Is there anything special to do when setting up a 4-link suspension? Any special way for the setup as far as geometry goes? It seems like they would bind, but I have seen stuff with the bars like this (from top view) l/\l
that way the center links triangulate teh set up to prevent side to side sway.
How doyou account for binding and avoid it?

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your best bet is to just play around with it some. trial and error is the way most everyone gets it right....rarely is it on the first try. your idea is right though. also math/geometry plays a big role.... if you are a lil rusty on old high skool math borrow a book from a library and touch up on it. i know i had when i was designing a 4 link for my truck.

now for the technical stuff... the two most critical factors to the performance of a 4 link suspension are the link lengths designed into the suspension and the angles to which the links are adjusted. upper link angles from 15* to 18* on the right and 10* to 15* on the left provide good forward bite. a good starting point for both links is 15* upwards (to the front). but then you have to take into effect that chassis roll will change then angles and can easily cause everything to go out of whack! If the link angles become more upward on the left than on the right, the left rear tire can become loaded more quickly than the right during acceleration! this may cause a gas pedal push. One fix is to position the links so that the right side link is from 3* to 5* higher than the left when the chassis is at ride height.

BUT... keep in mind that trailing arms angled uphill too steeply can hold the chassis up during acceleration which can reduce the effectiveness of the shocks and springs. this will cause loose handling-especially out on the rocks. Keep in mind that trailing arm angles can become excessive if the rear of the truck lifts a lot during acceleration. although the good news is that you can use the lower links of a 4-link suspension to help offset the loose roll steer tendency caused by the steep angles of the upper links.

that should help get ya started.... i gotta head to class but will post more up later!

-cutts-

 

I think we're stuck with the 'Related Links'. Probably an 'enhancement' that Dennis looked into to cut costs in order to get us more stuff. Growing pains...either the annual dues go up, or we deal with the 'Related Links'.
Oh, and about cutts' explanation...
huh?
I think I'll just stick with my trusty old leaf springs and add the coils for bling factor...

 

Raw, I've read a lot of books and junk on link angles and will tell you that there seems to be no universal formula. What works in some rigs doesn't work in others. Limiting straps will go a long way to saving parts when you're experimenting with it. 2 big things though, and not everyone follows this but it's proven and tested in monster trucks so I figure it must be good for something. Make your upper and lower links the exact same length as each other . . . as in you could chop all 4 link bars to the exact same length. The other thing is if you view your links from the side the distance between them (upper and lower) should remain the same all the way. You'll want them spaced the same distance at the axle as they are at the frame. If you do both of these things you'll get good smooth suspension travel and your pinion angle will remain consistent as the suspension cycles. Then the only thing you need to toy with is the total length of the links which in turn will determine their final angle. Fishy posted some general figures but this can vary a lot depending on the weight of the rig and the distribution of weight as well.

Last thing, but you probably know this, ideally you're going to want the upper and lower mounts directly above and below the axle. So if you drew a line through the centers of them it would cut right through the middle of the axle tube. A lot of guys get fancy and shift the lower links forward and up to improve ground clearance (rock crawlers). It can be done but it complicates things a bit and isn't necessary for most applications.

Btw, I know it looks like it will bind . . . it won't, trust me. If I can get some parts together Pro and I are going to tear into the back of my trail rig in a few weeks here and 4 link it. Right now it doesn't have a tranny so I won't be able to test it out for a while. Surprisingly the BIG expense with 4 link suspension is the heim joints. I priced out 1" heims for front and rear 4 link for my truck: $900 Soooo I need to get a few $$ together and just start with the rear. I'll do the front later on.

 

HOLY CRAP SNACKERS BATMAN!!!!!! are you serious?? thats crazy............well, i guess they are the most important part of the system.....BTW ivan, what are you thinking about using for link arms, what would hold up the best and not snap like a toothpick??

 

Okay, that right there was funny. Actually, its about what I said too. I knew it was gonna be spendy but not THAT spendy.

Some people use pipe for their links, but personally I'd stick with dom, especially on our heavier rigs.

 

I'm going to start with schedule 80 pipe on the trail rig for my links. I'll eventually go to DOM but at $10+ per foot it's a little too pricey to use for experimenting. Once I get a working system and I'm happy with all the angles and link lengths I'll switch to DOM, probably .25 wall.

FWIW White Knight still runs poop pipe, I think schedule 80, for their links. It's not as strong as DOM but it holds up fine to all their abuse in terms of jumps and that mess. Pro and I were laughing (almost in horror) when we watched their video. They don't rock crawl, they rock jump. Theresa and Robin have a bit of a heavy foot and they hit the rock pit full throttle and TOASTED their joints. They were bent completely but they kept on going. DOM would have bent just as bad but cost 5X as much to replace.

 

Thanks for all the info. I may just stick with ladder bars as to not complicate things.
Im not that rusty on Geometry, just got out of it last year (yeah Im in highschool)...

 

Does 4-linking alloy full articulation or will it bind when the axle is off camber? It seems to me that it would be some what restrictive for rock crawling and such.

 

Ideally, they're designed to articulate beyond usable, to degress that wouldn't even warrant driveable because of driveshaft binding. For example, a well-designed 4 link would allow you to pick the truck up by the frame to about 5 feet off the ground, and the rear axle (with no shocks, limiting straps, or driveshaft) should be able to swing down a good amount without binding, in almost a perfect arc. If articulation isn't really needed (in a mud truck, for exampe), then the precision doesn't really need to be THAT we thought out, but it still shouldn't bind through the length of the limiting strap. The limiting strap is usually a 1-2' long piece of heavy chain or tow strad attached to the axle and frame which keeps the axle from articulating beyond the limit of the shocks.

 

Ditto. You'd need a hell of a CV joint AND one hell of a slip joint.

 

Hey! Is that one of those 'MONSTER TRUCKS!' I saw on EBay, that all it needs is a front driveshaft, and drives great down the highway, and gets lots of looks?

 

Bwahaha! Nope, that's Evolution just testing out their 4 link design. Those are the guys I'm buying my heims from. They actually construct their own. If you want to see some of his trucks in action buy White Knight's videos. He's building some of the baddest suspensions around.

 

I agree. Those pics are AWESOME. I downloaded most of the White Knight video clips and run them on my computer pretty frequently. It's good to see someone USING the suspension and the truck or 'truggy' it's attached to. That sounds kinda dumb coming from someone with a full-on mall crawler, don't it?

Cody