What's so wrong with radius arms?

[98xjjeeper]

Sorry now I'm getting confused, I was thinking control arms this whole time then I realized we were talking radius arms so I looked it up to refresh my piss poor memory and this is what I keep seeing..Is that not a control arm?

Yes they are normally called control arms. Two lowers and an upper that attaches to one LCA. That is the same as a wristed radius arm setup, only one side keeps the axle from twisting the the other side just locates the axle. Often people miscall that a three link, since there are only "three links" but it isn't, its a wristed radius arm. You end up with great flex but you still have caster issue and the problem of it lifting the front end under a bind or climb. Three link is the way to go without a doubt if you want the best offroad performance, no binding, no axle wrap because you use hard joints, no lifting of the frontend on climbs and when the front end is in a bind. It also handles amazing onroad because of the same reasons. Those who say the radius arm setup is great on and off road compared to a 3 link haven't run a 3 link or a properly setup 3 link. Yeah it will drive fine and has been used for years from the factory but its not the most ideal. Its just a cheap and easy way of having longarms.

 

[redrider2911]

Sorry now I'm getting confused, I was thinking control arms this whole time then I realized we were talking radius arms so I looked it up to refresh my piss poor memory and this is what I keep seeing..

Is that not a control arm?

Explained in more detail. A 3 link has 3 individual control arms attaching at the frame at 3 seperate points and at the axle at 3 seperate points. A radius arm has upper arms that attach to the lower arms about half way through. Some over an upper link on both sides (more similar to a 4 link) or just an upper on one side, compared more to a 3 link.

A true 3 or 4 link means extra bracketry and more steel used for those brackets and longer control arms as well as the time to shape those brackets to fit around an XJs uniframe. This all means more money and time needs to be invested into developing and fabricating these types of setups. That is why most big corporations dont go this route. A radius arm only attaches at the frame at 2 mounts thus really only needed 4 tabs (1 on each side of each joint) that are somewhow attached to a plate mounted to the uniframe. Sometimes this means just 2 simple plates or a full crossmember.

Something else about radius arm setups. They usually use the stock 10MM bolt for the upper control arm at the axle. Since the setup creates more bind and puts more stress on that bolt I have personally seen many sheered right off during wheeling trips.

The good thing I have to say about radius arm setups are their simplicity. I radius arm will only put direct force on a uniframe at the mounting location. ie pushing and pulling stress. A poorly designed 3 or 4 link puts more of a twisting action on the frame from the pushing and pulling between the upper and lower mounts stopping the axle from rotating.

 

[RCP Phx]

Castor isn't even an issue "on the road" and who cares when off-road.Ive got 10yrs on both my DD's with radius arms(w/ 2 uppers) and have never had any issues.Is there binding,yes,has its caused any problems,no.

 

[whitetrashxj]

I am working on some eb radius arms for my buddies Nissan Hardbody right now, do you have a pic or description of how you wristed the psngr side arm? Do they have a bend in them to make them parallel to the unibody rails? Thanks!

got anymore pics of this? im going to be doing the same thing in my xj but trying to adapt them to my rubicon express crossmember, hopefully i can, might have to cut off the pass side wedge and move it over or wrist the arms outward

trying to find info on this kinda setup is like beating a dead horse, kinda pointless cause im not finding anything
nick

 

[bails85]

Castor isn't even an issue "on the road" and who cares when off-road.Ive got 10yrs on both my DD's with radius arms(w/ 2 uppers) and have never had any issues.Is there binding,yes,has its caused any problems,no.

Caster is a huge issue on the road. It keep you from swaying around. I'm not talking about death wobble. Having correct caster makes the vehicle act less like a boat.

 

[Beezil]

Kony runs radius arms

 

[slappomatt]

OH snap! lol.

I have the iron rock 3 point radius arm long arm kit. Their kit addresses the binding by removing one of the axle mount points. Still have caster issues. But it doesn't seem to be very noticeable. After I get the rear to be at least as good as the front ( I am going to 4 link the rear and I have some 14" coilovers going on the rear.) I am going to order a 2nd passenger side single lower arm, flip it and make a upper arm and have a 3 link setup which should address the caster issue.

