I am going to do a 4-link suspension in the front and rear of my Bronco. But I am trying to get educated first. What is the concept of 4-link and how does one do it right the first time.

I noticed several different set up’s in the past year and heard complaints from several people regarding travel.

What would I need to look out for, how do I build one, and what should I build it out of?

How much harder is it to do in the front then the rear?

Dave Berryman

here's a link to the famed god of suspension thread. a link suspension takes a good bit of engineering and if done poorly can be a serious safety hazard. Make sure you completely understand everything involved before undertaking such a project.

http://www.pirate4x4.com/forum/showthread.php?s=&threadid=7503&highlight=god

-Steve

Well now I have even more questions, (BTW, thanks for the thread).

Anti-squat...I understand this to be when you get on the gas hard the axle will actually move in a forward arch toward the front while pushing the vehicle upwards but the vehicle is not keeping up with the rear axle right? This causes it to hope and break traction, right? So how does one fix this problem? I really didn't see any good answers on that thread.

I guess this next one kind of answers the last question but raises another...Link Angle. If I properly set this up I want the link angle to be almost parallel with the chasie (sp?), right? If I do that then the Anti-squat is decreased? But what happens to travel when this is done?

How do I determine CG? And how does this tie into the big picture?

Rear steer and Roll Axes...what is rear steer and what is Roll Axes?

So this is the first step huh? Cool!

Dave Berryman

Do you know anything about vector geometries? I only know about *yea* much, so my apologies for the poor explanation. But if you have an angled link, the compression force on that link (as the vehicle accelerates) translates into a horizontal and a vertical force. You can use trig to calculate exactly what those forces are.

But since it's a system of links, the forces on one link might be negated by those of other links.

Rear steer is a (somewhat) unintended byproduct of the suspension design. As the truck articulates, the drooping tire will travel forward in relation to the vehicle, while the stuffed tire will remain in the same position or possibly even travel rearwards. This results in the rear axle being turned in relation to the truck, and "steering" toward the stuffed side of the truck.

Again, depending on the location and angle of the links, you can minimize the amount of twisting. It's all just a tradeoff one way or another.

Anyway... I'm still wondering where this idea came from. No offense Dave, but isn't this a case of "if you have to ask, you probably can't build it?" I mean, what's the underlying motivation here? Because somebody told you link suspensions are cool? :flipoff2:

I really think you can get more articulation than you need in that Bronco with a lot less $$ and engineering than a true tube link suspension.

I have an uncanny ability to look at something after it has been explained to me and see how things work. Not sure where I get this from but it's been a gift that has helped me in the past.

The real motivation here is to better articulate the Bronco. I know that if I talk to 10 different people I would get 10 different ideas...so with that in mind I have done some checking around and this happens to be the way I decided to go with.:D

As far as funds go that is not an issue. I know that I can do it cheaper and even maybe as good but I am really hoping to compete in a year or two after learning the limitations of my Bronco.

OK, now back to your first question Sclemons...I know nothing about vector geometries:( But after reading more and thinking about it logically anti-squat makes since to me. But my question here is do I need to make the links parallel to the frame to keep this at a minimum?

Thanks for explaining rear steer. That also makes since if you just think about it for a second. How would I build this to keep that at a minimum?

As far as if I had to ask then I prob shouldn't build it...well if I had that attitude I wouldn't currently own a multi-million dollar business :D

In order for me to build a performance truck that would do ok on the streets I need to ask questions, learn the right way to do things, and then go at it. My chances of success are greater then. At least I am willing to learn. Some people think that they know it all and are hard to deal with. In my business if I had that attitude then I would be small still.

Dave Berryman

You say compete, but what type of comp? Rocks, mud, CORR, SCORE, what? That plays a big part in determining what you're doing, too.

Keep in mind that radius arms are a link suspension. A good radius arm susp is easier to engineer (IMHO) than a full-on five link.

And yes, having the lower links close to parallel with the frame can decrease antisquat. But as I said before, it's a sum of all the links. If your upper links run from a relatively low point to a point high above the pumpkin, they can negate some of the lift forces even if the lower links have a substantial angle designed into them.

You realize that getting better articulation in the rear is going to mean hacking out the wheel tubs and a good bit of the bed, right? The tires have to have somewhere to go.

The bottom line is that you should build your truck in a way that makes sense. And you tend not to make a whole lot of sense when you talk about building something up. It's nothing personal. :D

And to answer your question about rear steer, I saw a rig a while back that had both upper and lower links angled toward the center. The lower (IIRC) links went from close to center at the frame to the outer edges of the axles / \ while the upper links went from far out on the frame to the top of the diff \/

I dunno how well it worked in action, but it should help. Limiting the droop with straps will also help, but I guess that gets in the way of the insane flex you're after. :flipoff2:

BTW -- Talk to Chris S on TrailTech about that Jeep a buddy of his built way-back-when.

Shawn is absolutely correct in that there is major information missing here. No one can give you help unless we know exactly what you plan on doing with it. Whatever you do don't got to the general 4x4 forum and ask "how do I build a good 4 link". We'll eat you alive. That's the way and the manorism of this list. There is a lot of reading on this list. You can find more information than you ever thought possible. Do searches on things like: Suspension design, 3 link, 4 link, rear steer, anti squat. This is one I like:
http://www.pirate4x4.com/forum/showthread.php?s=&threadid=7153&perpage=39&pagenumber=1
Don't forget to follow any links that other people mention in the article. There was a great discussion on DesertToys rig.
It's very hard to answer the question: What suspension is best for me.
You need to have something in mind and say will this work, why or why not. On this board the common answer to the question you asked is "Do a fawking search Newbie :flipoff2: "
I think you've got some good fuel now, so go to work and come back in a couple of days with more specifics.:beer:

"If your upper links run from a relatively low point to a point high above the pumpkin, they can negate some of the lift forces even if the lower links have a substantial angle designed into them. "

I was thinking about that...and with out having some pictures in front of me to help the thing I was thinking of was to have the links both upper and lower parallel to the frame , so that would mean the axle would need to be in that parallel line right? Another question I had was do both upper and lower links need to be the same length to help with droop? That would make since. If not then the shorter (presumably the upper ones) would be the limiting factor right?

