Radius arm basics?

[The_Lobbster]

I need schooled on radius arm stuff. I want to build a radius arm setup for my samurai. Will not be doing any crazy wheeling, I’m more after a really smooth street ride, and just something different, since most samurai guys just run leafs. I’ve seen some pretty basic builds online, but some crazy hood fab here, so figured I’d ask my noob questions here.

I bought 6 joints, 1 1/4” shank, 4 poly bushing, and two Johnny joint type.

I was thinking of running a dual wristed setup, with one of the uppers having a removable pin for wheeling, inserted for street driving.

Tentatively planned on homemade axle brackets, coil pads and buckets, QA1 coils, with roughly 32” eye to eye lowers.

Current question, with a coil setup such as this, would I want my upper and lower coil buckets to be exactly “in-line”, or right above and below each other? Or would I want some sort of slight offset to account for the arc of the axle as it rotates upwards?

And what thickness of steel would I need for the axle and frame brackets? I would think 3/16” would be enough, maybe even slightly overkill?

many more questions to come, I’m sure. Thanks.

 

[N-Smooth]

@I Lean has some cool coil buckets with integrated mounts that he can make for you.

 

[I Lean]

Poly bushings and radius arms aren't the best combination, since the poly is pretty "hard" compared to rubber, and doesn't like to deflect. So you'll end up with restricted articulation, or blown out poly bushings, or some combination of those.

Your pinned "wristed" setup would alleviate the bind, but will wallow out the pinned hole pretty quickly on the road. Which also means noise as the pin clunks back and forth in the newly-slotted hole--and nobody likes noises.

For your spring bucket alignment, I'd shoot for having the spring sit straight at ride height. The arc when you compress and droop from there is easily absorbed by the spring anyway.

3/16" is probably plenty for brackets. That's why I usually go 1/4".

 

[Herzog]

I agree with Carl. Go with rubber at the axle side of the radius arms.

I ran a home made version of the RE radius arms back in the day on my XJ. It flexed plenty, I never felt the need to remove one of the uppers for any reason. It also felt pretty stable, I enjoyed that ride quite a bit.

The lowers on it were the large clevite rubber bushing and the uppers were the smaller upper control arm style clevite bushings and it worked really well.

 

[spaggyroe]

15-20 years back, I ran a wristed radius arm on my last early Bronco. It allowed for a lot of articulation off road, but was almost uncomfortably soft on road. On a current build, I would personally go with longer radius arms, or with a 3-link / panhard bar setup. Both might be hard to package in a sammy.

 

[The_Lobbster]

I found a thread on BC4X4, this guy used like 31" arms, which seem pretty long to me, but I would imagine it would help with pinion angle quite a bit. He used TG Trailcreeper joints for all 6 pivots though. A 3 link would be better, but there is hardly any room already, especially if I use a TDI again, as the oil pan sits so dang low.

I have the 4 forged, poly bushing ends. I wonder if I can just swap the poly for some rubber bushings the same size?

 

[The_Lobbster]

I should add I want to run a sway bar, similar to a Currie antirock, but something more homemade and cheaper.

 

[I Lean]

I should add I want to run a sway bar, similar to a Currie antirock, but something more homemade and cheaper.

Sway bar is not usually a bad idea--but may or may not be as necessary with a radius arm setup. On my TJ (which had radius arms), I enjoyed the sway bar. On my SAS Land Cruiser, I don't feel the need for one. And that's even though I have the parts on the shelf to build it.

 

[The_Lobbster]

I just want a sway bar because legally you're supposed to have one.

 

[The_Lobbster]

Thoughts on a single wristed setup? Eliminates the need to run a second wrist with a pin. I understand that the in the same manner as a double wrist with a pin, I'll probably have more sway. If I did this, I'm assuming I'd want both lower arms to be on the same geometric lines, if that makes sense, on the axle side? Looking at some other single wristed arm setups, it almost appears that the side with the single lower, the axle side mount is closer to centered on the axle tube, while the side with the wrist, the lower, mounts, well, lower than the centerline of the axle tube.

 

[Ashcat]

I just want a sway bar because legally you're supposed to have one.

You’re kidding, right?

 

[The_Lobbster]

You’re kidding, right?

That's not the only reason actually. I want it to be stable on road, but also because it's legally required. Also from my understanding, a swaybar set up properly, can assist quite a bit while wheeling.

 

[spaggyroe]

If you want it to be stable on the road, I personally would look at options that aren't a wristed arm. Having ran one myself in the past, I wouldn't say that it helped my on road stability at all.

You noted that you won't be doing any crazy wheeling. In that case, I wouldn't see the need to sacrifice the drivability to gain the articulation that a wristed arm would give you.

I would vote for a more conventional / traditional radius arm setup, or build something like the R.E. arms that @Herzog mentioned, or to lay out a 3-link. To me, all would be better options than a wristed radius arm.

Just my $.02. Good luck with the project.

 

[The_Lobbster]

I'm assuming R.E. is Rubicon Express? I'm trying to find pictures of their arms to give me an idea. Are they the ones that the upper link turns in towards the middle of the axle instead of directly above the bottom mount?

 

[Mouse]

That's not the only reason actually. I want it to be stable on road, but also because it's legally required. Also from my understanding, a swaybar set up properly, can assist quite a bit while wheeling.

Exactly what are you referring to that is requiring the sway bar?

 

[N-Smooth]

Radius arms will be plenty stable on the road and provide lots of flex off-road without a sway bar. The great majority of TJ and XJ long arm kits use radius arms. I personally don't see the point of wristing it when you say you're not planning on hardcore rock crawling. If you were I'd say look into a 3 link instead. My 2 cents

Edit: I'm going to supplement this even more- a standard radius arm setup will give you more flex than you can even use, guaranteed. Wristing is an old school deal that I thought had died out but maybe Samurai guys are dragging it back up again...?

 

[The_Lobbster]

Exactly what are you referring to that is requiring the sway bar?

State law states, saying that any vehicle with a swaybar, must have it in place. If not, it technically does not meet state safety inspections.

 

[skippy]

If you want stability, Keep your leaf springs

 

[skippy]

State law states, saying that any vehicle with a swaybar, must have it in place. If not, it technically does not meet state safety inspections.

Also no body cares about Johnny law

 

[The_Lobbster]

Radius arms will be plenty stable on the road and provide lots of flex off-road without a sway bar. The great majority of TJ and XJ long arm kits use radius arms. I personally don't see the point of wristing it when you say you're not planning on hardcore rock crawling. If you were I'd say look into a 3 link instead. My 2 cents

Edit: I'm going to supplement this even more- a standard radius arm setup will give you more flex than you can even use, guaranteed. Wristing is an old school deal that I thought had died out but maybe Samurai guys are dragging it back up again...?

A 3 link would be ideal, but with the room I have under it, it would be way tight. If I'm not wristing it, what is the technical name for a non wristed setup? Would that be considered just an arm with the whole thing being solid except for the joints themselves at each end?