sean21

Hey everyone. Not quite new to the forum but first time posting something. I'll give everyone a quick overview of what I'm doing but the main reason for this is to get insight on if there is a prefered length for the uppers on the radius arm setup I'm building.

Ok. I've got a 99 4 door xj classis with the np231 and hp d30 that I'm setting up for 5.5" of lift using RE coils and Leafs as well as doing a custom radius arm front with WJ brakes and steering with 4.88 gears locked front and rear. I've swapped out the 8.25(yes it was even the 29 spline) for a D44 out of a commanche that I converted to discs from the 8.8 ford axle. I've already installed an AA HD SYE and hooked up the longest front shaft with a double carbon joint found in the ZJ.

I've built my crossmember which incorperates some RuffStuff frame end link brackets that sit under the frame rails. I'm using Ruff Stuff Link brackets to replace pretty much every suspension/trac bar bracket on the jeep.

For the Front I've already built my D30 with new cromo shafts, Yukons gears and a spartan locker. Also have already set it up with WJ knuckles, steerting, brakes etc.

I've searched for ages, and considering I've already done a tonne of complicated stuff, I kinda hope not to sound like a noob. But. Is there a preffered length to the upper arms in a radius arm system? I'm not asking for length measurements, but a ratio or general distance up the lower links from the axle.

I'd post a pic(I have hundreds so far and all pretty cool stuff, will have to make a real build thread when I'm done) but I'm not sure how. Maybe thats my noob worthy statement.

Anyways, anyone have input for upper arm length for my radius arm longarm front suspension?

Cheers,

Sean

oh ya, hope advanced is an appropriate section.

Lead Foot

No matter how short or long the upper links on a radius arm are; it will not change the geometry and range of travel the suspension cycles through. The whole front axle will only be pivoting from each joint at the frame side. What you need to consider is strength if you are stuck on a radius arm design. All the upper links are doing is stopping the axle from rotating when torque is applied. (axle wrap). For strength purposes I would suggest the ange of the upper link referenced from the bottom link be 45 degrees or less. That is the length Of the link is long enough to meet the bottom link at a 45 degree angle or longer. It could even connect all the way back by the frame joint, all though this would be a waste of unneeded material.

Lead Foot

Better yet. Build a y link. Radius arm on one side, only a lower link on the other. Less binding and chance of breaking that 8mm bolt that goes through the upper axle mounts. It's the closest you can get to a 3 link without building a 3 link.

93XJLI

you're pretty much 100% wrong. people interchange radius arm and y-link (bc theyre the same really.. a "real" radius arm is technically a wristed radius arm). the "3 link y-link" that IRO sells and that you're talking about is still a y-link, and NOT a 3 link... it still binds just as bad as a TNT/clayton/RC/whatever y-link radius arm.

and radius arms change caster throughout travel, so they do change your geometry as the suspension cycles. so you're wrong again. and you're talking about axle wrap in the completely wrong sense. please just stop talking.

OP, they dont need to be long. 18-22" is fine, or a little over 1/3 of the length of the lower. i've seen plenty of people take an adjustable upper short arm and use that as the upper arm in the y-link. just make sure one end is adjustable so you can play with caster/pinion angle.

Lead Foot

Umm excuse me. I NEVER said a "y-link" was or is a 3 link or is just as good. I simply said a "y-link" is the closest you can get without going 3-link, which is 100% TRUE. Also, a "y-link" DOES have less inherent bind then your standard "radius arm". This is also 100% TRUE.

Don't get me started with you trying to not pick about the incorrect terminology that gets loosely thrown around these days. The term 3-link is not even used to refer to what is technically a 3 link. It is used to refer to a 4-link! The term 4-link is openly used to refer to a 5-link system. So dont try to make some point and talk down to me about the term wrist pin/wrist arm verse radius arm! I am simply using the terms that readers have accepted and understand as true for ease of communication.

I never Once said that a RADIUS ARM setup does not cause a change in CASTER through travel. I stated that A LONGER OR SHORTER UPPER ARM WILL NOT MAKE A DIFFERENCE IN THE GEOMETRY OF A RADIUS ARM SETUP SINCE NO MATTER WHAT IT WILL STILL ONLY PIVOT FROM THE 2 FRAME SIDE LCA JOINTS. This is also TRUE and you need to Reread what I posted.

I never once mentioned the effect on radius arms and the change in caster because the OP did not ask the difference and pros of a 3-link vs radius arm setup. I AM HOWEVER talking about how the upper arms are there to STOP THE AXLE FROM ROTATING. On a leaf spring system this is known as AXLE WRAP. Axle wrap can even happen on a linked system if link joints are worn out, specifically the rubber and poly bushings.

93XJLI, it seems you have looked at my number of posts, saw that you have posted 180X the posts that I have, then proceeded to skim over my helpful response , take some of my words out of context then twist them into what you wanted them to mean so that you can make yourself sound smart. Either that or you just somehow completely misunderstood my whole post.

What you need to do is realize that I am mechanical engineer graduate. I have designed, machined, fabricated, and tested my own suspension products for 8 years. Built and ran my own successful XJ offroad suspension business as a hobby. (my best selling product being a long arm TRUE 3 link upgrade shipped to over 15 states) and built many custom linked jeeps in my own shop.

Knowing this, Reread my whole post and tell me how stupid I am again.

Thank you for your time
Kris

93XJLI

panties in a bunch, eh? and dont flatter yourself, i wasn't stalking your previous posts

3 link, y-link, panhard shamhard. tomato, tomahtoe... amirite?

Lead Foot

Sorry if I came off a little strong. It's 12:15 here and I'm extremely jet lagged from my previous travels and can't sleep so I'm browsing around the forum. I'm probably a little cranky.

N20jeep

The iro kit does not have the binding issues of the normal radius arm kits. Eliminating the one upper is what stops this.

N20jeep

And to the Op's question.

I make the uppers on any of the tj/xj/zj longarms I build at around 18"

gilbertxj466

Just watch your caster, by getting the bump stops centered in the coil springs.

93XJLI

It's still a dumb way to build long arms

N20jeep

Imo, the only thing that's not very good about the iro design is the caster adjustment. I think it could have been designed different.

Otherwise the kit rides and performs great on the xj's I know with it.

sean21

Thanks for all the replys. I understand it theoretically doesn't change any way the front end reacts by having one length vs another on the uppers. My thing was the very fact of strength. If having a longer upper was stronger than a short upper or visa versa.

Regadless, I will be eventually converting it into a true 3 link later down the road(I already have an axle end link tower sitting idle) but I wanted to start out with a radius setup as I'm not quite ready to hack off the stock upper link brackets. Basically this truck is going from bone stock to everything I described earlier all at once. I want to start with a radius arm first to then see how everything works together and determine first hand how it needs to evolve.

Also, it's being used for work primarily(I work for a mineral exploration company that requires me to wheel all day long for 4 months outa the year. Sucks I know. lol) and figured a radius arm would be the safest(reliable/most reversable) way to get this project going. I've been bustin my *** for the last 4 weeks getting everything co-ordinated and need to complete it in the next couple weeks. I just need to get the front end under it, build my roof rack, and get it into my local 4x4 shop for gears and lockers.

Any further input or ideas is more than welcome. I'll put together a build thread when I'm done running around with my head cut off. Looking forward to that!

ktmracer419

Longer uppers= less stress on the upper joints and mounting points. As long as they are at least the same length as stock uppers i wouldnt worry about it.

ktmracer419

And even without the binding i wouldnt trust one of those keeping my axle in place.