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.

[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.

[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?

[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.

[720Racer]

.....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!

What I've learned so far (I'm only scraping the surface);

COG, a crude estimation is the height of the cam @ the bell housing.
Anti squat, weight being transfered to the rear axle upon acceleration, 75% to 85% for off road vechiles that will/may be driven on road, more for desert racing (Lars).
Roll center, the (theoritical) point (described as a height off the ground) the axle articuates on.
Roll axis, negitave or positive number of degrees of the roll center, the sensation that the vechile is leaning into the corner or out of the corner (read up hill or down hill while on a side hill) when power is applied.

PLEASE correct what I've got wrong, or add on if I'm missing something.

[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

[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.

[crawlin68]

Originally Posted by 720Racer

2.25" OD, .375 wall = 1.5" ID

Oops, I meant to type 2.25 not 2.5. Thanks for catching that!

[crawlin68]

Originally Posted by highlander

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.

Yeah, Trail Gear is over $21 a foot! That is just a plain rip off. Ballistic Fab sells it $12.90 a foot, plus shipping.


Is 36 inches going to be long enough for each upper once you factor in the 6" for the weld in bungs and JJ's? So that would make a 42" overall link center to center. Is that going to be long enough?

[720Racer]

.....Is 36 inches going to be long enough for each upper once you factor in the 6" for the weld in bungs and JJ's? So that would make a 42" overall link center to center. Is that going to be long enough?

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.

[Delta 4 Wheel]

Originally Posted by 720Racer

What I've learned so far (I'm only scraping the surface);

COG, a crude estimation is the height of the cam @ the bell housing.
Anti squat, weight being transfered to the rear axle upon acceleration, 75% to 85% for off road vechiles that will/may be driven on road, more for desert racing (Lars).
Roll center, the (theoritical) point (described as a height off the ground) the axle articuates on.
Roll axis, negitave or positive number of degrees of the roll center, the sensation that the vechile is leaning into the corner or out of the corner (read up hill or down hill while on a side hill) when power is applied.

PLEASE correct what I've got wrong, or add on if I'm missing something.

Muchos Gracias...