Y-link / radius arm - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 9 Old 12-28-2009, 12:50 PM Thread Starter
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Y-link / radius arm

With the JK's articulation potential, there's a lot of discussion about eliminating binding in the 4-link setup, the reasoning being that no matter how high a joint can misalign, there will eventually be binding due to physical design limitations. Hence designs like the RK 3-link, which eliminates this binding potential.

I have an XJ also, and in the TJ/XJ world there are a lot of successful systems using a Y-link or radius arm setup. Cutting your control arm mounting points down to 2 obviously eliminates potential for binding as well, and you are then limited only by joint misalignment capability (barring some other physical limitation). Seems like sound reasoning.

Why then does no one offer Y-link or radius arm setups for the JK (other than RE)? Is there something about the design of the JK - weight, maybe - that makes this design less desirable than a 3 or 4 link setup? Would it be too stressful to the CA mounts with such a heavy vehicle? Just trying to figure out why no one has really adopted this design yet....it's so simple and seems like it would be effective.
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post #2 of 9 Old 12-28-2009, 03:52 PM
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A radius arm (Y-link) is an inherently binding design. During articulation, the two radius arms are trying to twist the entire axle housing, so the bushings at the axle side deflecting are what allow the motion. If you had solid mounting points at the axle (heim joints, for example) there won't be any articulation, just straight up and down movement. Separate the arms into 4, and you reduce the natural binding a LOT. Remove one of the 4, and you eliminate the binding completely.


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post #3 of 9 Old 12-28-2009, 04:13 PM
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Quote:
Originally Posted by TeraFlex View Post
A radius arm (Y-link) is an inherently binding design. During articulation, the two radius arms are trying to twist the entire axle housing, so the bushings at the axle side deflecting are what allow the motion. If you had solid mounting points at the axle (heim joints, for example) there won't be any articulation, just straight up and down movement. Separate the arms into 4, and you reduce the natural binding a LOT. Remove one of the 4, and you eliminate the binding completely.
That AND the stupid amounts of squat/anti-squat you get with them as well.

The only way to get rid of the bind is a "wristed" radius arm and even then you still have it.
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post #4 of 9 Old 12-28-2009, 04:29 PM
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Everyone's points here are great! Also, do not forget that you loose all of your instant center properties with a radius are design! They have their place in the world because of their simplicity, but there are better methods out there!

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post #5 of 9 Old 12-28-2009, 05:53 PM
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Quote:
Originally Posted by TeraFlex View Post
A radius arm (Y-link) is an inherently binding design. During articulation, the two radius arms are trying to twist the entire axle housing, so the bushings at the axle side deflecting are what allow the motion. If you had solid mounting points at the axle (heim joints, for example) there won't be any articulation, just straight up and down movement. Separate the arms into 4, and you reduce the natural binding a LOT. Remove one of the 4, and you eliminate the binding completely.
x2 but add a little. If you go that way you have two options to eliminate binding;

1. Wrist one of the arms. eg. remove one of the y legs.
2. Wrist the whole housing. eg. cut the housing and allow the arms to run independently.

If you want to research radius arm set ups search the Early Bronco sites. They have been dealing with them since 1966, the first coil front suspension in an American SUV.

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If he was aiming down the sights correctly and had plenty of practice rounds under his belt, there would only be one side of this story.
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post #6 of 9 Old 12-29-2009, 08:31 AM Thread Starter
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Thanks for the feedback! I'm able to vaguely picture the problem now, and why it is more likely to bind. I assume this is why these systems usually use two sets of flex joints, one set at the frame end and one set where the radius arm attaches to the main arm.

I think I've got it, but my brain is having trouble wrapping completely around the range of motion during articulation and why binding results. I would think the flex joints on the frame end of the main arms would allow the necessary rotational twist, but I'm probably missing something. You guys would know best!

I'm suprised they are so popular on a lot of high-end TJ systems.
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post #7 of 9 Old 12-29-2009, 09:21 AM
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Quote:
Originally Posted by X-Defector View Post
Thanks for the feedback! I'm able to vaguely picture the problem now, and why it is more likely to bind. I assume this is why these systems usually use two sets of flex joints, one set at the frame end and one set where the radius arm attaches to the main arm.

I think I've got it, but my brain is having trouble wrapping completely around the range of motion during articulation and why binding results. I would think the flex joints on the frame end of the main arms would allow the necessary rotational twist, but I'm probably missing something. You guys would know best!

I'm suprised they are so popular on a lot of high-end TJ systems.
Just for visualization, use your arms and hands as the radius arms. Your shoulders are the flex joints at the frame, your hands are the two points at the axle. Grab a broomstick or something to be the axle, and move it around. If both your hands move up and down at the same time, everything moves fine and is happy. If one goes up and the other down, you'll have to move one or both of your wrists to let it move. Lock your wrists, and you'll feel the twist in your palms. That's the motion the bushings need to absorb.

They can and do work well, and are very simple--but they have their drawbacks, as already noted.


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post #8 of 9 Old 12-29-2009, 10:20 AM
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You can also think of it like a backward swaybar.

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Originally Posted by Jscwerve View Post
This is exactly why we need to practice proper gun control.

If he was aiming down the sights correctly and had plenty of practice rounds under his belt, there would only be one side of this story.
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post #9 of 9 Old 12-29-2009, 11:22 AM Thread Starter
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Thanks fellas, that helps me understand the dynamics a bit better. Can't have too much knowledge!
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