Radius Arm Flip

[adventr]

I'm thinking about a radius arm flip for my 80. I have the required clearance (8" of lift on my rig), and would like to retain the driving characteristics that radius arms provide.

While a 3-link could be a viable option, it's just not for this rig. Radius arms work well enough for my use, and flipping them will get the front end geometry back to near stock.

So, who here has done a radius arm flip? I've seen other threads, but none had any useful pics. I've heard this option is popular in Australia, but my searching hasn't yielded any results.


Any interference issues? Looks like the panhard bar might be in the way where it attaches to the axle.

Spill the beans!

 

[Ebag333]

So, who here has done a radius arm flip? I've seen other threads, but none had any useful pics. I've heard this option is popular in Australia, but my searching hasn't yielded any results.

Any interference issues? Looks like the panhard bar might be in the way where it attaches to the axle.

No one in the States has done it, AFAIK.

You might need a RHD/high steer setup to make it work.

 

[lt1fire]

What does the flip help you do exactly.... browsed through other threads on it but never really understood what it did.

 

[adventr]

What does the flip help you do exactly.... browsed through other threads on it but never really understood what it did.

Relocates the radius arms to the top of the axle, which will allow them to be level with the ground, as opposed to the steep angle that they're currently at due to the lift height.

Will also correct caster to stock settings.



I'm not sure that flipping the arms would require you to relocate the tie rod. Looks like there would be enough clearance...

 

[adventr]

Ok, I'm doing the flip this weekend. I'll keep this thread updated with my results.


Front pinion angle on a stock 80 is 7 degrees.
My front pinion angle is 19.5 degrees.

If 7 degree pinion angle = -3 to -4 degrees of caster,
Then my caster is ~ +8 degrees.


I'm going to position the axle at an 8 degree pinion angle before I weld the radius arm brackets into the new position on top of the axle. This should put my caster right where I want it.
I don't quite want a full -3 to -4 degrees of caster, as I prefer a lighter steering feel when at low speeds.
I would be happy with -1 degree, and hopefully that's where I'll end up.

 

[kidglove13]

I did a bunch of reading over on Outer Limits 4x4 about it.
I did read that someone used their castor plates for the new brackets on top of the axle and it worked well for them
The only clearance issue I see is the panhard axle side mount looks like it would hit or be really tight.
I am subscribed
Interested to see how this turns out

 

[Walking Eagle]

Relocates the radius arms to the top of the axle, which will allow them to be level with the ground, as opposed to the steep angle that they're currently at due to the lift height.

The effective arm is still from the pivot point through the center of the axle, so you're not getting away from any issues with the geometry itself.

You will push your front axle forward a bit which will change that angle minimally.

You will get less for and aft movement in the bushings, which should free up a little flex.

You will get a big gain in ground clearance.

At 8", if you make the castor correct, won't you have driveline vibe issues? I mean, unless you cut and turn.

 

[adventr]

I did a bunch of reading over on Outer Limits 4x4 about it.
I did read that someone used their castor plates for the new brackets on top of the axle and it worked well for them
The only clearance issue I see is the panhard axle side mount looks like it would hit or be really tight.
I am subscribed
Interested to see how this turns out

Just read through that thread, actually.

Seems they have the same general opinion as I do. Flipping the mounts will:

Correct caster on lifted rigs (6"+)
Relocate axle to center of wheel well
Allow radius arm to be level at ride height (suspension works more efficiently)
Gain more clearance under axle
Allow for more clearance between radius arms and tie rod


Possible downside, is that it may (or may not) require modification to the panhard bar. Either way, that's not going to be much of an issue if you're already into it that deep.


I'm going to take some measurements tonight, and doublecheck all of my angles.

 

[adventr]

At 8", if you make the castor correct, won't you have driveline vibe issues? I mean, unless you cut and turn.

It's hard to tell with driveline vibes. I honestly don't know what's going to happen there. I do know that I'll be rotating the pinion down ~10.5 degrees from where it is right now.
The pinion is currently pointing well above the t-case output.

A DC driveshaft in the front should help if there are any vibes. Beyond that, a part time kit will be my solution.

 

[Ebag333]

The effective arm is still from the pivot point through the center of the axle, so you're not getting away from any issues with the geometry itself.

If this were true than the MAF drop bracket would be meaningless. It does the same thing, just on the frame side instead of the axle side.

You're changing the angle of the arm, so by definition geometry is changing.

 

[bhmmapping]

If this were true than the MAF drop bracket would be meaningless. It does the same thing, just on the frame side instead of the axle side.

