The job of a car suspension is to maximize the friction between the tires and the road surface, to provide steering stability with good handling and to ensure the comfort of the passengers.
-How It Works
However, Jeeps aren't ordinary vehicles...we like to play in the mud, dirt, sand, snow, and rocks...or ideally a combination of some/all of these. As such, we demand and need specialized suspension, or lift kits to take full advantage of our vehicles' abilities
Jeep Suspension In Action
Terms To Know
- The axle assemblies bear the weight of the vehicle, as well as house the differentials (gears and sometimes lockers) and axle shafts, and through the shafts connect to the four wheels of the Jeep. The two types of axles you need to be familiar with are the Dana 30 (The front axle of the Sport, Sport S, and Sahara) and the Dana 44 (The rear axle used in all JKs).
- The ability of one axle to move relative to the chassis. It is the measure of the ease with which tires stay in contact with the ground (and retain traction) on very uneven terrain.
- The degree of slope that defines the largest ramp or hill that a vehicle can travel over without scraping against the frame or underbody components.
As the vehicle moves over uneven terrain, the reaction from the vehicle's suspension to the terrain may alter the vehicle's line of travel.
- Also referred to as Jounce stops, are used to limit up travel of the axle and prevent contact between the tire and wheel well, which can damage either or both.
- Vehicle coil springs are compression type springs. These are meant to buffer or absorb the shock or traveling over uneven surfaces. Three types of coil springs you should be familiar with are Linear, Progressive, and Dual Rate coils. A linear type spring reacts to all compression evenly, meaning it will react the same to a large change in surface the same as a small change in surface. If you look at a Linear Coil Spring, the coils are even over the compression range.
Progressive coils react differently depending on the amount of compression to maintain a more even response regardless of the change in surface. If you look at Progressive Coil Springs, you will notice the top coils of the compression range are closer together, offering a softer ride at the top of the compression range (think "on road"), as opposed to stiffer off road compression.
Dual Rate coils are a variation of Progressive Coils with a more distinct difference between the top coils (softer) and bottom coils (firmer). Offering a even more balanced ride on road and off then standard Progressive Coils.
- Jeeps have two control arms per tire, an upper and lower control arm. These control the vertical travel of each wheel.
- A vibration resulting from a loose or worn part in the steering or suspension, such as a tie rod end, worn trackbar bushing, or mistorqued suspension bolts, and usually set off by hitting an uneven surface at a certain speed. It goes away after the vehicle is stopped. If not addressed, over time the vibration can cause damage to other components of the vehicle and exacerbate the issue.
- When returning to level ground from a descent, this angle indicates the degree of a slope from which a vehicle can depart without scraping or hitting the rear undercarriage.
All Jeeps have a slight rake from the factory (The front is even or slightly lower than the rear). Dive is typically associated with braking, where the front end pitches forward and down. This can be corrected with a lift, or even small coil spacers.
- Is simply the amount of down travel your suspension has. Its controlled by the control arm, shock travel, and by the sway bar link (if connected).
- The lowest point between the axles and the ground.
- When put under pressure by larger tires or heavy offroading, the front axles C's are prone to bending. Gussets are thick pieces of steel used to reinforce the front axles C's (the joint that connects your front axle to your front tires).
- The motion of a wheel that compresses its suspension. If a wheel is at full jounce, it is at the upper limits of its travel. The opposite of jounce is rebound — or wheel movement that decompresses a vehicle's suspension.
- Limiting straps are typically used when the shocks are longer than the coil springs to prevent the springs from coming loose from the spring pads and coming unseated, or when there are no bump stops (or inadequate) bump stops, to prevent tire/wheel well damage from contact between the two.
- Roll-center is the imaginary point around which the body leans in a turn and also around which it moves when the suspension flexes on a trail. There is one roll-center each for the front and rear suspensions. The location of each roll-center for most solid-axle suspensions is defined by the geometry of the track-bars (aka panhard bars). On late-model solid-axle Jeeps, the front track-bar runs in front of the axle from the frame on the driver’s side to the axle on the passenger’s side. The rear bar is behind the axle and the attachments are reversed. The actual roll-center is found by drawing an imaginary vertical line down the middle of the vehicle and another straight line between the bolts at the ends of the track bar (ignore the bends in the bar). The intersection of these two lines is the roll-center.
- A device used to dampen or reduce the amount of spring bounce after a bump.
- Helps protect the undercarriage from damage when driving off-road.
- The front axle is prone to damage in more than one area. An axle sleeve is welded or beaten into the shaft to prevent the front axle tube from bending.
- From full jounce to full rebound, this is the amount of vertical wheel movement allowed by the suspension.
- Jeeps are equipped with two sway bars, one front and one rear. The sway bar on a Jeep controls the vehicles body roll. Without it, the top heavy Jeeps momentum going into turns would cause the upper portion to lean (or roll). The sway bars dampen this effect, keeping the vehicle balanced above the four tires.
