link suspension opinions... (1 Viewer)

[1978fj40]

hello, first off would like to say, i haven't been on here in a very long time, and thanks to everyone for the info, and my login even still worked. i am grateful!

so to my question: i have a 78 FJ40(in pieces at the moment), i am going to build a link suspension front and rear for it, to attach to rockwell axles. i am debating on using a 4 link using the bracket to attach to the top of the chunk, or doing a 3 link that would have the upper 2 links tie together before attaching to the bracket centered over the chunk. my initial thought is that it would still flex well, and hold the axle centered without a trac bar. has anyone done this? if so, does it work well? i have 1.25 inch heim joints with high misalignment spacers i bought a few years back when i started this project...

 

[nckrsamford]

i am doing the same project right now, but i am almost finished. I went through 3 different link set ups for the front and rear. the best set up I came up with was four link front and rear. my stance is higher because i didnt move my engine back. are you going to run pinnion brakes, because if you are you need a total of 3 to 4 inches (depending on which rotor you go with) above your third member in the front. are you going to back halve your cruiser? I put my rocks under it when it was stock length and found out that i had to back halve it, because I could not get the link travel that I needed with that short of a wheel base. the four link that i went with in the rear was two uppers to the top of the pumpkin, and the two lowers to the inside of the hubs, ie... i v i - which is a single triangulated four link. I did the same in the front but reversed it, which is lowers to the center of the pumpkin and the uppers 10" brackets next to the hubs. are you running stock 2f powertrain? is it rear stear? if so you might have to turn the rear third member chunk and reverse the pinnion, depending what side your transfer case drop is. I dont have alot of pics on my build up but you can get an idea from what I have on there, it is called " the hobby my wife hates" and its in hard core build ups. By the way I flexed my cruiser today with out the wheels on just to make sure nothing bound up with my coilovers, links, etc... and my driver hub was 5ft in the air with my back axle flat on the ground and I still had 6in of travel in the front shock and 8in in the rear left, and my engine jack wouldnt go any farther. so I know this set up works.

 

[LC_Hamma]

Triangulating links under the oilpan will force you raise your ride height alot for clearance. If you can pull the front axle forward, that'll allow the chunk to articulate just below the radiator & frame crossmember. Your upper links will be short depending on location of the frame mounts. Set your engine in there & check clearance if your running headers & where your motor mounts are. For the lowers, build your crossmember & tie an easy to remove skid plate to it. What's the rest of the drivetrain consist of?

 

[1978fj40]

thanks for the info, do you have to run a trac bar to keep the axle from walking side to side, or will the links hold it in line? i am planning on running pinion brakes and have been warned of the clearance for them, i am planning on building tall, so it should not be a great issue. i am going to stretch it as much as possible, going to try to put front axle where chunk will be under radiator area. i am planning on using coil springs instead of coilovers, and would like to trim the body on the back just below where the hardtop sits on, so that i can still use it in bad weather mostly..

my powertrain is a chevy 350, sm465 trans mated to a np205 t-case, RH drop front driveline.

i am not doing rear steer

 

[mookie]

i'd avoid the 3 link, imo puts too much stress on that one top link....if it lets go your axle spins around and trashes your shocks and d-shaft.....seen it happen twice and it ain't pretty

 

[Mace]

i'd avoid the 3 link, imo puts too much stress on that one top link....if it lets go your axle spins around and trashes your shocks and d-shaft.....seen it happen twice and it ain't pretty

if one of the 4 links lets go you have pretty much the same issue..

The key is to build strong.

 

[nckrsamford]

mase, I am not trying to be mean, but have you ever done a link set up? It is not the same if a four link breaks one of the links. if that happens then you have a three link setup, tadah! There is a thing called vertical seperation that keeps the axle from turning which is called axle wrap. if one link breaks in a four link you still ok, now you wont be able to wheel hard but you can make it back to the camp. When ever you do a link set up you have to have some sort of vertical seperation for the set up or you just turned everything into crap.

 

[Mace]

mase, I am not trying to be mean, but have you ever done a link set up? It is not the same if a four link breaks one of the links. if that happens then you have a three link setup, tadah! There is a thing called vertical seperation that keeps the axle from turning which is called axle wrap. if one link breaks in a four link you still ok, now you wont be able to wheel hard but you can make it back to the camp. When ever you do a link set up you have to have some sort of vertical seperation for the set up or you just turned everything into crap.

Awesome, you sure about that cowboy??

Go remove one of your 4 links and drive it around. Report back.

