4-link vs. radius arm lift - Ford Powerstroke Diesel Forum
Suspension & Steering Discuss OEM & aftermarket suspension, lifts, air ride suspension, shocks, steering components, etc.

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  #1  
Old 09-12-2012, 07:51 AM
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Arrow 4-link vs. radius arm lift

hey everybody i was wondering what the difference in a 4-link and a radius arm lift kit is before i go and buy the wrong one. i plan on putting it on my 2008 f250 and will rarely be going off road so which do yawll recommend?
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Old 09-12-2012, 11:08 AM
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Radius arm......

4 link will be for more articulation, travel. not needed on street driven truck. besides the steering setup not being IDEAL for 4 link, keeping with a radius arm helps truck return to stock form as well.
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Old 09-12-2012, 12:14 PM
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I wouldn't run a 4-link on an axle that has its steering designed around a radius arm setup.

Not trying to start a battle here but here are my thoughts. Some don't agree but here you go.

1) The OEM steering is matched to a 3-link not a 4-link. If you put a 4-link on your truck you will probably get bump steer and you will feel it it in the steering wheel. It will also add additional stress on your steering box, drag link, and track rod as well as your ball joints. It does the same thing as changing a pitman arm and not changing the track rod bracket.

2) The rubber bushings in the axle are not designed to twist like the 4-link needs them to, so the bolts are going to work loose or it will tear up the bushings. Those big rubber bushings don't magically turn into uni-balls. They were not built to be used like that.

3) The 3-link is part of a sway bar system and putting a 4-link on a truck that came with a 3-link will require a bigger sway bar because there will be more body roll.

4) An item that may not be a large factor but still should be considered is at full suspension droop. The U-joint is at more of an angle on a 4-link and could bind up and cause a drive shaft or t-case failure.
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Old 09-13-2012, 01:11 PM
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In our personal opinion, we would run a 4 link! But everything must be taken in context!

The OEM steering geometry - track bar to drag link relationship is really good on 05+ Super Duties so as long as the aftermarket suspension geometry is good, bump steer will be as it was from the factory!

As layson stated, you need to be aware of your drive line angles for the suspension travel! This must be paid attention to both at the t-case and the axle connection. A radius arm system will maintain a better u joint angle at the axle connection, but it will still undergo the same angle at the t case for the most part as a "good" 4 link system and this will typically be your limit.

A "good" 4 link system will offer a much more consistent caster curve so the handling over bumps should be more consistent.

The rubber bushings at the axle actually see less stress with a 4 link than they do with a naturally binding radius arm setup as offered by the factory and typical aftermarket!

A 4 link system will require shocks and springs to be tuned with it as a 4 link system loses the natural binding or torsional rigidity offerred by the stock radius arm configuration.

What kind of height are you looking at lift wise and budget wise. Those are probably the most important factors!

JP
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Old 09-13-2012, 05:33 PM
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I am looking to put either an 8" or 10". I'm wanting to run 38/15.5/20 tires, but want the smallest lift that those will fit under. And my budget isn't very big. That's why I was thinking the Rough Country 8" because I believe those tires will fit under an 8" and it's only $1,500.
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Old 09-14-2012, 06:29 AM
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If you want good prices on our systems, try CT Performance on here or 8 Lug Truck Gear! Our 8" Triple Threat is a nice system and it includes mini packs in the back as well as all the hard parts up front with a great 4 link conversion.

JP
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Old 09-17-2012, 09:29 AM
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JP, Had a nice long weekend. Dang do we really have to do this again? Come on! LOL


Quote:
Originally Posted by Pure Perf View Post
In our personal opinion, we would run a 4 link! But everything must be taken in context!

The OEM steering geometry - track bar to drag link relationship is really good on 05+ Super Duties so as long as the aftermarket suspension geometry is good, bump steer will be as it was from the factory!

There is no bump steer from the factory, until you cause it with a 4 link.

You gotta at least tell me that the path the axle travels with respect to the frame is a heck of a lot different between a radius arm and 4-link setup? The radius arm travels in a very simple path compared to a 4-link. You are still retaining the factory axle motion that the steering linkage was designed for. Your caster is constantly changing with a 4-link…. So what if your drag link and track rod relationship is perfect? Get your drag link and track rod relationship perfect, then just try rotating that front pumpkin around to different positions and go drive the truck. I don’t think you even need to look for any bumps to see how well the truck steers. Take note that the “track bar to drag link relationship” is not the main reason you get bump steer. A common misconception is that them being parallel is really the only thing that matters when it comes to bump steer. Go to different truck dealerships and look at the trucks on the lot and you don’t even need to take any measurements to realize that they are in fact not.


As layson stated, you need to be aware of your drive line angles for the suspension travel! This must be paid attention to both at the t-case and the axle connection. A radius arm system will maintain a better u joint angle at the axle connection, but it will still undergo the same angle at the t case for the most part as a "good" 4 link system and this will typically be your limit.