You're changing the angle of the arm, so by definition geometry is changing.

the drop bracket changes one of the pivot points, the arm flip doesn't. I am interested to see how this goes though. my axle is shifted about an inch backwards with the caster plates I am running now and I have to do something to move it forward. IMO welding on new brackets on the top of the axle wouldn't be that much harder than redrilling and plating the frame side mounts and you gain the ground clearance under the axle.

 

[Walking Eagle]

If this were true than the MAF drop bracket would be meaningless. It does the same thing, just on the frame side instead of the axle side.

You're changing the angle of the arm, so by definition geometry is changing.

Nope, The path the axle moves is determined by the pivot point (where the arm attaches to the frame) and the location of the axle. If the pivot point doesn't move, and the axle location relative to it doesn't move, it does not matter if the arm is on the top, bottom, or middle. It doesn't matter if it's S shaped, L shaped or straight.

The only way you'll actually change the motion of the axle for a given height is to A) move the pivot point (Drop brackets) B) Change the distance from the axle to the pivot (Longer arms).

Because you move the axle forward a little bit when you do the flip, you get a little of B). If the axle was in the same location after the flip it would still travel the same path.

 

[adventr]

I just double checked my pinion angle, and its right around 19 degrees. It looks like I'll have to modify the routing of the brake lines that are attached to the axle, as they run along it's top side.
That shouldn't be too big of a deal.

It looks as though the brackets (when relocated to the top side) will just clear the diff lock actuator shield, and will clear the coil perches as well. I think the only issue will be right where the panhard attaches to the axle. May have to get creative there, or grind off the end (or "nose) of the passenger side radius arm.

 

[Ebag333]

Nope, The path the axle moves is determined by the pivot point (where the arm attaches to the frame) and the location of the axle.

Actually the path the axle moves is determined by the location of the axle side mounts.

We know this to be true, else you couldn't shift the axle forward/back by changing the bushings or installing caster correction plates (or doing the washer mod).

Here's an overly simplistic example.

On the left, a stock axle (or rough analog to it). In the middle, the flipped arms. On the right, a drop bracket.

The vertical and horizontal lines are just there to show distance and give a better idea for angles. The dashed line is also there just to show distance (so I could measure and ensure that I got the flipped arms and drop bracket adjusted by the same amount).

The circle describes the path the axle mount would take should it travel a full circle around the pivot point. There are two circles in the last one to show the original path and the altered path.

The axle didn't move in any of the three, to give a better idea of the difference that the axle vs the mount makes. Obviously in both flipping the arms and with the drop bracket, it would get pushed forward.

The arm stayed the same length the whole time, the only thing that changed was the positioning and angle. With both the drop bracket, and the flipped arms, the path the mount (and by association, the axle) will travel is essentially the same. Why? Well, because the arm is the same length and angle, so the pesky laws of physics dictates that it must follow the same path.

Because you move the axle forward a little bit when you do the flip, you get a little of B). If the axle was in the same location after the flip it would still travel the same path.

That's kinda the point. It's not in the same location.

 

[Brunt Force Trauma]

Take lots of pics when you do this. I may be following suite.

 

[adventr]

Take lots of pics when you do this. I may be following suite.

Will do.

 

[Walking Eagle]

The axle mounts will draw a circle around the frame mount. The axle center will draw a circle around the frame mounts. Does not matter if arm is on top or on bottom. The only diffference is the slight shift forward of the axle (away from the pivot) if you build the mounting brackets in such a way that it does that. The shape or location of the mounting of the arm (other than if it changes it's possition relative to the mount) does not change the path.

Even if you do move it an inch or so forward, it's not going to change the effective angle (straight light from center of pivot to center of axle) much. Not enough to counteract any of the issues with radius arms being at steep angles anyway.

Still get all the other cool advantages of a flip though - and looking forward to seeing it.

Couple dwg's from a way back thread.... It was a long and painful thread, in the end, everyone agreed except Sumotoy

 

[kidglove13]

Take lots of pics when you do this. I may be following suite.

X2
Someone attempting something alittle different
I like it

 

[kidglove13]

You might not be changing the actual path of the axle
But you are changing where in that path the arm is traveling
Under the axle it is at an extreme angle, on top it is more parallel to the ground and is at a different point in the arc of travel therefore will handle a little different i would think
Even though a radius arm is a radius arm
This can be done and make reversible if need be

 

[Ebag333]

Under the axle it is at an extreme angle, on top it is more parallel to the ground and is at a different point in the arc of travel therefore will handle a little different i would think
Even though a radius arm is a radius arm

Radius arms like to be flat. I've read several accounts of Aussie folks relocating their lower rear control arm mounts on top of the axle and finding it gave better handling/control/ride.

This is pretty much true for any link/arm (such as the panhard and drag link).