Extending stock radius arms vs new cage arms

[Hal9000]

Not the slightest idea, but I bet that the guys at Pirate 4x4 do.

 

[DanWheeler]

wow, that could be a really good idea. DO you know where you could get threaded inserts and rods for 2x2 square tubing?

wait a sec... no that wont work. yesterday I used some pens at work to model the radius arms and found that the radius arm actually needs to rotate perpendicular to the axle. The C bushings allow it to do that.

thanks for the idea though. I'm going to keep thinking about it.

 

[DanWheeler]

to clarify, the C bushings would normally allow perpendicular flex with the axles but a bushing between the sideplates would absorb that flex more easily than the C-bushings causing the 2x2 square tube to stretch the side plates out.

 

[Hal9000]

Sooo, No bushing... Just add a metal sleeve, or maybe even a pair of tapered bearings (if you want to get really fancy that is).

The more I think about it, the more I think that leverage between the plates is going to be a problem no matter what you do. I suppose that you could box in the bottom, but you'll need to be sure you can get to your caster adjuster still. You could also add a strap across the top on either side of each of the shock mounts and box the plates in completely. That shouldn't interfere with the articulation if you do it right.

 

[chuck]

to clarify, the C bushings would normally allow perpendicular flex with the axles but a bushing between the sideplates would absorb that flex more easily than the C-bushings causing the 2x2 square tube to stretch the side plates out.

If you use the rear heim the 2x2 tube will twist so will not cause any twisting flex on the side plates.

 

[Hal9000]

I think that what he's worried about is side to side leverage as much as twisting. Basically as the axle articulates, it will move in an arc and the alignment of the radius arm will not remain 100% straight. With the front pivot between the plates, he's worried that side pressure of the arms on the plate due to misalignment will tweak the plates. (correct me if I'm wrong here!)

I'm not 100% sure, but I think that having a heim at the frame end will allow the arm to follow the axle and eliminate this problem. The only possible issue would be bind/jamming due to triangulation between the axle and both radius arms, and maybe the track bar....

 

[DanWheeler]

I think that what he's worried about is side to side leverage as much as twisting. Basically as the axle articulates, it will move in an arc and the alignment of the radius arm will not remain 100% straight. With the front pivot between the plates, he's worried that side pressure of the arms on the plate due to misalignment will tweak the plates. (correct me if I'm wrong here!)

I'm not 100% sure, but I think that having a heim at the frame end will allow the arm to follow the axle and eliminate this problem. The only possible issue would be bind/jamming due to triangulation between the axle and both radius arms, and maybe the track bar....

imagine if the axle were articulated to 90 degrees. Although impossible, the radius arm would have to flex to 45 degrees perpendicular to the axle and 45 degrees on the rotation axis of the axle to still be able to be connected to the frame. So if you articulate the axle 45 degrees or even 30 there would still be a certain amount of perpendicular flex necessary for the radius arms to still be connected to the frame mounts.

For this reason, i wouldn't feel comfortable having any amount of the 2x2 tubing still in contact with the side plates.

That said, the typical home-made wristed radius arm design (using the stock radius arms) leaves a lot to be desired. All that rotational flex that would normally be taken up by the C-bushings is being taken up by the joint which is only designed to rotate on one axis.

 

[DanWheeler]

I thought of an idea for attaching a heim to the stock radius arm mounts but I'm not sure if it would be strong enough or safe. Again, i know this seems like a lot of trouble but I really want to retain the ability to go back to stock without a lot of cutting and grinding.

they say a picture is worth a thousand words but this picture might just cause a lot of questions but hopefully it makes sense. It is basically a U shaped bracket that would bolt into the stock radius arm mount to allow a heim to be attached to the stock radius arm mount

think it would work?

 

[Hal9000]

imagine if the axle were articulated to 90 degrees. Although impossible, the radius arm would have to flex to 45 degrees perpendicular to the axle and 45 degrees on the rotation axis of the axle to still be able to be connected to the frame. So if you articulate the axle 45 degrees or even 30 there would still be a certain amount of perpendicular flex necessary for the radius arms to still be connected to the frame mounts.

That's Basically what I said. I think that as long as you have a rigid pivot point at the front (Welded sleeve, or maybe bearings of some type instead of a bushing) that the C bushings at the front and heim at the rear should still do their jobs, but there's no way to get around some side loading That's just one of those facts of life as I see it. You just need to make the pivot point and side plates strong enough that they'll transfer the load to the C bushing. If you box the plates in then having some of the square tube bearing on the plates behind the pivot will actually help take the load off the pivot itself and transfer it to the C bushing. It'll basically become a sliding/bearing surface.

 

[Hal9000]

Wait, don't you already have the BC arms?

Either way, I think that if you want to keep the stock mounts, just do what BC did and mount the Heim through the mount as if it were the end of the radius arm, then make a saddle on the radius arm to attach to the heim. If you're fabbing new arms, that would keep the modifications to the stock mounts to an absolute minimum. The BC system welds a plate onto the stock mount, but as long as you don't weld it all the way around, it'll be easy enough to cut the welds if you decide to go back to stock. Or you could just drill a hole or two and pin (or bolt) the plates in place once they're tightened down.

The problems I can see with bolting a saddle to the existing mount is that the saddle itself will have to be very strong since it can't easily be gusseted to the frame. Also, with a single mounting point, it will be inclined to rotate. Also, keep in mind that it's going to act like a lever and could apply torque and side loads to the face of the mount which the mount wouldn't normally see. This is especially true if the heim ever gets bound up. Maybe the mount could take it but it's beyond me to figure out if it can or not.