 

[nckrsamford]

pretty sure about that, before I put the fourth link on i articulated it to full articulation to check for binding because of the placement of the chassis side link mount and it didnt falter. moved it side to side and it didnt want to fall at all. do the math Cowboy and the geometry and then get back with me.

 

[1978fj40]

thanks for the input guys. looks like i am gonna do a 4 link on it, it seems to be the most liked, and it is what i originally planned on. has anyone run coil springs instead of coilovers? how well do they work? where is the best place to mount them? build towers outside the frame? thanks again for the help

 

[LC_Hamma]

I run coils on both my rigs. The 40 rides awesome & the isn't quite ready yet but I predict more awesomeness ;p Those are both softcore rigs anyway. I scavenged coil buckets from a TJ. Plan on running sway bars since you are building "high". I'd mount the coils outside the frame for sure. Are you tubing out the rear? The rear coils may be too close to your tires so you may need to chop the frame. Plan on, at least, 6" lift coils. I assume you'll be running 44's or larger?

 

[Mace]

pretty sure about that, before I put the fourth link on i articulated it to full articulation to check for binding because of the placement of the chassis side link mount and it didnt falter. moved it side to side and it didnt want to fall at all. do the math Cowboy and the geometry and then get back with me.

So, go drive it a bit with an upper removed then..

How am I supposed to do the math on your setup? The reason it did not move much while on jackstands is because the bushings that you used on the lower frame side will do a pretty good job of keeping it steady. if you drove it without a link, the axle would walk all over the place and in the process move the pinion up and down.

Is the front end done yet? Or even started?


For what it is worth to the OP,
If you can do a doubly triangulated 4 link in the rear you will be the happiest. The three link you are talking about is called a wishbone three link. It can be a VERY strong setup and works very well. Take a gander at some of the Twisted Customs rigs for good examples. The problem with a wishbone three link is that you can end up with a significant amount of rear steer.

Front suspension is hard to do a 4 link on without making it really tall. And, if you are not running full hydro, a significant amount of bump steer is common (not impossible, but common)

A true three link with a panhard works well if you are still going to use a steering box. Make the PH bar the same length as the DL and parallel. If you are running full hydro, then all bets are off.

Upper links are generally in tension, so they do not have to be quite as stout as the lower links in compression. You are obviously need to put the axle in and see exactly where the axle will end up before making any hardcore decisions.

Get the 3 and 4 link calculator and measure what you CAN do before you decide what you have to do. Obviously, removing the front and rear tub/frame helps considerably.

Work it out on paper before you fully decide what you want to do. There is no single link system that fits every vehicle.

 

[1978fj40]

i am planning on running full hydro steer, i think that a single triangulated four link on both ends is what i will aim for. i am planning on building drop brackets off of the frame to mount the suspension to, so i *should* be able to achieve this, however, still in research stage trying to make sure i don't hate it when done.

LC_Hamma

i was planning on running the 6" jeep lift coils, since everywhere has them mostly, and the TJ is about the same size vehicle. would you suggest the TJ 6 spring of the XJ 6.5 spring, i am about the same size as a TJ, but much heavier, which leans me towards the XJ spring..

just to explain my "building tall" i want to run the military 52" michelin tires. i know they won't grip real well, as i have read, but for the price, i am gonna try them. but i really don't want to backhalf this thing... i would ideally just like to trim the tub just below where the top goes on. i am overbuilding the amount of flex this thing will have for what i do, but don't want to have to re-do my suspension later if i change directions with what i use it for...

i agree sway bars could be a good idea, it may get interesting without them

 

[LC_Hamma]

With 52's, I'd backhalf the rig. You won't have *any uptravel if you wanna keep the tires under the wheelwells. Look at some of the Proffitts rigs, they run 44's+ & are all tubed rears. Then again, I don't know how high you are jacking this rig up, maybe a monster body lift? Have you mocked the tires in there yet? Those 52's on an FJ40 will look kinda Post up some pics already ;p

 

[1978fj40]

i agree it is going to look kinda funny, kinda like an rc car i would imagine. i don't have any pics currently, can't find the old ones, and no use taking a pic of a tub sitting on stands, or frame on stands really. if i have to backhalf i suppose i will, i would just rather not. i am planning on getting the shop cleaned out a bit and beginning to look at some mock up this weekend, so that will probably give me a better idea of what is necessary. i do beleive that you are correct however, with 52's i will have little up travel in the rear, i have contemplated the body lift, but they look like crap. i put one on my other truck, and am still undecided if it was worth it. my original thought was that since i do mostly river driving (loose sand and some water) that i would build to accomodate the 52's without being able to use my full flex (maybe only 1/3 to 1/2 of it truly), then if i want to go hit some rocks, i could just swap out for a smaller set of tires and bump stops that would allow the suspension to move more, and lower my center of gravity by quite a bit. does this seem semi-logical? i know it is quite a bit different than most peoples idea of a way to go about it, but i *think* it will work out, however, that is why i am here, to see if anyone else thinks that it will...

