A properly designed 3 link will net you just as much travel as a 4 link. Just take a look at alot of Full Comp rigs. Alot of them run well designed 3 links and have more "Flex" then they know what to do with.

It seems to me your associating the panhard with the Stock jeep style parallel 4 link, which in that case the panhard does limit flex, but with a parallel 3 link, you dont get the bind you do as with the stock Jeep 4 link.

I realize that you seem pretty set in your ways as for as the suspension goes, but You defidently need to get on pirate and use google to search pirate for every 4 and 3 link thread you can find. It will help in the decision.

 

How does a bar that's connected to one end of the axle and the opposite frame rail not limit articulation?? As you droop the side where the bar connects to the axle (let's say lassenger side) the bar pulls the axle towards the driver side as the end rotates around the frame mount. Now, the effect gets smaller as the bar gets longer, but at some point even the best 3-link will bind as the bar tries to pull the axle out from under the truck towards the driver side. To me, this is a limit to how much you can droop that wheel from under the vehicle. It certainly does keep the drag link connection the same distance from the pitman arm thru the entire range of motion, but it also binds at extreme angles.

Now, with a triangulated 4-link, the triangulation of the upper links and the triangulation of the lower links (viewed from above, not from the side) locates the axle under the frame allowing it to move thru it's entire range of motion with no lateral movement. The axle will move front to back as the links rotate around the frame mounts (3-link does the same) but again, the longer the links, the less the effect. I understand that as the axle moves, the distance between the drag link end and the pitman arm changes causing bump-steer which is why my goal is to have the drag link parallel to the tie rod.

Assuming a 40" drag link (which I know is a bit long) and double the articulation I want for street driving (6" up and 6" down) the vertical separation between the drag link end and the pitman arm changes 1/2 inch. Now, unless I'm running full width axles (which I might) there's little chance of building a 40" drag link but I'm also shooting for 3" of uptravel and 3" of downtravel on the street so the effect should be less than 1/2 inch.

Now, if it's physically impossible to get the drag link within 1-5 degrees of the tie rod (or centerline of the axle which should be parallel to tie rod) then the amount of change will increase slightly but it shouldn't be significant enough to be a concern.

You mentioned the Jeep parallel 4-link and I think the biggest downfall of that design is the length of the links. With links that are only 18 or so inches long, the axle makes a very tight arc as it droops plus it uses bushings as opposed to heim joints which do not allow the links to rotate very well so it is doomed to have limited articulation.

Don't get me wrong, I'm not trying to say that 3-links are bad but if I'm going to reengineer and fabricate the suspension for my trail rig, I'm not going to take the chance of compromising articulation (the end goal) in favor of a vehicle that behaves like a car on the street when I can design an acceptable degree of bad behavior into the system without sacrificing articulation. If this was a mostly street driven vehicle or if I planned to drive it to the trails, then I would be more willing to make that compromise.

Pirate 4x4 is the reason I'm going 4-link and not 3. Believe me, I've done a bit of research.

 

But what good is all that suspension travel if it negatively effects your steering on the trail? Having a drag link is going to cause more then just crappy road handling. Everytime you flex the suspension, your steering is going to be effected even on the trail. If your flexed up and trying to turn but your turning radius has been diminished dont you think that is a very poor quality to deal with so you can maybe gain a couple more inches of flex? plus unless your going with a good length coil over, a 3 or 4 link suspension will always out flex a set of coils anyways. Im just trying to understand why your justifing the 4 link with all the cons of that setup.

The triangulated 4 link is a great setup but I think your going to find that if you do go that direction that the downsides of the setup you want to run will greatly out weigh the upsides.

 

Im not going to dissagree that it will eventually limit flex, but by the time it does that flex is no longer useable anyways.

 

If it turns out to be a detriment on the trail, then I will consider hydraulic steering. I would prefer to have to upgrade to hydraulic steering and have all of the flex than sacrifice flex to be able to keep the draglink which is inferior to full hydraulic steering anyway.

Regarding the springs, at this point I feel that my shocks are going to be the limiting factor so I will design around those and find appropriate springs. Coil overs could be in the future for the rig but I'm looking into air shocks as well.

