Four link and leaves?

[Beezil]

check out those por threads.

man, you'll have more questions than answers reading those bad boys, but that's a good thing!

just take it slow, 4-links can't be rushed. If you wanna see a picture of my set-up, ask jes, or hinkley, or sequoia....I think at least one of them has quite possibly the best angle on it.

 

[MaXJohnson]

How about you build a four link, but use the leafs as the lower links.

Build some triangulated uppers. Remove the solid connection of the axle to the leaf by tossing out the u-bolts and replace with a pivoting joint. Leave the leafs mouted as-is; shackle at the rear, bushing at the front. Your side view geometry will be defined by the front half of the leafs together with the upper arms. Ditto for the plan view geometry.

The pivot at the axle/leaf joint is a variation of Rich's birdcage. The birdcage concept, if used with 4 links and leafs, is perfectly valid for a leaf/link hybrid design as it would de-couple the spring from handling torque under acceleration and braking. That could be hanled by the links, mounted in the traditional manner.

On a dirt car, the links are mounted to the birdcage and another arm is mounted directly to the axle to control torque. The links only handle side view location and a track bar handles lateral location of the axle.

 

[Economos]

How about you build a four link, but use the leafs as the lower links.

Build some triangulated uppers. Remove the solid connection of the axle to the leaf by tossing out the u-bolts and replace with a pivoting joint. Leave the leafs mouted as-is; shackle at the rear, bushing at the front. Your side view geometry will be defined by the front half of the leafs together with the upper arms. Ditto for the plan view geometry.

I once saw a guy with a K5 that did something similar to this. He had only TWO long lower links that tied into the rear housing just inboard of where the leafs were. His leafs utilized the stock frame mounts with a shackle on the rear mount but they were not u-bolted to the housing. I can't remember what kind of joints he used though, probably heims.

Now I really don't know how this thing performed because I never saw it in action. He did drive it on the road quite a bit, but I don't recall what he said about it's mannars. Possibly bootie-fab?

 

[4ward]

Max, you've completely lost me. How are you supposed to keep the axle from flip flopping about? Maybe I'm being dumb cuz it's way early.

CW have you ever heard of the K.I.S.S. principle?

A well thought out and designed 4 link isn't going to work the same with leaves as opposed to every other mode of suspending the vehicle. You would need links in the 25-30" length range to get the arcs working correctly with leaves. That is way too short of a link length to be running anything else and get decent manners out of.

Maybe Ed Stevens will pop in on this one and show us the path to enlightenment.

Greg, a well setup 1/4 ellip/ 4 link can be/ is just as stable as anything else on the road. I think the main key is getting that o so elusive flat roll axis. That's why double triangulation mounted above the axle is soooooo nice. I can't decide if I want a rear sway bar or not. I think they are just a band aid for poor geometry.

Once I get my front axle rebuilt and some non bent wheels and radial tires up front again. I know that doing 70-80 with my junk will feel reasonable again. My limiting factor will be the hydro steer, which is feeling much better now that I've started the pump mods.

Sean

 

[XJJPR]

Oneton,

The birdcage thing is a "jungle" of linkages used in this situation in my opinion. You not only have the 4 link you have links to the axle tube itself to the cage. Talk about a incorrect use of a design for four wheeling in my opinion. The cage is so high maintinance it isn't even funny in it's normal usage where movement isn't that great but in a rock jeep it would be completely rediculious maintinance. The metal to metal movement involved with this set up creates lots of wear in short periods and would be exclerated by the extreme movement of a rock crawler. From all aspects of the design it is used to eliminate axle to frame torque steer. So as power is applied to a race car coming out of the corner the axle isn't transfering unwanted torque to the frame, to then affect the steering of the car.

I'm not sure how all this would translate to a rock crawler, it doesn't make sense to me but then I amit I'm not a suspension or steering linkage designer, I just go drive my junk with the stock style set ups on it.

I'm with you on the short link to match the spring arch, I've done this on a wrangler years ago it work just fine, but wouldn't be adaptable to coils later the links would be to short.

KISS is your best concept here, design for what you're doing/have now and redo it later if you change things.

mark
orgs mfg

 

[Beezil]

besides, when links get as long as 40" like they do in a jeep application, and assuming the person understands the geometry well enough, BINDING IS NOT EVEN AN ISSUE ANYWAY.

 

[4ward]

Better bury your head in those books again B. Bind is inherent in every 4 link. Now a 3 link on the other hand.........