 

[BellyDoc]

I've "done the math". Mace is dead on.

If the "4-link-minus-1" were a stable situation and safe to drive, then a 3-link suspension wouldn't require a panhard bar.

If you think about it for a second, it's obvious why this is the case.

First, consider the triangle created by the lower links and the axle. If there were no upper links, this triangle could pivot side to side in an arc, rotating around the point where the lowers meet on the chassis. If the links are separated a bit at the chassis, there is still free side-to-side swing, but the axle "parallelograms" a little with side to side motion, too.

Second, consider the upper links. The triangulated uppers serve TWO purposes. They prohibit axle wrap AND they also prohibit side-to-side motion. If there's only ONE upper, then the axle could swing side to side as long as that motion were coupled with "wrap" or "anti-wrap" at the same time.

If you really want to see this freely, put your XX rear ended rig up on a hoist and let the rear end dangle so that the axle hangs from the coilovers or limit straps... or else use some chain. Then, remove one upper link.

Now, cowboy up and give the axle a real shove side-to-side. Use a come-along if you have to.

If the axle swings AWAY from the attached upper, then that upper will pull, and the axle will "anti-wrap" with the pinion dropping. If the axle swings TOWARD the attached upper, then that link will push, and the housing will "wrap" with the pinion angle rising.

If you tested yours, but you didn't notice this result, there could be a variety of reasons.

It could be because you were applying the wrong sized forces. More oomph would then have done it.

If you've got bushings instead of rod ends on the chassis side, you might have had enough spring in the material to resist a moderate movement.

If you have rod ends, and your axle was on jack stands, then the friction of metal on metal might have lied to you.

If you had the wheels on the axle and the axle on the ground, then it simply doesn't "shove" side to side, and you'd notice something completely different when in motion.

The amount of force created by a vehicle under power is MUCH MUCH more than you'd typically be able to apply without hydraulic tools. That's why moving parts that seem to float freely on a vehicle are often too tight to move by hand. Face it... we're ridiculously wimpy compared to what happens when you put a gear box on the end of a V8 and then stack a couple of tons of metal on top.

Please... DON'T do what Mace suggests, though... it's NOT WORTH IT. You would probably accelerate slightly, your axle would wrap and walk toward the side with the attached link, your rear pinion U-joint would instantly max and then SNAP!!!! You'd have killed a perfectly good drive shaft.

 

[Mace]

Please... DON'T do what Mace suggests, though... it's NOT WORTH IT. You would probably accelerate slightly, your axle would wrap and walk toward the side with the attached link, your rear pinion U-joint would instantly max and then SNAP!!!! You'd have killed a perfectly good drive shaft.

Killjoy..

 

[BellyDoc]

Oh... and although I have nothing to add to help out in terms of working with the Rockwells, I can tell you that if you really want to triangulate the front uppers (and you should) then you're going to end up stretching the front forward so that the links can wrap around the sump. Mine had to clear around my exhaust system too, which also wraps around the sump.

If you don't, you'll end up with an unnecessarily high CoG.

I couldn't bring myself to build a rock magnet crossmember under the drive shaft for the lowers. It would have either been quite far back making the links too long, or quite low and ruining flat belly ground clearance. Alternately, I could have gone to a two piece front drive shaft and flexed it forward of the link mounts, but then I'd have had to anchor up a pillow block... and that seemed like a major cluster-F to deal with.

The front end here is a high pinion D60, driver's side pumpkin:

As you can see, the axle tube is basically right under the radiator.

I'm not saying that I know this design works. What I've got at this point is a 2 ton paperweight on wheels.

However, it's a fairly well considered paperweight.

 

[Mace]

Belly, that all buggy? or partially cruiser?
Looks good
Looks all buggy.
MUCH easier to design a suspension without a existing frame.

 

[BellyDoc]

Killjoy..

Relax... I'll make it up to you... we can grab a 12 pack and some lawn chairs and go hang out at the Golden Gate Bridge, chanting "Jump! Jump! Jump!"