"You realize that getting better articulation in the rear is going to mean hacking out the wheel tubs and a good bit of the bed, right? The tires have to have somewhere to go."

Oh yeah, I have plans to hack and fab new fender wells and some other "cool" things, lol.

"And to answer your question about rear steer, I saw a rig a while back that had both upper and lower links angled toward the center. The lower (IIRC) links went from close to center at the frame to the outer edges of the axles / \ while the upper links went from far out on the frame to the top of the diff \/ "

I was wondering about the \/ and /\ thing. This is what I saw in some of the designs out there. I take it from you remarks that the \/ or /\ is to keep rear steer to a minimum, but how does this work?

"BTW -- Talk to Chris S on TrailTech about that Jeep a buddy of his built way-back-when.

Ok I will talk to Chris thanks.

Dave Berryman

Hey Dave, you have a couple of ~10-14 yo kids, right? Do they have any of those Technics Legos?

It might sound dumb, but you should be able to build a pretty decent Lego mockup of the links and an axle that will let you play around and see what different link arrangements do to the axle motion.

Keep in mind that the link placement also determines the pinion angle. You don't want to position the links in such a way that the DS binds at the pinion yoke.

In a heim-and-tubes link suspension, you don't need to worry much about limiting droop. The heims move freely along one axis, so your concern about the length of the links should relate more to the overall motion of the axle (droop, stuff, and twisted) rather than to what will give "more" droop.

Shawn
who still thinks you'd be perfectly well off with some custom leaves and some tweaking... but what do I know?

Originally posted by sclemons

Shawn
who still thinks you'd be perfectly well off with some custom leaves and some tweaking... but what do I know?

What DO you know? :flipoff2: I know you're in the fawking stoneage. And don't give me crap about 1 or 2 competitors using leafs. Well off is totally different from leading the pack.

Thanks broncorob for that link. It was very useful.

As I understand some of the threads to say is that if a 4 link is done in the \/ /\ fashion and the upper/lower links are parallel to each other and the angle from the chase (sp?) to the axle is not extreme at all then this would be optimal cause there would be a little squat which is helpful and the rear steer would be minimized due to the \/ /\ design.

Shawn I love your idea of the Lego thing. This definitely would help and I bet I could come up with some pretty close to scale ideas.

The pinion angle is something that I thought I would need to be worried about. When building this would I want to rotate the axle so that it is in line with the t-case? I don't really plan on having much of a lift. Maybe 6" or smaller. Instead I plan on tubing and cutting. I want to keep the Bronco from getting top heavy. I will prob be running 38' or 39's.

How do I determine the CG and how does this relate to the overall design?

Dave Berryman

Originally posted by broncorob


What DO you know? :flipoff2: I know you're in the fawking stoneage. And don't give me crap about 1 or 2 competitors using leafs. Well off is totally different from leading the pack.

Oh... I'm sorry. I must have missed those coil-overs sticking up through the bed in the back of your truck. :D

Oh... I'm sorry. I must have missed those coil-overs sticking up through the bed in the back of your truck.

Soon my friend, soon!
Nah, realistically I'm not sure what I'm gonna do with the rear yet. I have been doing some photochopping tho :D
I've got lots of ideas spinning around :bounce2:

Dave, you have got alot of homework to do. You've got a good start. Basically these ideas are sound. Putting them to work becomes a different story with lengths and space restrictions. If you have a CV driveshaft then the pinion should point directly at the Tcase yoke. If no CV then the angle of the tcase yoke and pinion should be equal and opposite.

Shawn has a good idea but you should build a real scale model. If you've got the skills to build this suspension then you can build a scale out of small tubes and see just how everything works. This way you can find the best lengths of links, angles, and mounting positions. Figure it out now before you get into the realy thing

"If you have a CV drive shaft then the pinion should point directly at the T-case yoke. If no CV then the angle of the t-case yoke and pinion should be equal and opposite. "

Broncorob, is it better to have a divorced t-case in this instance? Kind of the "lower the engine and tranny" theory.

There were many opinions on weather to put the links on top of the axle or have the lowers connected to the centerline of the axle and the uppers connected to the topside, which argument makes the most sense?

As for real scale models out here in Minnesota we are limited in the hobby shop area. I'm not sure I would be able to get my hands on good stuff to work with, but I'll look.

Dave Berryman

Originally posted by mrb

As for real scale models out here in Minnesota we are limited in the hobby shop area. I'm not sure I would be able to get my hands on good stuff to work with, but I'll look.

Dave Berryman [/B]

I think what he ment by scale model is build a scaled down version of your project (the lego thing) but replicate your rear frame and link system on a small but accurate scale like 1/4" = 1'-0" so you can see what your pinion does as you work the suspention and twist! What I have used in the past is allthread and small heim joints for your links and a 1 1/2" tube for the axel with a flat washer welded to the face as your pinion so you can see all effects of your idea. Hope this makes sence.