If you pick the truck up on a lift the front drive shaft will bind and can break at the yolk. When you simplify critical things like joint angles and say the T-case joint angle will be the same on both set ups when they will NOT be the same, is simply bad advice. Do you have any pictures showing this? Another thing to mention that if you have to defensively drive to avoid an accident since you are running a 4-link and your tire goes up in your fender you are going to have a bad day. Just because you don’t jump your truck does not mean it should not function correctly.

A "good" 4 link system will offer a much more consistent caster curve so the handling over bumps should be more consistent.

What do you mean by handling over bumps, what are you talking about? Please explain this because it doesn’t make much sense to me. What do you mean caster curve in bumps? Are you talking about going around corners in bumps?

Have you had a chance to ride in a “good” radius arm setup? Consistency is in a radius arm setup, the path is consistent, a 4-link is always changing. A “good” radius arm setup just drives good all the time. There are no bumps in the steering wheel. It drives like a car.


The rubber bushings at the axle actually see less stress with a 4 link than they do with a naturally binding radius arm setup as offered by the factory and typical aftermarket!

I am just curious how the radius arms “naturally bind”? Are you talking about the fact that a designed radius armed setup is going to be slightly stiffer than a 4-link setup that is put on a truck that had a radius arm suspension? The truck now is naturally going to have more body roll since the sway bar was not changed out.

As far as the bushings go. When one wheel travels up in the wheel well and the other droops down, think about how the relationship is with the 4-link arms. The link arms want to stay perpendicular to the centerline axis of the axle as it is shifting up on one side and down on the other. That translates down the link arms and has to be able to be alleviated in the connection at the frame. There are (4) points at the frame that have to allow some type of rotation/twisting, if there is, then it has to be less stiffer than the bushings at the axle. Most likely the bushings at the axle will have to take this rotation. Even your companies setup doesn’t allow for rotation, It is fixed at one end with the motion of the axle and then no real way for them to rotate at the frame (well I am sure you have retighten those jam nuts ) I would bet that your bushings in your joints are probably stiffer than the ones in the axle. Which would tell me that those bushings at the axle are taking the most rotational load. These bushing are designed by Engineers at Ford to do one thing and you guys are trying to make them magically be a uni-ball, the bind is more a 4-link set up than on a 3 link because you are twisting the bushing in a knot during wheel travel.


Now a “good” 3-link, radius arm setup has the ability to take this rotation at the frame. It also has the ability improve the factory setup dramatically. The bars are offset and enable you to have a tighter turning radius than stock. You can dial your castor in to retain your factory steering with NO bumpsteer. The expensive joints enable the suspension to feel tighter without any of that factory wander. That is why I recommend these.


A 4 link system will require shocks and springs to be tuned with it as a 4 link system loses the natural binding or torsional rigidity offerred by the stock radius arm configuration.

Remember that when you put a 4-link on a truck that was designed with a radius arm setup with a designed sway bar the truck it is going to be less “stiff.” So now you need stiffer springs and a monster sway-bar to control the increased body roll that was added to the truck. Does that come in the kit?

What kind of height are you looking at lift wise and budget wise. Those are probably the most important factors!

JP
To recap,
If you take off your radius arms and bolt on a 4 link, the negatives you will have…….

Bump steer, more Body Roll, maxed out rubber axle bushing, bound up U-joints, less turning radius, and possibly the inevitable death wobble

And you gain something that is not really tangible nor explainable = Better Caster curve in bumps.

What it all comes down to most of the time is some guys just prefer 4-links, even if it may not be the best thing for their trucks.
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Old 09-17-2012, 09:55 AM
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Layson

It is always fun.

You made some pretty bold statements.

I would love to hear your explanation for them...

If you take off your radius arms and bolt on a 4 link, the negatives you will have…….

Bump steer, more Body Roll, maxed out rubber axle bushing, bound up U-joints, less turning radius, and possibly the inevitable death wobble

And you gain something that is not really tangible nor explainable = Better Caster curve in bumps.


Also, while you are explaining your bold statements, what happens at the axle connection points with a radius arm system as the axle articulates? In particular the bushings!


JP
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Old 09-19-2012, 11:09 AM
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Ok, now I dont mean to hijack the thread slighty, but I was wondering the same exact thing, 4 link vs radius arm drop, but for my 2007 F250 CCSB. The kit i was looking at is the BDS 6''.

Now I know the trucks and lifts are different but do the statements still hold true? Also like the OP, I wont be doing much offroading but would like to occasionally. Itll will be a daily driver. So just wondering which option to go with, thanks for any help guys.
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Old 09-19-2012, 12:02 PM
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Personally and as a company, we feel 4 links are smoother since they do not have the natural binding points that radius arm systems have. So, when you hit a bump on one front tire, it is not transfered as hard over to the other side.

Keep in mind, when doing a conversion of this nature, you need to make sure the springs, shocks and entire system is tuned for it..

JP
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