 

[Beezil]

yeah, if its not done right......"assuming the dude understands the geometry" is what I said....

funny, neither you or I have any bind present in our systems, therefore my wording seems accurate.

 

[4ward]

I've got bind, and so do you. Go pop a link out and see what happens.

 

[C-ROK]

Sean, I agree with getting the roll axis low enough to avoid a sway bar, but that's not always easy to do in my opinion.

Due to my wishbone mount location, my rear roll center is very high. The front is fairly low with the radius arm design so I ended up with a descending roll axis towards the front of the vehicle. I have no real sway problems from the front end but did have with the rear. The addition of a small rear sway bar solved all that. My rear sway bar controls the roll quite well and yet still allows full articulation on the trail. Sway bars are used extensively on all kinds of vehicles with substantially less suspension travel than we have. I don't know that I would agree they are a "band-aid" so to speak. I see them as just another suspension component.
I agree that their use can be avoided but often when working within the confines of a pre-defined vehicle structure things like link mount location are fairly well restricted.
You and Beez essentially have a tube frame chassis when it comes to your link mount locations. You need to realize that that option is not available or practical to employee for many people.

What's perfect and what's practical are not always synonymous.

There's a right way, another right way, a few more right ways, some perfect ways, and a lot of wrong ways.
Maybe I don't get passionate enough about pursueing the perfect way

 

[C-ROK]

Re: Heh C-ROK

C-ROK...funny story... I was looking thru the latest issue of FWD&SU magazine and there I saw your pix. Pretty nice too! I was showing it to my secretary with the comment that I knew him from the last Moab trip. She says, "Isn't that the same Jeep that got rollover in the Hot Tub?" I have a 8x10 enlargement of your flip on my office wall. Made a great pix!
P.S. do REALLY like the two hats. Sent one to my son-in-law in Cali.

Hey Dan.
I want an 8x10 enlargement of that photo!!!! Maybe even bigger.
I've got more hats and T-shirts too...... Is there a deal we could swing here????

 

[MaXJohnson]

Max, you've completely lost me. How are you supposed to keep the axle from flip flopping about?

A well thought out and designed 4 link isn't going to work the same with leaves as opposed to every other mode of suspending the vehicle...

I think the main key is getting that o so elusive flat roll axis. That's why double triangulation mounted above the axle is soooooo nice. I can't decide if I want a rear sway bar or not. I think they are just a band aid for poor geometry.

Sean

Dumb? Why are on the computer at 4 in the morning?

Picture a normal 4-link with straight lower arms and triangulated uppers. The uppers locate the axle laterally and upper and lower links locate the axle through the suspension cylce in the side view. Now extend the lower arms past the axle and attach to shackles at the rear of the chassis. Instead of the lowers being built from tubular stock, make them out of flat spring steel. There you have leafs serving as lower links and tubular, triangulated uppers. The only potential problem I can see with this design is if the roll axis defined by the leafs would fight the axis normally defined by 4-link geometry. Other than that, it holds to the K.I.S.S. principle.

The behavior of a well thought out 4-link(not my example) would be independent of the type of spring used. The 4-link design would define the geometry. The spring, whether it's coil, leaf, torsion bar, 1/4 eliptic or what-ever, would only suspend the weight of the chassis and doesn't dictate axle location. The exception to this would be a case where the spring (leafs, as mentioned in my previous post) serve as two of the four links.

Your flat roll axis is good for reducing axle steer, but part of the stability comes from the higher roll axis provided by mounting the arms above the axle. This shortens the distance between the roll axis and sprung CG, reducing the level arm which results in less body roll. With any design, springs resist body roll. A sway bar in nothing more than additional spring rate to resist body roll withouth adding to ride-rate.

Won Ton, yer junk is looking mighty fine. Maybe it's time to represent the XJ community in the TTC.

 

[Beezil]

okay I removed a link......

now what?

no bind

maybe you need a bind eliminator kit.

 

[MrShoeBoy]

So why do the leafs need to be attached to the axle at all? I have seen a 3 link in action on a pick up that used the 3 link to locate the axle but the leaf pack was not attached to the axle. It just rested on the leaf spring pads on the axle. It worked well from the few trails that I followed the guy on. The only thing was it that it made lots of noise when the axle came back up to the spring and made contact. There was no limit to droop execpt the shocks so limiting straps would have been nice so when the ammount of "usable" travel was at the end, the strap would hold the axle to the frame and not the shocks.

AARON

 

[4ward]

I think Marky mark needs to come out with a Beezil eliminator kit.

