Stretch

[curtis]

Will probably be doing my stretch in the next few months. What do you guys think of a rear 3-link? I think the front 3-link I have now is by far the better set up.

[Dcope17]

I would go 4 link rear... 3 link would perform equally as well... but you will get more axle wrap with 3 joints on the axle rather than 4. ( and I'm talking something like a JJ which has some give to it )

[aw12345]

Actually a wishbone 3 link does not ride as nice as a 4 link. You'll get the axle to pivot around the upper ling center heim. Where as the 4 link seems to move gentler. Less jarring around. My little Jeep has a 3 link wish bone in the rear and the big Jeep a 4 link. Much prefer the ride of the 4 link. Do play with that 4 link calculator a bit to get things where you want it.

[curtis]

Well I think I might have said that wrong. This is what I want to do. Could be called a 4-link.



Art you and Fred were camped next to this jeep at the Hammers.

[aw12345]

Yup that's the way Campbell likes to built them. I like the offset diff which negates the other stuff.
Other than that a good 4 link works extremely well, negligible rear steer good flex and good handling

[inVERt'D]

Curtis, do a double-triangulated 4-link. Forget the rear 3-link and other options. Long answer follows.

there is only one good reason to prefer a 3-link in the front as opposed to a 4-link, and it boils down to your steering linkage. With a linkage type steering, you need the track bar to prevent bump steer. Without the track bar, vertical movement of the axle will push/ pull on the steering linkage, turning your wheels right and left. This is why the relationship between the the geometries of the track bar and drag link is so important: ideally the track bar controls the arcs that the axle can move in so that it can't push on the drag link. Some say that's a characteristic of crossover type steering, but a rack and pinion on your axle (thought occurred to me) would have similar problems. It's a solid axle with mechanical linkage problem. Unless you can design a triangulated 4-link which would allow you to eliminate the track bar and still prevent the axle from fighting the steering linkage, you need the track bar. If you have a track bar, you don't need the triangulation to control lateral axle movement, and in fact that 4th link becomes redundant, so why bother with the exhaust and PITA of a passenger side UCA on a TJ?

Now if you were going full-hydro, a triangulated 4-link without track bar would be better because properly designed, it allows more consistent geometry throughout the suspension cycle. A track bar makes the axle work asymmetrically, moving laterally in an arc.

Now back to your rear suspension. Assuming you won't be running steering linkages back there, you're better off eliminating the rear track bar. To do that you need either a sufficiently triangulated 4-link or 3-link wishbone suspension. 40* total separation is considered the minimum for good lateral stability.

A 3-link wishbone is basically a 4-link with 0" separation at the axle UCA joints. This isn't necessarily an optimal geometry for performance characteristics, and it's going to make your axle into a big torque arm putting all of its considerable leverage against that one upper balljoint. A 4-link can work better, so why bother?

So which 4-link? Three basic 4-link designs:

1. 4-link with trackbar Only reason for this design is a bolt-on kit that requires no rear UCA relocation. In other words, the easiest way for the aftermarket to extract thousands of $s from people.
2. 4-link with "straight" lowers coming off the frame rails: this design allows minimal triangulation for the lowers, depending on axle width--probably 5* or less on a stock width axle. To achieve the minimal 40* most of the triangulation must come from your UCAs. Since you're not going to get much more than 16" separation from center on your frame UCA joints, that limits how far apart your axle UCA joints can be and how long the UCAs themselves can be. If you want your pinion to consistently droop point higher up as the axle droops down, you need your UCAs to be longer than your LCAs. Challenging without a wide axle methinks. One good point to this is that you don't have to worry about your driveshaft or exhaust clearing a crossmember.
3. Double-triangulated 4-link with lowers coming off of a crossmember. Eliminates the constraints of #2. Put the crossmember far enough forward so you'll never have to worry about the driveshaft. I played with mine until I was totally convinced that right below the t-case output was exactly where it needed to be for a variety of reasons (except the exhaust). Like Art said, play with the 4-link calculator. Study other people's designs. One caveat: anyone who claims to completely understand and grasp this thing is either 1) full of B.S., 2. a genius on par with Nikola Tesla, who has spent considerable time studying and working with these things, or 3) too dumb to know better/ deluded

[curtis]

How does this sound to you.

Run the rear upper link just off-center to the driver's side, right next to the driveshaft, you counter-balance the driveline torque bias to the passenger-side making a more symmetrical reacting rear suspension. And you don't have to find upper-link clearance on the bottom of the tub.

PICTURE.

[inVERt'D]

Well it's a different way to approach the problem, and I like that about it. I don't like that the chassis will be forced to move laterally as the suspension cycles up and down. I don't like that the design is so sensitive to pinion angle and axle placement changes. What if you want the axle a little further back? Or you want to change the ride height? That track bar will be an issue every time you want to change something.

But if you just want to try something different, why not? As long as it's safe and makes you happy--have fun, be different, experiment. I can appreciate that. If it's about symmetry, why not have the driveshaft in the middle and symmetrical, triangulated links on both sides? True that torque is usually applied in one direction, but how does one upper link handle that better than two? To me it looks like a solution to a problem that started with an offset differential. Or maybe a solution to a problem that doesn't exist in the rear end?

