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Now that I feel dedicated to this sport of Rock Crawling, have built many rigs, and truly feel that a properly suspended vehicle will make for a safer, more comfortable day of wheeling or road tripping I had few thoughts I'd share on how to set up a good suspension system using leaf springs and basic dampers and bump stops.
1. Set Ride Height 1st!! this is how tall the vehicle sits, too low and you will drag and have little to no up-travel, too tall and you will tip over easily and have minimal droop travel. I don't go by this whole new "ultra low" trend, because I know that if my rig is 1-2" taller than some of these slammed crawlers riding on bump stops I will have more up-travel, resulting in my wheels continuing to travel up, while the super-low crawlers are now hitting their bump stops and getting ready to tip over. I like spring rates that yield 1/3 up and 2/3 down travel. You will have to make adjustments to your mounting points if desired ride height and wheel travel ratio (up vs. down) can't be achieved with the stock mounts. Shackles don't always have to be at 45*. If using a leaf pack that is built with lots of thin leaves that will flatten out quite a bit, like the popular "rears up front" springs then your shackle is responsible for much less droop travel then if using a heavy, 3 leaf pack that won't flatten out too much. The latter style spring pack will benefit from a more slack shackle angle, simply due to the fact that the higher rate springs will not be under as much preload as the thinner, softer springs, and will not be in a position to release and offer as much down travel.
2. Bump Stops. You definitely want some nice forgiving bump stops. Set them up to engage just as the springs get flat, accounting for the "squeeze" of the bump stop to just barely put your springs into a negative-arch position when fully compressed. Taking the springs apart and only working with the main leaf can make this task pretty simple. I have used the hard " black triangle" type bump stops, and they are quite harsh. Yes, they keep your springs from over flexing, but can make higher speed offroading a nightmare. Also, if you can disassemble your dampers go ahead and install some shaft bumpers. Flex travel is different from straight on "speed bump" travel. Sometimes, your main bump stop will be for speed bump hits, and the shaft bumpers will only engage when the axle is fully articulated. Mounting the main bump stops a little inboard of the springs can help add to this effect.
3. Dampers. Now that the vehicle is at proper ride-height, wheel travel ratio is set, and bump stops are in place, you can get your dampers installed. You want the dampers to be as close to being inline with the wheel travel path as possible. This allows the piston to move freely within the body of the damper, minimizing bind, which can wear out many components of the damper, shaft, inner body surface, piston band, etc. It also allows the damper to work as it is supposed to, in as close to a 1:1 wheel travel to damper travel ratio as possible, not being over leveraged by being placed at an extreme angle, sometimes cutting damping characteristics in half. With a leaf spring setup it is ideal to take the spring pack down to just the main leaf and allow the truck to rest on the bump stops, adding a spacer block between the main leaf and the axle mount to imitate the rest of the leaves. Now you can get your dampers mocked up, and design an upper mount. I like to depressurize my dampers, but if using a non-serviceable damper that can not be depressurized you can just ratchet strap the dampers down. Right now, the truck is a full compression in a "speed bump" style bump. This is different from a rock crawling type of "flexed out" articulating bump. Articulation of the axle can allow the wheel to travel upward on one side of the axle once that side has engaged its bump stop while continuing to drop down on the other until the springs simply will not allow the lower wheel to droop anymore. For this reason, you want to set your dampers to have 2-3" exposed shaft when at full compression of BOTH bump stops on a given axle. Basically, if the weight of the vehicle is keeping the vehicle on the bump stops on all 4 corners you can now install your dampers with 2-3", I prefer 3", between the shaft and the bottom out point, not the shaft bumper (if you installed them) unless you are playing it extremely safe and running really long dampers.
A few things to remember...
-The front dampers need to be slightly angled inward so that the tire does not rub the damper or possibly the shock hoop, while trying to achieve that perfect 1:1 ratio, and not interfering with the steering shaft or other items under the hood.
-If you are trying to use dampers that are too short, set them up to top-out, rather then bottom out since top-out usually occurs at slower speeds, and bottoming out usually occurs at high speed, which can blow up a damper and/or mount. Obviously, if you are going through all the trouble of setting up your suspension properly then you are going to be using the correct length dampers, but just if...
-If this is a new rig build then you should also consider getting the steering set up at the same time. It's nice to know exactly how close that drag link is going to be to the leaf pack, and the fact that your truck is going to be sitting at full bump makes this the best time to get everything perfect. It also gives you an idea of how far back the axle will move during full compression. Maybe you don't actually have to chop up your radiator core support so much or at all?
-Spring clamps, yes, you need them. They can and will save so much headache on the trail. No more sledge hammering splayed out leaves, or broken leaves from de-arching on the trail.
-Springs will settle. Always keep some thin leaves on hand to adjust as necessary. I have had to add 1-2 leaves to a spring pack after just 2-3 months of driving and wheeling to get back to my desired ride height.
I would like to hear others input on this subject. I know all the rage is going to links and air shocks or coilovers, but how many people have actually taken the time to really dial in their leaf sprung truck? How many people are still running too short "white tube" dampers, bottoming out, running hard or worse no bump stops at all? Who is fine with their leaf springs, and what makes them work for you? Just some food for thought.