Trailer Building Indepent Arm Building - Official Guide

[dieselcruiserhead]

Trailer Building - Indepent Arm Building: Official Guide

I'd like to start a thread here on the portal for home trailer builders that is the official source of information for independent A-arm building. As we know there is somewhat of a 'steep learning curve' to there where I believe if you take some simple approaches you can avoid problems.

I spent a couple months building my arms and took nearly "best" every approach possible but at the end of the day if I had taken a few approaches that could have been pointed out to me by a collective community, much like many other technical modifications to cars or trucks or trailers, then I would have been miles ahead.

I'd like to have people link to their threads if they exist (or post picture) and post what they think is best or worst.

 

[dieselcruiserhead]

Here is the approach I took. It starts here at this post in my thread:
http://www.expeditionportal.com/forum/showthread.php?p=320138#post320138

I basically started with Jeep bushings (first mistake) that allow my arms to flex under load - even if they are poly bushings. These will be elimintated shortly. You can see I used laser aligners to get the position and length right on my arms. This worked excellently:

Second was assuming that my factory M416 frame was up to snuff for independent arm mounting. I will be removing the cross member they are attached to and adding a much beefier custom cross member. From there I am assuming I will have no further issues.

I have to pull the pic off my other computer but will post them in a sec...


Best,
Andre

 

[dieselcruiserhead]

Here is some of the damage that occurred from the thin factory frame and you can also see some of the bushing flex in the arms.

So my personal critiques are:

Use heim joints or some sort of metal on metal setup for your attachment point.

And two, make sure your frame is up to snuff. There is no way I see, personally, to use a M416 frame with independent arms.

Good luck,
Andre

 

[dieselcruiserhead]

Best resource for bolt on or weld on equipment for home builders:
http://www.adventuretrailers.com/homebuilder.html

Also inexpensive heim joints for building trailer arms:
http://www.ballisticfabrication.com/

(currently having a sale through the next 4 days).

 

[R_Lefebvre]

Would delrin make a better bushing? It's stiffer than poly, but still low friction. Also really easy to machine. I made delrin bushings for my track car a few years ago and have been very pleased with them, other than they transmit lots of noise.

 

[emohn]

Another option might be to look into Johnny Joints. They're basically a rubber isolated heim joint - used commonly in custom long arm suspension kits. Of course, one of the key benefits of Johnny Joints is that they transmit less noise than metal-on-metal heim joints, but the other benefit would be longer service life than heims, which can get sloppy over time.

http://www.currieenterprises.com/cestore/categories.aspx?id=1232

Of course, I think that Johnny Joints and heims are both overkill for this application and like Rob's suggestion of Delrin bushings better. A Delrin bushing with a properly sized inner sleeve and bolt should be more than up to the task. One thing to note, though, is that the pivot point of the diagonal arm should be exactly aligned to the angle of the arm, otherwise you'll end up with binding, rather than pure rotation. Delrin + zerk grease fittings would be my way to go.

On the M416 frame, I would think it would be fairly trivial to weld in some plate to box off that portion of the cross member and perhaps add a pad to spread out the load.

-Erik

 

[dieselcruiserhead]

My thoughts are even delrin would provide too much flex. In this application particularly with a tire and tire wear at play that as close to no sideways flex is crucial. I think a brass impregnated copper bushing might be a good app or maybe a Johnny Joint as emohn suggested.

I have been looking extensively at heims and johnnies to keep the independent arms, or I'm considering adapting a solid axle design similar to 60LCConvert's approach. There is a great old CAD picture of the solid axle with airbags that is deep in this section but the picture is missing along with a lot of the old attached pictures from a server/database error. This is a big loss to this section and thread unless the original poster can re-post it (I can't even figure out who the OP is).

 

[emohn]

Delrin will *not* flex to any significant amount. It will deform or fracture if grossly overloaded, but not flex - at least not measurably so. Delrin is a plastic, not a rubber.

 

[James86004]

Here is some of the damage that occurred from the thin factory frame and you can also see some of the bushing flex in the arms.