I would like to hear more argument for the whole offset differential thing. At this point I don't think I like it. You need two different length shafts, hopefully not custom. I mean if I had the thing laying around in my yard and couldn't sell it to a Rover guy or something, I'd make use of it somehow.

Anyway, I'm not trying to be dogmatic--I want to learn too. I think hashing it out will make you feel better about whatever you do, so I'm here to help

[curtis]

Some great input David. The idea behind the differential is more clearance. You get hung up more on the rear diff. than the front.

[inVERt'D]

That's a valid point and Rover's reasoning behind it--lining up the diffs to simplify clearing obstacles. The exhaust will definitely be easier to route. I'll buy that much.

[curtis]

The way I look at it is rigs with 3 link in the front and 4 link in the rear get more usefull travel in the front then in the rear. So I like the idea of making the rear work like the front.

I have been working on this stretch for about 3 years. But rock crawling suspension keeps evolving to fast. SO every time I think I know what I'm going to do, a new idea comes out.

My goal is to keep up with the guys on fourtys and coilovers, with 35" or 37" tires with my coil suspension. After I get the stretch done I will need to put a bigger front axle in (9") because I will need to push it harder than I do now. I also think I need to hit 103" WB.

[aw12345]

37" tires and coilovers will work nice, yet still keep it fun to drive on the street. With antirocks front and rear it will handle pretty well and should have fairly even flex front to back. Will send you some video links of my last Cleggy outing it shows the body staying pretty level while the wheels just follow the terrain. Short armed TJ on coil springs will not do that any where near as well.

[inVERt'D]

The way I look at it is rigs with 3 link in the front and 4 link in the rear get more usefull travel in the front then in the rear. So I like the idea of making the rear work like the front.

I have been working on this stretch for about 3 years. But rock crawling suspension keeps evolving to fast. SO every time I think I know what I'm going to do, a new idea comes out.

My goal is to keep up with the guys on fourtys and coilovers, with 35" or 37" tires with my coil suspension. After I get the stretch done I will need to put a bigger front axle in (9") because I will need to push it harder than I do now. I also think I need to hit 103" WB.

So what's the problem with 103" and DT4L, even with mid-length (about 30") links? No problem at all. And a properly designed DT4L will not give you less travel than you can use--even with Johnny joints.

If the rear 4-links of the Jeeps of which you speak are limiting useful flex, then those 4-links probably weren't designed as well as they could have been. Limit straps are there to protect shocks, driveshaft, coil springs, brake lines--you name it, but links binding need not be a problem.

Why should the rear work like the front, unless it's doing the same job? Your front needs to steer, hence the linkage and track bar. Like the front, the rear needs to get power to the ground, but it's the primary power axle most of the time. If you want more travel, design your suspension for more travel. If you're going coil springs, I guarantee you that a properly designed 4-link will not be limiting your travel--if nothing else does, the coils will.

Rock crawling suspensions have developed a lot over the past 15 years. I would argue that your best shot at keeping up is going with the most mature and proven technology. The 4-Link rear is more mature and has more documentation than a 3-link + panhard. I would argue that all else being equal, you're better off with the linkage you can engineer the best. You can tune the crap out them--0* or so roll steer? Not a problem. Ideal antisquat--not a problem, and easily adjustable with multi-position link brackets.

Look at what most of the KOH cars have been running. Seems like these days at least it's mostly full-hydro fronts (no panhard) and a 4-link either with lowers off a crossmember or the frame rails. Look at Savvy's EMC overall winner: coil sprung rear DT4L--FTW!

The only way to go faster in a Jeep (but look gayer doing it) is to go IFS/ IRS.

[xthread]

Hey curtis .I;ll let u you use my jeep as a guiney pig first if you want.

[Dcope17]

the 3 link with a trackbar and a triangulated 4 link are both bind free setups. 4 link with a trackbar will bind.
3 link w/TB front for 2 reasons... Steering setup ( no full hydro ) and available room ( exhaust in the way ) 3 link front is a no brainer. Only problem I've had is with a hard stop... the Joints flexed enough and allowed my front axle yoke to hit my UCA and prolly throw a shower of sparks. I would like 4 links containing the front axle to keep hard braking from letting axle wrap put the yoke into the UCA. If I had the room to do a 4th link... I'd either have binding or if I triangulated and pulled the TB... I'd have bumpsteer. I chose to change from a 1330 joint and yokes to a 1310 for the extra clearance.

4 link rear because... I do not have the room under my jeep like in that pic... I pushed my rear D44 and stock diff cover to slightly rub the GTS at full bump which keeps my 35's out of the front of the fender wells where it is major bodywork to cut forward. Cutting higher and to the back is easy. With the axle at full bump... the UCA brackets almost touch the tub and the diff cover is at the GTS... there is no way a trackbar is getting through there. so with my full body jeep... to do a 3 link with TB... I'd either have to lift higher to get the same uptravel or the same lift and lose uptravel to make it work.

Lastly, my experience is building 1 Jeep. However, I have done at least a year of research before I started my build. I'm a fan of thinking outside the box... but I don't think this one is easily done on a full body rig and don't see any greater benefit for the extra work. Just my .02.