Review of the MORE shackle reversal and buggy leaf suspension on a Wrangler (YJ)
|On the RTI ramp at Sierra Trek, 1997|
|As with any suspension or steering modification the handling and safety of the Jeep is affected. In some circumstances this may be dangerous. We are only providing commentary and opinion based on our experience, your experiences could be significantly different. We cannot predict how any given modification will be used or what it will be subjected to. We do not recommend or endorse this or any product for any specific or general application. Anybody attempting this or any other modification does so at their own risk, we do not assume any liability.|
When the new Jeep Wrangler TJ came out in 1997 a whole lot of us with older Wrangler YJs developed a serious case of envy. Oh sure, the new 4.0 liter engine is nice, finally a serious rear end returned with the Dana 44 option, and many liked the return to round headlights. But what really sent most of us into fits of green jealousy was how well the new Quadra coil suspension worked. The TJ was definitely more comfortable on the street and flexier on the trail. Suddenly we were seeing new TJs with off-the-rack suspension lift kits scoring over the vaunted 1000 mark on the RTI ramp. Our old leaf sprung beasts seemed, well, antiquated in comparison.
Never fear, like any riverboat gambler we still have a few tricks up our sleeves, and there are still ways to coax a bit more performance out of the old leaf springs. Don't count our old dinosaurs out yet. Just repeat after me - "It ain't watcha bought, it's watcha built...."
Mountain Off-Road Enterprises markets a kit that is just such a trick. It is a kit that reverses the location of the shackle on the front springs (to the rear) and adds a secret weapon - a "buggy leaf" that is the kissing cousin to a 3/4 elliptic suspension. This kit affects suspension performance both on and off-road.
Like any suspension modification there are some tradeoffs that you need to consider before you decide to try this out
|Posed atop a rock on the Rubicon Trail|
Before we look at the details of the structure and installation of the kit we should touch on the subject of "Articulation". I suppose that for all of the theoretical mumbo jumbo tossed about trying to define exactly what articulation is and how to measure it, we are best left using a more practical description : Articulation is the ability of the suspension to keep the wheels in contact with the ground over uneven terrain and with sufficient force so that those wheels can provide traction.
Off-Roading in general and rock crawling specifically mean that it is very likely that you will be driving over stuff. As you drive one of your tires up and over an obstacle, if you have poor articulation it is likely that you may lift the opposing wheel (on the same axle) off of the ground. A tire can not provide you any traction if it is not in contact with the ground and if you have an open or limited slip differential all of the useable torque can be transferred to the wheel with the no traction (the one in the air). This could leave you high and dry and provide a great source of amusement for your buddies... "anybody got a strap?"
If you have good articulation, as you drive a wheel up and over that same obstacle the opposing wheel will stay in contact with the ground, it can then provide traction and the useable torque will be split between the two wheels. This is why most off-roaders will say that for rock crawling, the ability of the suspension to droop is more important than the compression travel available.
This is generally when somebody in the back of the class will raise their hand and try to tell us that even though the drooped wheel is in contact with the ground, there can not be much weight actually on that wheel and thus how much traction can that wheel really provide? The answer is: quite a bit!
To understand this first consider a vehicle sitting on level ground: If the vehicle weighs 2000 pounds over the front axle, then those 2000 pounds are evenly supported by our springs (we will only consider one axle at a time here) and each one is carrying a load of about 1000 pounds. If we had a spring rate of 200 lbs. per inch, then each of those springs is compressed 5 inches beyond its resting shape.
Now as we drive up and over an obstacle, we can see that the spring on the upside compresses more and thus is obviously supporting more of the vehicle's weight. Here we have to look at this like a lever. The wheel on the obstacle acts as the fulcrum. As the upside spring compresses it "pushes down" on our lever arm and exerts force on the downside wheel. Enough force can be transferred down our lever arm (the axle) to provide reasonable traction to the downside wheel.
Eventually as the downside spring moves past it's neutral position, it then fights this drooping action and when it finally balances out the force being exerted by the upside spring it lifts the wheel off the ground.
So you can see that we really want for maximum articulation is a suspension that has plenty of compression rate, but provides virtually no resistance to extension (or droop). A 1/4 elliptic suspension, with the spring riding loose above the axle does just this, and coil springs can be designed in such a way as well.
For us regular old leaf spring dinosaurs there are a couple of ways of improving this situation as well. One way, recently popularized by Glenn Wakefield - is the "missing link" shackle that can extend to provide more droop. Another way is through the use of 3/4 elliptic or "buggy spring" setups. In this setup the shackle from our regular leaf spring mounts to a section of spring that lies flat along the frame when the suspension is compressed, but can pull away from the frame when the suspension is in droop. The MORE kit uses this buggy spring approach.
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