Good luck,
Andre

Seems to me if the arm had a wider base, there would be less stress on the mounting points, which would help both the frame bending and the bushing flex problems. The tradeoffs are you will get more unsprung weight, and a little less ground clearance. Those tradeoffs still may be favorable compared to a solid axle.

 

[dieselcruiserhead]

Delrin will *not* flex to any significant amount. It will deform or fracture if grossly overloaded, but not flex - at least not measurably so. Delrin is a plastic, not a rubber.

Yes I know, I consider it similar to plastic cutting board material. I think it will still flex measurably to the point where I probably wouldn't use it though I may be wrong. Assuming there is a bushing for a CJ available it certainly could be an easy fix for me, personally..

 

[spencyg]

Oil impregenated bronze bearing material is great in a smooth running machine, but for shock loading it deforms readily. You would have a very sloppy suspension on your hands very quickly. I think a combination of delrin and spreading your arm mounts out (thus reducing the moment forces applied to the bushings) would make everything peachy keen. Another point is that your airbag looks to be bulging on the back side due to the mounting plate alignment. It seems that ensuring the mounting plates are parallel and in-line when the trailer is statically loaded would help a bit in that department. I know airbags are tough and would last forever in this application, but since we're "building the perfect independant trailer suspension", I figured it was worth noting.

All these pics are going to put bad ideas in my head for that support trailer I've been dreaming about for Boomer...

Geesh!

Spence

 

[emohn]

Yes I know, I consider it similar to plastic cutting board material. I think it will still flex measurably to the point where I probably wouldn't use it though I may be wrong. Assuming there is a bushing for a CJ available it certainly could be an easy fix for me, personally..

It's used in racecar applications extensively under high loads as a-arm bushings and in 3 and 4 links with more weight than you're liable to see on a trailer - specifically because it doesn't flex. It's doubtful, however, that there will be an off-the-shelf option specifically for a CJ, but delring rod is cheap enough to purchase by the foot and machine on a lathe if you have the access/ability.

 

[R_Lefebvre]

Yes I know, I consider it similar to plastic cutting board material. I think it will still flex measurably to the point where I probably wouldn't use it though I may be wrong. Assuming there is a bushing for a CJ available it certainly could be an easy fix for me, personally..

It's even stiffer than cutting board material. It's HARD. Probably stiffness similar to aluminum. I could easily make some up for you if you paid for the material and shipping, but I'd imagine shipping from Canada would result in a total cost, you'd be better off having somebody down there make it for you. But the offer is there. I have used it a fair amount, I had a little side business making a delrin suspension spacer (basically a big washer) for the Ford Focus, have sold something approaching 300 sets. It's super easy to machine, cuts about as fast as you can turn the handles.

I definitely wouldn't suggest it be used in 4 or 3 link suspensions. Those are overconstrained and rely on bushing deflection to move. If you make the bushings too stiff, they lock up. That's why I used Delrin on the front A-arms and steering rack bushings, and polyurethane on the back of my Focus since it's got a crazy overcontrained whacky-trailing-arm-SLA hybrid suspension. But I digress...

 

[dieselcruiserhead]

Very neat Rob. I have access to machining here so it wouldn't be hard to do. The question is how necessary is the "flex" and independent suspension on a trailer. I do love how the trailer currently handles, it follows me now anywhere and at any speed. But the question is if I really would lose a lot with a radius arm or 3 link. In regards to flex I also wonder how necessary that would be with a trailer as well - I'm mostly interested in suspension compliance. I do love showing people the independent suspension though and particularly its insane clearance

 

[MotoDave]

My concern with Heim joints would be maintenance, you might end up having to replace them every few years, and joints that big arent cheap.

Do you know what Durometer those bushings are?

I have used Energy Suspension bushings in a few places on the suspension on my my WRX, and have been surprised how hard they are compared to most Polyurethane bushings. You might give them a try, if they are available for your size: www.energysuspension.com

I have a few round chunks of Delrin at home I'd be willing to send your way, if you want to try it out. Send me a PM if you're interested.