Long Arm 4 Link or 3 link?

I'm getting ready to start my long arms soon. I pretty much know what I'm doing thanks to this site, but I had a few questions about the link system.

I like the 4 link long arms like Rustys that uses the tabs from the LCAs with the UCAs branching off. Seems popular way to build these among most.
How long do these UCAs need to be? Can I buy regular short arm adjustable UCAs and use these as UCAs branching off my long arms?

Also, the Krawler kit is nice. I like the three link too?
Why do most builders opt to go with the above described 4 link?
In the 3 link set up, where does the UCA mount?? Is it in the center? Or is it mounted at an angle off to the passenger side inner body rail?

Are 3/4" heims too small to use for UCAs??

What you've described is not a 4-link. The two "upper" arms are fixed and only react to the braking and wrap torque so they don't count - hence, it's just a typical radius arm setup. People build this because it's simple and requires the least modification to the stock components to work.

It's definitely not the optimal system. It tends to unload easier on hill climbs and sidehills, it can have some interesting dive characteristics on the road depending on the angle of the arms, and if you keep both upper arms in place there's a lot of inherent binding. If you're building your own it'll help to make those uppers as long as possible - but this won't change the characteristics of it, just reduce the binding. With two uppers use rubber bushings all around or risk tearing off the stock axle mounts.

3/4 heims are more than adequate, but you don't even really need to use heims there as that joint doesn't move. It's a fixed triangle. You can use a threaded bushing there instead. I'd leave it adjustable so you can tweak your pinion and caster angle.

The 3-link is a whole nother world. Lots more possibilities for tweaking but also a lot more possibility for screwing up. If you're seriously considering doing this by any means other than buying a kit, do a lot of research and look for the "URF" threads from the likes of CRASH and Jes.

I'm interested in the answer to this question as well. I believe the original question was should you have arms on both sides running from the upper mount to the lower arm, or can you get away with only putting a single upper arm to the lower arm such as if you are using a D44 and don't want to build the bridge over the pumpkin.

Thanks,
Joe

I have run both a 3 link system and a singe radius arm system. I liked the 3 link alot more, but you have to be very careful to get your anti squat/dive set up correctly, otherwise you can get alot of body roll while under heavy braking. This happens because the torque from eh axle is only transmitted to one side of the chassis, causing it to twist. When I built my 3 link, I made sure I had about 100% anti dive/squat in the suspension, I ended up with 104%, and loved it. The jeep stayed perfectly level under braking, and I had almost no brake dive. I have since replaced the 3 link with a single radius arm on the passenger side due to clearance (and laziness) issues after swapping in my HP44. I do not like the radius arm nearly as much as it has some strange characteristics under heavy braking, but my jeep is not a daily driver any more, and the only time it sees speeds over 45 are on a trailer.

vetteboy said:

What you've described is not a 4-link. The two "upper" arms are fixed and only react to the braking and wrap torque so they don't count - hence, it's just a typical radius arm setup. People build this because it's simple and requires the least modification to the stock components to work.

It's definitely not the optimal system. It tends to unload easier on hill climbs and sidehills, it can have some interesting dive characteristics on the road depending on the angle of the arms, and if you keep both upper arms in place there's a lot of inherent binding. If you're building your own it'll help to make those uppers as long as possible - but this won't change the characteristics of it, just reduce the binding. With two uppers use rubber bushings all around or risk tearing off the stock axle mounts.

3/4 heims are more than adequate, but you don't even really need to use heims there as that joint doesn't move. It's a fixed triangle. You can use a threaded bushing there instead. I'd leave it adjustable so you can tweak your pinion and caster angle.

The 3-link is a whole nother world. Lots more possibilities for tweaking but also a lot more possibility for screwing up. If you're seriously considering doing this by any means other than buying a kit, do a lot of research and look for the "URF" threads from the likes of CRASH and Jes.

Click to expand...

With radius arms the length of the upper arms has "ZERO" effect on binding.

barillms said:

How long do these UCAs need to be? Can I buy regular short arm adjustable UCAs and use these as UCAs branching off my long arms?

Click to expand...

Yes,I run a set of RE adj's on my set-up.

RCP Phx said:

With radius arms the length of the upper arms has "ZERO" effect on binding.

Click to expand...

The binding is still present, sure. The difference is that you've got a larger distance to spread the bushing deflection over, so you can get a little more travel before the bushings start inhibiting articulation.

vetteboy said:

The binding is still present, sure. The difference is that you've got a larger distance to spread the bushing deflection over, so you can get a little more travel before the bushings start inhibiting articulation.

Click to expand...

so why not run jhonny joints or heims to change that??

VegasAnthony said:

so why not run jhonny joints or heims to change that??

Click to expand...

The binding isn't in a degree of freedom that JJ's or heims help in. This is why folks will run only one "upper" arm, or a wristed radius arm...because what needs to change is the length of one of those uppers (specifically, at least one lower arm needs to be able to pivot on the bolt that connects it to the axle).

i would go with joints larger than 3/4" heims. i ran a radius arm setup with 3/4 heims at the frame end. never had any problems but i was always worried about them. this past year i've switched to Johnny Joints with 1.25" shank.

So I'm guessing it's possible to run only one of the uppers to the lower, does anyone have any experience what the side effects of this are and how severe it is? I understand that there is some concern about brake dive on the non connected side due to torsional twist, but are there any other drivability issues with such a setup? Also, would there be any reason not to move the 'upper' link more towards the center of the axle to counter some of the problem?

I built a radius arm set up with only a pass side upper and it works GREAT!!! I used .250 wall tubing and johnny joints for all attachment points and I couldn't be happier. Do some reading on here, there's enough posts on this to make your eye's bleed.

I haven't had a chance to flex it alot yet but what I have done is VERY promising. For example, when the front end was on its springs with full weight on the tires i hooked up the trac bar with one finger. As in it wasn't lined up so instead of a HUGE rachet strap to pull the front end over I put one finger on the fender and pushed the entire front of the truck over 6+ inches!!

I really like the 4 link setup from Full Traction. Thats what I run and I have yet to be in a situation that I'm unsure what the suspension going to do. I would tell any one to take a serious look at their kit. Advice get there skidplate also, Badass. Very happy. Act as if you don't see the hood/intake mod... An idea gone bad, lol now I'm running an airaid intake.



Those are the 6.5in Springs that came with the kit. I'm now running 4.5in RE springs. I feel much more stable on steep hill climbs. Also one thing I think alot of people over look is the geometry of your steering arm and track bar. If they are on the same plain it reduces steering related issues. As you can see I don't need to run a steering stablizer.

-Nick

Nick.....I hope I'm not high jacking the thread but since you brought it up, which steering are you using? Wj knuckles? Uturn?

TeraFlex knuckle and steering arms.

Another high jack, what kind of rock sliders are you running? How do they work with the Full Traction long arm brackets? Do you have any pics of how they mount up? Thanks!

They are AJ's offroad Armor the super sliders. I had to mod the front mount around the long arm bracket. They mount I think 3 or 4 places along the unibody and then completely across the pinch seam. I'm at work now but I can take some pics when I get home and post them. But I really like them alot they make a good pivot point around trees and rocks.