4 link for dummies

[earlybronco72]

My lowers are going from the D20 out put yoke to the axle (about 4" outside of the frame, with the axle pushed back 3" from stock), and they're going to be 41.47". My uppers will be 28.72" My 2.25" DOM was $13 (+/-) a foot.

Is this 41.47" from joint to joint, or is this just the length of the tubing? I have my lowers mounted at the output, and the axle moved back three inches, and my lowers are 48" long. Do you have a 203 in there also?

[720Racer]

Is this 41.47" from joint to joint, or is this just the length of the tubing? I have my lowers mounted at the output, and the axle moved back three inches, and my lowers are 48" long. Do you have a 203 in there also?

41.47" from joint to joint. Not actually at the output, but at the center of the CV. The bracket for the lowers at the axle puts the joint about 3.5" forward of the axle tube. No 203, but ZF5 and D20, it's supposed to be only a few inches longer than stock.

[720Racer]

The Flex Joints I'm using are made by Summit Machine. The have a new joint called a Jimmy Joint , it's basically a rebuildable heim joint with 60* of misalignment (as opposed to the 30* Flex and Jonny Joints have). Bad Ass, I'm already wishing I was using these, and I haven't even bolted mine on yet.

[71BRONCO71]

Lets start with the basics and go from there. Like calculators, center of gravity, anti squat, anti dive, etc... Maybe a recommendation on a basic parts list. Or anything else that you can think of that might be helpful.

Let the learning begin! Class is in session!

Drop it off at Silly's shop? and hope your wallet doesnt run away? hahahaha
Heres a "Dummy link question":
now i got the basics down (I think), but what springs do you use... coilovers, coils, leafs?

[720Racer]

.....what springs do you use... coilovers, coils, leafs?

Depends on what you can make work. I think most use coilovers, coils or air shocks. I've heard you can turn your leafs into 1/4 elipticals, and use them as well. Price wise, it would go coils, then air shocks, then coilovers.

[Delta 4 Wheel]

Drop it off at Silly's shop? and hope your wallet doesnt run away? hahahaha
Heres a "Dummy link question":
now i got the basics down (I think), but what springs do you use... coilovers, coils, leafs?

Yep. Maybe just what I will do.

[welndmn]

Follow someone on the trail, and watch how theirs works.
If you like, measure it and copy it.
I spent over a year rewelding mine until I got how I like it.
I should of just stolen someone elses work.

[crawlin68]

Well Galen informs me 2.25"OD x .375 wall is available.

I've been checking around for the best price on some of this. How much do you think we need to buy if I can buy it by the foot? If all else fails, we can just buy a 20' stick. I would like enough to build 2 lower links and a third link to carry as a spare.

[Sillyneck]

crawlin68
-cost vs. strength for your bronco and set up....

you'll be fine w/ 2" .250 dom. 1.25" heims w/ tube adapters fit in the ends no prob.

for the uppers 1.5" .250 tube w/ 7/8 heims.

No drilling, no tapping no bs. the back of an eb is the easiest 4 link ever. depending on what coils you have up front you should choose the same exact coils for the rear. stock upper buckets and lower retainers work fine... you can add adjustability to those to fine tune it. since the frame is the same width front to back if you put the coils on the back the same way you're more likely to have a perfectly balanced suspension system. The rear will likely overwork the front because your front isn't linked the same way.

If you need any of these supplies let me know. I get good deals on all the materials.

[crawlin68]

crawlin68
-cost vs. strength for your bronco and set up....

you'll be fine w/ 2" .250 dom. 1.25" heims w/ tube adapters fit in the ends no prob.

for the uppers 1.5" .250 tube w/ 7/8 heims.

No drilling, no tapping no bs. the back of an eb is the easiest 4 link ever. depending on what coils you have up front you should choose the same exact coils for the rear. stock upper buckets and lower retainers work fine... you can add adjustability to those to fine tune it. since the frame is the same width front to back if you put the coils on the back the same way you're more likely to have a perfectly balanced suspension system. The rear will likely overwork the front because your front isn't linked the same way.