 

[Darky]

I wouldn't not run radius arms, but I decided to go with the Rock Krawler 3 link instead. I was more comfortable with the overall design. My only complaint is it gives up a couple inches of ground clearance over the radius arm since it mounts under the frame, but I've only drug the mounts a couple times and they have yet to hinder me off road.

 

[RAM-ROD]

It seems radius arm set up are used due to people having a HP 44 with cast wedges. I happen to have the same axle. My question is if you can weld to the stock radius arms why not cut them as short as possible and then weld your lower control arm mounts to them and mount upper conrol arm mounts to the axle like a standard 3 or four link?

 

[Vanimal]

might be a stupid question but i swear i see it done this way in some pictures... are people just removing the passenger side upper link on the radius arms like the blue one in the other pic? is that strong enough with something like a RE radius arm setup?

 

[SC Rednek]

might be a stupid question but i swear i see it done this way in some pictures... are people just removing the passenger side upper link on the radius arms like the blue one in the other pic?

Yes, that solves the binding problem during flex, but not the changing castor

trying to find info on this kinda setup is like beating a dead horse, kinda pointless cause im not finding anything
nick

excellent job resurrecting a VERY dead thread WhiteTrashXJ!

and the reason you're not finding anything is because radius arms are retarded. :dunce: Save your pennies a little longer and do it right!

 

[old_man]

So SC_Redneck, have you ever driven a Ford Pickup? Millions are on the road and don't suffer from the problems you report. Yes the Caster changes when you hit a bump but it isn't enough to cause problems. I've run a Ford Based radius arms for over 100k miles of on and severe off road and I love it. I ran what we called long arms for years before that.

I'm an engineer by profession so I have learned to investigate what works and doesn't work for myself. I'm also a cheap bastard. I have a total of around $1100 in a D44 high pinion front end. That includes locker, gears, track bar, brakes, rotors, etc. I finally got a chance to snap some pix and I will post them here. It isn't fancy and it has 100k miles worth of grease and grime on it, I even commuted 150 miles a day to work with it for months. The street manners are great.

Ever heard about not using the crappy 78 D44 that has the cast wedges (that you can get cheap), well it works great with no mods and it even comes with the large disk brakes.

I rotated the coil buckets 180 degrees and ground the tops of the C's to point inward. The coils look a bit funny but as you stuff the tire, the springs actually straighten out.

I even took the stock Ford track bar and did a bit of straightening, then welded a coupling nut on the end and attached it to the track bar bracket.

For years I ran the setup on and offroad without wristing the passenger's side, but one day I got bored and converted it to wristed.

The welding on this was done about 10 years ago and was done with a 110v MIG. To enable the wristing motion, you simply pull the rear bolt.

On the driver's side, I stuck with the Ford shock mounting.

While it is entirely feasible to run the stock Ford rubber frame mounting, I went with a large RE SuperJoint on each side. The connection was made by welding a 1" grade 8 bolt to the joint, then I took a 1" coupling nut and welded it to the end of the radius arm after having taken off the stud with a saw. I added a strap on each side to strengthen the connection. Welding that thick stuff with a 110v MIG worked even if it left a messy weld. Have I mentioned that I love my 240v MIG now:wave1:.

I run a 4 degree set of polly C bushings to set my caster for stability on the road. Haven't actually measured what the resulting caster is, but it works find so I really don't care.

 

[SC Rednek]

So SC_Redneck, have you ever driven a Ford Pickup? Millions are on the road and don't suffer from the problems you report. Yes the Caster changes when you hit a bump but it isn't enough to cause problems. I've run a Ford Based radius arms for over 100k miles of on and severe off road and I love it. I ran what we called long arms for years before that.

Yes I have, and I would never willingly convert my jeep to that given a choice.

