I'm in the planning stages of the 4-link of my rear end. What I'd like to do for ideal placement is to put the outside links even with the outside of the frame and on top of the axle tube. For the upper links I'd like to put them on top of the diff and at the top of the frame.

Am I going to have problems with axle wrap if I do this? If I put the ouside links on the side or bottom of the axle tube I'll have to put the uppers on the bottom of the frame and that would give me problems with hanging up on things

-Jack

I heard a good rule of thumb is to make the lowers and uppers at least 6" away from each other, vertically. This assures that wrap will be adequately controlled.

What vehicle, powertrain, tires, etc??

Built 302, 435, soon to have a cold duck (dual 20's), 9" and 38's.

-Jack

with that power and tire size i would be concerned about your instant center as well. Without looking at it, it's hard to say, but you may want to consider lowering the frame mounts for the upper links. This will help lower your IC, it sounds like your lower links will already be as flat as they can go.

edit: search back and read the thread about anti-squat as a percentage, and the other one about 200% anti-squat. Those are both good threads

Originally posted by elf_cruiser
edit: search back and read the thread about anti-squat as a percentage, and the other one about 200% anti-squat. Those are both good threads

Yeah, read those
200% Anti-squat thread (http://www.pirate4x4.com/forum/showthread.php?s=&threadid=72252&highlight=antisquat)
Anti-squat percentage thread (http://www.pirate4x4.com/forum/showthread.php?s=&threadid=70358&highlight=antisquat)

You know, I read through both of those god damned things and it's tough to figure out. Especiallywith everybody contradicting everybody.

So here's my plan, in a nutshell, summed up so all can read and understand without trying to play it up with a lot of engineer speak.

I'm told that with EB's the center of gravity is around the rear of the crank. So I'm going to point my links to it. At the same time I'll be moving the rear end back about 6". The links will be around 35 to 40" long.

As for the upper link, I think I'm going to move it up a bit on the diff side. I'll put a gusset along the top of the axle and put the link on top of it which will move it up about 2" or so. I'll have to measure if it is 6" or not from the top links. I may have to put them in the front of the axle instead of on top.

So here's my question... WTF, in plain english, is the instant center and what should my goal be? Should it be to keep the links parallel, to keep them level with the ground or ? In English please!

Originally posted by IronBenderII
As for the upper link, I think I'm going to move it up a bit on the diff side. I'll put a gusset along the top of the axle and put the link on top of it which will move it up about 2" or so. I'll have to measure if it is 6" or not from the top links. I may have to put them in the front of the axle instead of on top.

So here's my question... WTF, in plain english, is the instant center and what should my goal be? Should it be to keep the links parallel, to keep them level with the ground or ? In English please!

Take a picture of your rig from the side.
In photo shop make it black and white and basically strip everything out of it Including the tires but leave the wheel centers and contact patches for a baseline.
Make sure the contact patches are level or you will fuck this up.

Print it and make multiple copies.

This is your little planning doodle pic, take it with you when you go to the bar. :beer: = good, except when you are actually building it.


Now draw in your UCA mounts at the axle and chassis.
Draw in your LCA mounts at the axle and chassis.
Draw in the COG
Draw a line from the center of the bolt on each mount of the LCAs and continue that line of both ends of the paper.
Do the same for the UCAs

Where the 2 lines you just drew intersect is your "instant center", it's relationship vertically to the COG determines how much anti-squat your links have.


EDIT: If you move the axle mount higher you will be lowering the instant center, that help ya some?

Dude you rock.

So you want your instant center to point to your center of gravity. This is to help manage anti-squat, right? So what I've been thinking (over beers) is putting a bracket on the lower mount with 3 mounting positions. This will give me a bit of tuning ability.

Now, since you seem to have a great handle on putting things into English, what about rear steer. Is it BASICALLY the longer the links are, and the more level they are to the ground, the less there will be?

Finally, I'm curious about roll centers. As I understand it, if you don't have it right, you will tip over in the parking lot. What is the ideal configuration? Again, if you could put it into English, that would be very helpful.

THANKS AGAIN!!!!!!!!