If you need any of these supplies let me know. I get good deals on all the materials.

Thanks for the info! I have thought about 1.5 x .250 wall for the uppers, only because I have a 10' section of it left over from my steering build. So you think that will be plenty strong for the upper links? I do like the idea of having the upper and lower links all have 1.5 ID so all 8 joints would be the same and interchangable and I could carry one extra joint (or parts if they are rebuldable) in case I need to do a trail repair.

[Sillyneck]

naw I was saying 1.5" uppers and 2" lowers. 1.25 heims in the bottoms and 7/8 up top. If you want to spend the money on all 1.25 joints then rock on... but the 7/8 and 1.5" comes in at 1/2 price... considering you have more than enough 1.5" as it is.
you won't need an extra 1.25 heim and the 7/8 uppers are borderline overkill. The'll never see rocks or abuse and if you don't have any bind in the suspension and it's set up mint you'll never see one fail.

If you destroy a 2" .250 lower link in your application you'll be more concerned about the life flight bill than you will getting the rig out LOL

As far as upper link strength... you could get away w/ .120 wall. I don't suggest it but I have seen as thin as .95 x1.25" hrew tube survive up top. Grady's top truck willys actually had those upper links. I was amazed when I went to grab one off the floor like it would weigh 15lbs and I about threw it over my head lol.

[Lars]

Quote:

Patrick, I thought I would post this over here to keep your Moab thread from getting to cluttered with 4-link info.

Yes, the DOM I have is 2" OD .250 wall. For the .375 (3/8") wall DOM, I'm not sure they make a it with a 1.5" ID (the size of my inserts) We would need 2.25 OD x .375 wall. They make 2.5 OD x .5 wall, that's getting pretty big. The shafts on JJ are 1.25" so 2" x .375 would have an ID of 1.25 not big enough for inserts.

I'm not sure what I should do now, In the link calculator they calculate the loads on all the links (click on the material tab) and give a factor of safety (FS). With 2" x .250 wall they are 9 and 15 times the calculated loads for compression and buckling, but the bending is 1.16 times. A FS of one is equal to the load it would take to bend the link with 1/2 of the broncos weight sitting on one lower link. In this case 2500# (I am estimating 5,000# for my bronco, it is probably closer to 4,800)

Now (if I didn't lose you already) with 2.25 OD X .375 wall (assuming we can get it) the FS goes up to 1.94. And 2.5 OD x .5 wall goes to 2.8. Open up the calculator and play with it you enter any size tube and even change material types. Keep in mind these will vary based on vehicle weight and length of the links.

Now, I guess the question is what FS is safe, maybe Lars could provide some insight. My engineering background is all in Civil engineering, so if we wanted to support a snow or wind load I would know what to do. On another thought the Cage/JD arms are only .250 wall ( I think). And Lars was comfortable making is new Radius arms w/ .250 wall.

Wow, a lot of good information in a hurry.

Without knowing anything else, I'd immediately vote for a FS of 2, minimum. FS of 1 means that theoretically you could reach that load under static conditions (not moving). At that point you are at the design limit. FS of 2 means a 2G (acceleration) hit in the direction of interest.

As an example, when I was pondering my radius arm design before I built them, I wanted to use Johnny Joints for the rod ends, but I balked at first because they only use 9/16" bolts. I figured on sustaining a 10G direct front end hit. At that point you have other concerns, including possibly the life flight that sillyneck mentioned! At that point a 9/16" bolt would see about 50,000 psi, which is still less than the yield shear strength of a grade 8 bolt. So the factor of safety of those bolts is better than 10. I stopped worrying and built the arms. If it had been a FS of 2, I would have done something different, since a 2G impact head on could be reached just slamming a boulder on the trail.