I do have bind, albeit it's very minimal. You can't have links traveling in opposite arcs and not expect them to bind some.

Aaron, that is essentially what c-rok is running, although his is 1/4 ellip w/ airbag assist.

Max. That's what I get for posting at the wee hours of the morning. Mindless dribble that is only halfway articulated. I should have stated that the high roll axis is what alleviates body roll, too high and you run into problems also though. I'm still not understanding how you can expect spring steel to hold an axle in position. Don't you think that under acceleration, braking, etc. that the link/ spring is going to buckle?

I'm diggin' this thread, maybe I'll take Jes's advice.

 

[C-ROK]

Instead of the lowers being built from tubular stock, make them out of flat spring steel. There you have leafs serving as lower links and tubular, triangulated uppers.

Except that flat spring steel members have a tendency to deflect (warp, deform) when exposed to a high rotational torque induced compression load. Hence the axle wrap problem associated with leafs in the first place.

In the design you described the top of the axle would be held rigid by the upper links. Under high torque conditions the axle would tend to pivot about the upper link mount point and wrap the springs. This is hardly different from a full leaf spring except for with a pure leaf the pivot location will approximately be the axle shaft center line. All you've done is move the pivot location point and perhaps 'slightly' reduced the axle wrap potential but not eliminated it.
Not to metion the travel restrictions that the changing radius arc of the springs would bring as it fights the fixed radius travel of the upper link.

4-link and shackle both ends. You can even 3 link with leaves shackled at both ends but you accept a sloppy lateral rigidity as a result.
Detached leafs work too.
When all you ask the leaf spring to do is to be a spring and not a locating device, you can treat it just like you would a coil, or air bag etc.

I see that we're all enjoying the discussion but I'm not sure that we've really answered the posters original question; "Can I 4 link with leaves and leave my design open to accept coils in the future?"
Yes, you can. My recommendation is to shackle both ends of the spring. Detached leaf packs can be done but I do not like them personally and you need to have some method to reseat the spring to the axle. All the methods I've seen usually end up quite ugly.
Quarter elips and coils can all be done now or in the future.

 

[MaXJohnson]

I do have bind, albeit it's very minimal.


Max. That's what I get for posting at the wee hours of the morning. Mindless dribble that is only halfway articulated. I should have stated that the high roll axis is what alleviates body roll, too high and you run into problems also though. I'm still not understanding how you can expect spring steel to hold an axle in position. Don't you think that under acceleration, braking, etc. that the link/ spring is going to buckle?

I'm diggin' this thread, maybe I'll take Jes's advice.

"albeit"? Has anyone ever used that word in a post before?

Maybe I'm pissing up stream with this leafs 'n links thing, but I'll try to save it. Leafs usually have the center pin mounted forward so the front of the leaf is stiffer than the rear. Leaf stacking can also contribute to the forward stiffness. This causes the rear part of the leaf to provide more of the flex than the front. The stiffer front behaves more like a link similar to a radius arm. Add to this if the front of the leaf is acting as a lower link in a 4-link configuration, forces would be in tension and compression, rather than in beaming like a normal leaf setup.

Just thowing in some :arrowr: "OUTSIDE THE BOX" :arrowl: thought.

 

[4ward]

Max, there's only 1 way to find out, tell us what happens

 

[C-ROK]

"forces would be in tension and compression"

The leaves cannot resist with a tension force until the shackle has completely swung forward. The shackle, by design, allows the leaf to move fore and aft and thus it cannot resist a tensile force pulling the axle forward.

It really seems like the basis of your arguement essentially boils down to 'leaves work Ok at resisting wrap'.

You bet that leaves work like links. Thats one of the main reasons why leaf spring suspension have been used so extensively for so many years on so many vehicles. Because they solve so many problems all at once and are the epitome of simplicity and inexpensive to boot. A genuine "elegant" design if there ever was one.

But they have their weaknesses in the locating department. Our driving styles tend to expose those weaknesses too.

 

[TiRod]

This hurts my brain - or the Fresca -

I got it! The rear link setup is like a double A-arm turned sideways! Of course the wheels are 90* off, and you add the complication of a live axle tying the hubs. This requires even more coordination in the arm arcs to closely match travel requirements and eliminate steer. Camber is now 'pinion angle." Hmmm.

So, if I eliminate one bottom link, anchor it to the diff like a traction bar, and pivot at the tranny u joint, making a torque tube, the only steering effect would come from the triangulated upper links and leaf springs - a single long arm rear.

Downsides?