And no I really don't care about the castor changes either, I think the desert racer guys don't like it but they're talking about much more movement at much higher speed. Street manners have more to do with shock and spring selection.

The issue is the binding under FLEX (I'm talking one side up and the other side down, NOT hitting bumps and whoops). They simply don't flex, and yes I'm saying this from experience. But if you look at the geometery of a non-wristed radius arm, it makes perfect sense (go grab some broomsticks if you're confused).

Now, wristing one side like you did will fix that, since only the nonwristed side will be trying to set the castor. Or if you have y-link radius arms, removing one of the uppers does the same thing.

But my opinion, find the stronger, non cast wedge axles. For F150's the good years are '76 and '77. Mine's a '77, disk brakes, 1/2" thick, one piece axle tubes. And put on a 3 or 4 link. Might cost a couple hundred more, but it's a better design.

 

[Vanimal]

Yes I have, and I would never willingly convert my jeep to that given a choice.

And no I really don't care about the castor changes either, I think the desert racer guys don't like it but they're talking about much more movement at much higher speed. Street manners have more to do with shock and spring selection.

The issue is the binding under FLEX (I'm talking one side up and the other side down, NOT hitting bumps and whoops). They simply don't flex, and yes I'm saying this from experience. But if you look at the geometery of a non-wristed radius arm, it makes perfect sense (go grab some broomsticks if you're confused).

Now, wristing one side like you did will fix that, since only the nonwristed side will be trying to set the castor. Or if you have y-link radius arms, removing one of the uppers does the same thing.

But my opinion, find the stronger, non cast wedge axles. For F150's the good years are '76 and '77. Mine's a '77, disk brakes, 1/2" thick, one piece axle tubes. And put on a 3 or 4 link. Might cost a couple hundred more, but it's a better design.

you cant find them, plain and simple. i've been looking for almost 5 months, not even an overpriced one has poped up. maybe in EBF they have a ton of old trucks kicking around, but here they generally have already been crushed and/or stripped of the axles. I have the same axle as old man, however i opted to retube it.

 

[SC Rednek]

Just some quick math, if you have 36" long radius arms (I'm just guessing, don't know the exact length you can set me straight here Old Man), and 16" of travel per wheel (not unreasonable for a rock crawler), that's 26.4* of castor change throughout the range of travel.

In a non-modified radius arm design, that 26.4* of binding while flexing will have to be absorbed in the bushings in order for that flex to happen. Good luck with that.

 

[SC Rednek]

you cant find them, plain and simple. i've been looking for almost 5 months, not even an overpriced one has poped up. maybe in EBF they have a ton of old trucks kicking around, but here they generally have already been crushed and/or stripped of the axles. I have the same axle as old man, however i opted to retube it.

I found mine rotting away in an old truck junkyard in Northern Ohio. Cost me $250. Yeah they're hard to find, worth the wait though.

 

[old_man]

Opinions differ. Stronger non cast wedges? I would argue that they are just as strong if not stronger. Lack of flex, well I have run just about every trail in Moab and a ton of the hardest trails in Colorado with this so called lack of flex. Flex for flex's sake is very overrated. Looks cool on an RTI ramp.

 

[SC Rednek]

Opinions differ.

Yes. And mine is right!!!

Stronger non cast wedges? I would argue that they are just as strong if not stronger.

'76 and '77 have 1/2" (with a few '77s only 3/8") thick axle tubes.

'78-'79 axles had 3/8" or 1/4" thick axle tubes, pressed into the hollow, cast wedge section on either side, so basically a three-piece axle tube.

Lack of flex, well I have run just about every trail in Moab and a ton of the hardest trails in Colorado with this so called lack of flex. Flex for flex's sake is very overrated. Looks cool on an RTI ramp

You have a wristed arm, so you don't bind during flex.

And besides, what good is a jeep if you can't look cool?

 

[old_man]

I did all those trails without the wristed setup.

 

[SC Rednek]

And I've done Gold Bar Rim and Golden Spike with short arms, open diffs, and a broke track bar. With as much traction as those rocks have, not saying much!