The biggest thing I'm going to design into the system is flexibility. It will be done so that an upgrade from shocks/springs to coilovers or air shocks is as simple as possible and adjusting the geometry for anti-squat and pinion angles will be a one wrench operation. The overall design of the system is the one thing that I don't want to have to change once it's done so I only want to make compromises that can be overcome with simple upgrades. I will compromise and go with a shock/spring setup at first because of availability of parts and cost but can easily upgrade to coilovers when the time and funding comes. Hydraulic steering is never an "easy" or cheap upgrade, but it will not involve changing the link suspension so it's a compromise I can justify making now as long as I plan the upgrade into the design. Other than the possible need to change to hydraulic steering, I cannot think of any cons to a 4-link over a 3-link. Cost is not really a factor since I am designing and building it myself and would have to build a 4th link (panhard bar) regardless.

 

Tom I haven't seen the jeep in a while but have you flipped the tierods. I know they make a kit for your axle to flip it so it ends up sitting as high as the actual axle. Kinda a cheap high steer. Eliminating some of the need for the drop pitman plus once you reream the knuckles you can use 1-ton ends. I'm sure you have seen it before anyway.

 

And now back to your regular scheduled tech...

 

I havn't done that mainly because when I went sprinig-over-axle the drag link is really close to the passenger side spring (but never touches it) so I figured I'd leave it alone until the time comes to swap the front axle and/or eliminate the leaf springs. I got lucky that I have room for the link to miss the spriing tho because most people have issues there. I don't know why mine is different but I've been planning to do something different with the front end since I did the SOA and got lucky that I didn't have to dump too much money into the steering to make it work.

 

I really think John's Idea is good. Can we make this a sticky and place the SAS unders a Subcategory in the Suspension form. Post up if you are for this Idea.

 

Where did you get your drop pitman arm? I'm in the process of a SAS and am using the newer model 'yota steering box as you are. However I currently have the regular pitman arm - not sure if it'll clear the frame.

 

i think that maybe a stock pitman arm....

this is my box and thats the stock pitman arm on there, i think he just cut his TRE out of the end

 

One of the major cons to a triangulated 4 link is the side to side leverage the links have on axle. This is huge when using conventional steering (not full hydro). The drag link(steering) is putting a direct lateral force (levrageing off the frame) onto the axle trying to push it out from under the truck and because of the basic geometry of the triagulated 4 link, it is harder for the suspension links to counter act that. This problem grows as the links get longer becuase of the angle between the links and the frame. It can cause the front end to wander and become very unstable on and off road. This is another reason why you dont see many triagulated 4 links on the front of trucks UNLESS they are running full hydro.

If you design your drag link / panhard angles right, the effect of bump steer and diminished stearing radius when flexed is minimized. The key here is keeping them parallel and as close to the same length as possible. This allows the steering and axle to follow the same arc. A panhard should also not limit flex if designed correctly, like you said (redranger), many comp buggies use this same set up. A triangulated 4link causes the steering and the axle travel in different arcs......causeing loooooooots o' bump steer and sh!tty turning radius when flexed.

Please do not run this set up on the road... or please notify the city to clear the roads before you take it out.

Another con is oil pan clearence. Im not sure it would be a issue on our trucks but i know it is on other vehicles (i.e. taco's). If you are trying to keep the truck low this become an even bigger issue.

huh?....Coils dont limit suspension travel unless the sping is captured at both ends. The shock that is attached to that coil is what limits travel.

Coil-overs are over rated. You can design a coil spring/shock set up to do everything a coil over can. Yea they are cool and all but not really nessasary.

Some new thoughts-

On the newer trucks (mines a 99, not sure what exact years) the speed ring is located on the rear axle. If you have an AUTO, make sure you get another rear axle with a speed ring (i.e. NOT A 9in) or else your speedo and transmission will not work right.

On another note.....My truck has a 3in body. I ran into big issues with suspension/axle hitting the frame because the frame does not kick up like a convensional straight axle frame. I would reccomend taking the body lift off before you design your suspension so that you can maximize the clearence between the frame and axle.

Just some thoughts.....

Chris

 

that is the stock arm, i just took out the balljoint.

i bought a new arm at www.allprooffroad.com for 70 bucks, i planned on making the stock one work but couldnt get it off the box.

 

I know that some trucks have this problem, i think it is mostly related to the 98-99 years. but we will find out when i get my truck finished for the 2000 year.

 

VSS is in my tranny... theres it for the 04s