As for the 2" x .25" wall tube, I looked at the bending stiffness (which isn't the same as strength) and compared that to the stock arm. Those calculations get a little exotic if you aren't familiar, so I'll leave out the details, but the upshot was that the reinforcement I got from using stubs of the stock arms actually made my arms stiffer than stock up front. The stock arms taper, so they get less stiff as they go back. At the transition from arm stub + tube to just tube on my arms, they are as stiff as stock, and because they don't taper, they are stiffer than stock all the way back to the joint. So if I come down on a rock with a radius arm, I'm less likely to bend it compared to a stock arm. Laterally (sideways) there's no comparison between a round tube and stock. The tube is many times stiffer, and stronger. BUT... dent the tube and all bets are off. That's where extra wall thickness on the lower links gives a benefit. Given enough enthusiasm you can break anything. Come down on something hard enough and you can bend a solid steel 3" OD bar. Eventually something's going to be the weak link. I'd feel comfortable with 2" OD x .25" wall for rear links based on the way I drive. On the other hand, Mark has seen a lot more hard core trail time and breakage than I have, so as he implied, it might not be enough for everyone.

[Lars]

Follow someone on the trail, and watch how theirs works.
If you like, measure it and copy it.
I spent over a year rewelding mine until I got how I like it.
I should of just stolen someone elses work.

Mark-

Got any pics of your setup?

[crawlin68]

Wow, a lot of good information in a hurry.

Without knowing anything else, I'd immediately vote for a FS of 2, minimum. FS of 1 means that theoretically you could reach that load under static conditions (not moving). At that point you are at the design limit. FS of 2 means a 2G (acceleration) hit in the direction of interest.

As an example, when I was pondering my radius arm design before I built them, I wanted to use Johnny Joints for the rod ends, but I balked at first because they only use 9/16" bolts. I figured on sustaining a 10G direct front end hit. At that point you have other concerns, including possibly the life flight that sillyneck mentioned! At that point a 9/16" bolt would see about 50,000 psi, which is still less than the yield shear strength of a grade 8 bolt. So the factor of safety of those bolts is better than 10. I stopped worrying and built the arms. If it had been a FS of 2, I would have done something different, since a 2G impact head on could be reached just slamming a boulder on the trail.

As for the 2" x .25" wall tube, I looked at the bending stiffness (which isn't the same as strength) and compared that to the stock arm. Those calculations get a little exotic if you aren't familiar, so I'll leave out the details, but the upshot was that the reinforcement I got from using stubs of the stock arms actually made my arms stiffer than stock up front. The stock arms taper, so they get less stiff as they go back. At the transition from arm stub + tube to just tube on my arms, they are as stiff as stock, and because they don't taper, they are stiffer than stock all the way back to the joint. So if I come down on a rock with a radius arm, I'm less likely to bend it compared to a stock arm. Laterally (sideways) there's no comparison between a round tube and stock. The tube is many times stiffer, and stronger. BUT... dent the tube and all bets are off. That's where extra wall thickness on the lower links gives a benefit. Given enough enthusiasm you can break anything. Come down on something hard enough and you can bend a solid steel 3" OD bar. Eventually something's going to be the weak link. I'd feel comfortable with 2" OD x .25" wall for rear links based on the way I drive. On the other hand, Mark has seen a lot more hard core trail time and breakage than I have, so as he implied, it might not be enough for everyone.

Great insight Lars. So when you say a FS factor of 2 is recommened, are you talking about the bend FS factor or the buckling FS factor? According to Highlander, the 2.25 x .375 wall DOM has a bending FS factor of 1.94, but would have a buckling factor of over 10.

[Lars]

Great insight Lars. So when you say a FS factor of 2 is recommened, are you talking about the bend FS factor or the buckling FS factor? According to Highlander, the 2.25 x .375 wall DOM has a bending FS factor of 1.92, but has a buckling factor of over 10.

I was thinking bending, not buckling. One thing I should clarify is that the FS you shoot for depends on the application. In other words, how the component gets loaded, and how likely it is to be loaded beyond static conditions. It can get into the realm of grey area, and be fodder for a good argument, especially if is involved.