need the roll resistance that a solid mount offers. I also have an adjustable PorterBuilt TA crossmember, so that is what I'll use to adjust get the wheels centered in the wheelwell. I just wanted to know if .120" wall would be strong enough and still offer a little flexibility, but not as much as a stock arm. I actually have two rear sway bars, on is 7/8" and the other is 15/16", I was gonna try both and see which one worked better with the fabbed arms.

It would seem that eliminating the twist the OE 'beam' type arms have while using the same type of bushing @ the front will increase inherent binding issues. Suspension bind while pushing the limits of adhesion in a corner (what pro-touring is all about) could possibly result in an inconsistent grip which is not a good thing.

The reduction in flex from the tube construction is a good idea. But it would seem to work better w/the swivel type joint in front to allow articulation vs. bind.

Just another perspective....

[BossHogg69]

Wellbilt -those arms are WICKED!!! nice work!

As for the swivel joints, it just seems like they offer so much articulation that the trailing arm would never get a chance to work as it was designed to. I could be wrong, but he swivel joints seem to remove any 'anti-sway' properties that using a stiffer trailing arm would offer.

[lakeroadster]

Originally Posted by BossHogg69

As for the swivel joints, it just seems like they offer so much articulation that the trailing arm would never get a chance to work as it was designed to.

Looking at the rear suspension design from an Engineering perspective:

The trailing arms are primarily designed to handle only tension and compression resulting from accelleration and braking and to support the rear springs.

Tracking is controlled by the rear panhard (track) bar. You don't want the trailing arms to take much of these loads.

The stock trailing arms are basically fabricated I-beams. I-beams can twist and were used by GM to do just that. A boxed stock trailing arm or new ones made from tubing will be much more resistant to twisting that results from articulation. While the arms that are shown above by Wellbilt look awesome, their engineering advantages in resisting torsion aren't needed in this application and can actually produce problems. If you use a rigid mount at the frame to arm position with a non-stock trailing arm you will indeed likely end up with binding, as Scoti pointed out, or even worse frame mount or trailing arm cracking problems.

Worth noting however is the twisting of the track arms is severely reduced on a lowered truck, especially one with a rear stabilizer bar. This is because of the reduction of possible articulation (less possible rear axle movement). Therefore you may never see a problem with the stock style ridgid mount, especially if factory style rubber bushing are used and not a harder "poly" style bushing.

I would suggest use of a swivel type joint at the trailing arm to frame crossmember mount if the trailing arms are anything other than the stock non-boxed I-beam style construction. At a minimum use the rubber bushings if you are going this route and periodically check the arms and their mounts for cracking.

I hope this helps and is not interpreted as preaching. I merely want to help, I really don't have a dog in this hunt.

[BossHogg69]

Lakeroadster - you post didn't seen like preaching at all - I'm glad to get whatever information I can. It's just that the aftermarket arms offered by CPP (round tube construction) and ECE (rect. tube construction) both use a fixed mount, so that's what I was going to pattern my arms from. I don't know if it's worth noting, but I will be running a 6" drop rear spring and possibly a .5" spacer if the stance needs adjusting.

I still have my factory arms, if anything I guess I could just weld down the seam of the arms, and be done with it, if that is the best way to go. My plan with fabbing a set included welding on multi-hole tabs to use as an adjustable panhard mount so I could set the track bar at the perfect angle (I have the curved CPP 'deluxe' bar), which I guess I could still do with the stock arms and a piece of plate to weld the tabs to.

[lakeroadster]

Don't let me stiffle your creativity, sounds like you have some great ideas.

My comments are based on engineering theory. I run stock arms on my truck and replaced the old rubber bushings with new rubber bushings. I personally don't like the hard poly bushings as they make for a harsher ride.

I guess my point is whatever the modification is that is being planned think about the application. In this particular case if you are turning off a level surface up into an incline surface, where one tire will be higher than the other this will make the trailing arm want to twist. The axle end stays in line with the axle, the crossmember end always stays in line with the crossmember. If the arm can't twist then the loads go into the bushings and if the elastic limit of the bushings is surpased something has to bend... maybe the trailing arm, maybe the brackets. Based on the arms geometric cross sectional shape (I-beam, square tube, round tube) and what grade of steel is used this may or may not be a problem. As I stated above stronger isn't always better.

Take a look at ladder bars, they use heim joints that can twist.

Just depends on how many load cycles and how much binding there is... alot of factors to consider.

Anytime you build something on your own, or even buy something that's different from factory stock, be sure to inspect it before putting it on and then periodically check the parts and their accompanying supports. Better safe than sorry, as they say.