4 link for dummies

[crawlin68]

I thought that it would be a good idea for an official "4 link for dummies" thread. It seems that you can't go on any other boards and ask the basic questions about how to build a 4 link without getting blasted. So.....this is the thread for dummies. Feel free to ask any question without the fear of being flamed. For those of you that are in the middle of doing this or have done this, this is your chance to help the rest of us get up to speed on this subject. Please feel free to share your knowledge and wisdom.

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!

[highlander]

I thought I would put this link here for those who missed our discussions the first time around:
http://www.norcalbroncos.com/forum/s...ead.php?t=1558

[crawlin68]

Originally Posted by highlander

I thought I would put this link here for those who missed our discussions the first time around:
http://www.norcalbroncos.com/forum/s...ead.php?t=1558

I agree, that is a great thread with a good discussion about the 4 link and a lot of good pictures if you already know what all of the basic terminology and parts are, but it glossed over all of the basics and went right into the design phase. I'm hoping that this thread can start with the basics and go from there.

[highlander]

Quote:

Originally Posted by highlander
Well maybe I should be thinking 3/8" for the lowers. I will go in on a 20' stick of 3/8" DOM. And for your uppers if you don't mind the extra beef you can use the 6' of 1/4" wall that I don't use. I wouldn't mind having some extra 3/8" for a spare link.



Originally Posted by Crawlin68
Yeah that sounds good. We can get the 20' stick of 2 inch 3/8 (what is that, .380?) wall from Valley Iron. What OD is your .250 wall DOM?

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.

[highlander]

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

[crawlin68]

Originally Posted by highlander

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

Yes, it is available. If you need a 1.5 ID, then we'll need to step up to the 2.25 x .375 wall. That's fine with me, bigger is better for Mr. Overkill. So how much of the 2 x .250 wall upper link DOM do you have?

[720Racer]

Originally Posted by crawlin68

Yes, it is available. If you need a 1.5 ID, then we'll need to step up to the 2.5 x .375 wall. That's fine with me, bigger is better for Mr. Overkill.

2.25" OD, .375 wall = 1.5" ID

[crawlin68]

Originally Posted by highlander

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.

[5150bronco]

Originally Posted by crawlin68

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.

How much total length of tube will I need to do a front and rear 4 link?

thanks!

[720Racer]

.....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. And Lars was comfortable making is new Radius arms w/ .250 wall.

The text (attachment w/ the 4 link calculator) says to shoot for a FS of 5 to 10.

Originally Posted by 4 Link Calculator text attachment

A F.S. of one (1) would mean that if all calculations are done correctly that the links shouldn't fail. However, because of the assumptions made a number higher than 1 should be sought after. If you want a ballpark number try to shoot for 5-10 for everything except bending which you should just try to get in the 1-1.5 range.

I believe the Cage/JD arms are 2" OD, .313 wall.

Originally Posted by Cage Offroad

We use 1/4" steel plate combined with 2" x .313" wall tubing.

[highlander]

Thanks Galen, sounds like the .250 gets us in there recommended range for bending, but if the .375 is available I would rather go that route.

[highlander]

Yes, it is available. If you need a 1.5 ID, then we'll need to step up to the 2.5 x .375 wall. That's fine with me, bigger is better for Mr. Overkill. So how much of the 2 x .250 wall upper link DOM do you have?

I have two 3' lengths and one 6' length (I went an measured I thought it was 8'). The 2" x .250 is available in Fresno (Trail Gear) for $1.82 per inch in any length, kind of high. Poly Performence has it at $1.25 an inch plus shipping. But, I am willing to give you some of the tube I have in partial trade for my part of the 2.25" x .375 wall.

[Lars]

Originally Posted by highlander

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.

[crawlin68]

Originally Posted by Lars

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.