-Jack

Originally posted by IronBenderII
Now, since you seem to have a great handle on putting things into English, what about rear steer. Is it BASICALLY the longer the links are, and the more level they are to the ground, the less there will be?

Finally, I'm curious about roll centers. As I understand it, if you don't have it right, you will tip over in the parking lot. What is the ideal configuration? Again, if you could put it into English, that would be very helpful.

THANKS AGAIN!!!!!!!!

-Jack

Rear steer, the longer the links the better. The more leval to the ground the better, for anti-squat as well.

Roll center, you want that as high as possible, or you will tip over in the parking lot. The higher the roll center, the more stable your rig will be in turns

How do you determine (in English) what your roll center is. And how does that translate to how you want your links. For example, you want where your links would meet from the side view to be as high as possible or low as possible or ?? Thanks guys for the clarification. I'm sure a lot of other people appreciate your help as well.

-Jack

English eh, never was to good at that.

Well, with a wishbone 3-link, the wishbone link pointing rearwards, the axle would pivot of of the single mounting point of the wishbone link, since that link cant move side to side.

With a dual triangulated 4-link, the axle would pivot off of a slight lower point.

Its kinda hard to explain why, mostly because i don't know. But I have built atleast 10 models of these setups at 1/4 scale. The 3-link wishbone upper link works the best as far as I can tell.

I don't know how to actually determine what the roll axis is, just by trial and error with models.

Hope this make some kind of sense.

Can you explain the theory? What is ideal (high, low, left or right)?

Originally posted by jesselt


Rear steer, the longer the links the better. The more leval to the ground the better, for anti-squat as well.

Roll center, you want that as high as possible, or you will tip over in the parking lot. The higher the roll center, the more stable your rig will be in turns


The rear steer comment is wrong for the most part. As for antisquat, you want a little of it. Look at the antisquat threads as stated above. There is good stuff in there. Yes, you want the rol center/roll axis to be as close to the CG plane as possible. This will minimize body roll.

TJ FREAK: good idea dude. bender go do this and post pics, you will get much better feed back. As ELF said it is really hard to help out without seeing any pictures.

Once again here is the diagram IC & RC. (copy + save)
http://www.sierrarockcrawlers.com/data/srcforumuploads/test.gif

Here is kind of a diagram of what should work well.

Dimension 'A' should be atleast 6-8", maybe more with your 302

Dimension 'B' should be as little as possible.

Dimension 'C' and 'D' should be as long as possible.

The links should also be a close to parellel to the ground as possible.

The upper link mount on the axle housing should be as high as possible.

Originally posted by PIG
The rear steer comment is wrong for the most part.

Why is that, care to explain your theory on this one. I'd like to here it. I know the links also need be close to parellel as well, that makes a big difference to, but if the links are short, there will be problems with rear steer.

Originally posted by jesselt


Why is that, care to explain your theory on this one. I'd like to here it. I know the links also need be close to parellel as well, that makes a big difference to, but if the links are short, there will be problems with rear steer.

OK holms look at the diagram. I am not tryin to flame out here, just tryin to get the facts right. It is very possible to set up a 4 link with short links that won't rear steer. I will post pics when I get a chance.

According to your drawing you will have quite a bit of rear steer. If you want to get rid of it trianglulate the lowers.

PIG's diagram of a rear 4 link cancels out the rear steer. The angled lower links off set the angled uppers, and there is negligible side-to-side movement when flexing...

Sweet thanks, uhhh Mr. Pig (last time I called somebody pig I got a free nights stay care of the county, but that's another story).

Anyway, I was taking a look at a couple of designs and like what Mr. Pig put together. There was one on an XJ and another on Lee's new Bronco (the purple one that the pics were posted of).

So the plan is to build a new cross member at the rear of the transfer case (will also act as one side of the skid plate). Then put the upper links pointing out and the lower links pointed in. I'll keep all of the links equal length and keep them all at the same angle (when looking from the top).

As for anti-squat, I'm going to point those things right at my rear crank which is right aboutt where my center of gravity is.

You guys are awesome and I really appreciate the help. Next spring when the Bronco re-imerges, the :beer: is on me if I see you on the trail.

-Jack

<---is more knowledgable thanks to this thread. BTT. :D