Sway Bar Link
- Also called "End Links" These connect the sway bars to the axle (one on each side, front and rear). Stock Jeep sway bar links are fixed with rubber bushings. Many aftermarket lifts include elongated or adjustable end links. These can also be disconnected offroad for a smoother ride and more axle articulation. However, make sure the end links are reattached before driving onroad in traffic.
- A truss is another method of reinforcing the front axle of a Jeep. trusses are attached externally by welding steel or aluminum along the top of the axle housing between the differential and C's
Basic Jeep Wrangler JK Suspension Components
1. Coil Spring Isolators
2. Jounce Stops
3. Shock Absorber
4. Upper Control Arms
5. Lower Control Arms
6. Control Arm Bushing
7. Track Bars
8. Sway Bars
9. Sway Bar Links (End Links)
10. Sway Bar Bushings
Types of Suspension
A Teraflex Budget Boost Kit
Budget Boost ($40 to $200)
- This is the most basic, or entry level lift. Typically a Budget Boost includes coil spring spacers (Rubber pucks), or coil spacers and shock extensions, and will give your Jeep 1"-2" of lift. Aside from price, budget Boosts are popular because they don't require many modifications to the suspension (driveshafts, alignment, etc). Used mostly for clearance of larger tires(typically up to 35") or very light offroading (think dirt roads).
An Old Man Emu (OME) Coil Lift Kit Coil Lift ($299 to $799)
- A Coil Lift typically includes stiffer, or longer coil springs which offer you 1.5" to 3" of lift. Depending on the manufacturer, these kits may also include things such as shocks, brake line extensions, bump stops, track bars and track bar brackets, and sway bar links. Where a Budget Boost is basically used to allow greater tire clearance, a Coil Lift is where you truly start seeing the benefits of lifting a jeep, gaining articulation and improved tire contact with driving surfaces.
A Rock Krawler Short Arm Kit
Short Arm ($1200 to $2500)
- A Short Arm kit most often includes everything found in a coil lift, with the addition of adjustable or elongated control arms. Because of this these kits typically run from 2" to 4" or more. The Short Arm lift kit offers even more articulation than the Coil Lift, without getting into major fabrication or suspension modifications.
A Rock Krawler Long Arm Kit
Long Arm ($2200 to $4500)
- The Long Arm lift for a Jeep is not for the feint of heart, requiring fabrication and welding, yet offering up 4" of lift or more. The Long Arm kits use longer control arms, and utilizing aftermarket brackets that require you cutting off the stock brackets and welding new, heavy duty brackets to the frame. The advantages of a Long Arm kit is pretty simple....insane crawling ability.
Old Man Emu
What kit should I get?
No one can answer this question for you....what you have to do is balance your budget with your needs. If you need nothing more than to clear a slightly larger tire, then you should price a budget boost.....but if you plan on running the Rubicon Trail, yet only have $500 to spend, look at a kit that covers the basics and allows you to add as you go.
What company makes the best lifts?
Again, this is dependent on you and your needs. There are several different companies that make good lifts....one may make a lift that handles on road fantastic while handling mild to moderate trails.....another company may make a lift that is soft onroad, but one that handles medium to hard trails perfectly.
How do I choose the right shocks for my lift?
The simplest answer is to contact the manufacturer of the lift you are considering and ask them what shock they recommend for your particular lift. If you have a specific brand of shock in mind, ask them for a model number that will work with your lift.
Why are my coil springs sagging?
A Jeeps coil springs can sag because they aren't strong enough to hold the weight they are supporting (adding a aftermarket bumper and winch can add up to 200lbs to the front of a Jeep), or because of age (as time passes the springs are compressed an uncompressed repeatedly, over the years they lose their spring). Sag can be countered by installing stiffer springs, and in the case where sag is caused by added weight, you can use coil spring spacers.
What issues can a lift kit cause?
It all depends on what you do to your Jeep. After a typical install you'll want to make sure everything is torqued to spec. Some people recommend an alignment. If you lift a JK 3" or more you'll need to start worrying about drive shafts. With a 2DR model the shafts are at a steep angle. On the 2012 models (especially the automatic) aside from the angles, the front shaft can come in contact with the exhaust crossover during droop, and the rear can come into contact with either the evap canister skid or gas tank skid (there are simple workarounds for both). These are just issues to keep in mind....some people never have issues with the drive shafts, others have to replace theirs soon after lifting their Jeeps.
Q: I installed a lift kit and now my Jeep shakes badly when driving.
A: You are probably suffering from the notorious "Death Wobble". Death Wobble is a vibration resulting from a loose or worn part in the steering or suspension systems, such as a tie rod end, worn trackbar bushing, or mistorqued suspension bolts, and usually set off by hitting an uneven surface at a certain speed. It goes away after the vehicle is stopped. If not addressed, over time the vibration can cause damage to other components of the vehicle and exacerbate the issue.
Q: I installed my lift and now my ESP light is coming on?
A: Your steering wheel is slightly off center, and your Jeep thinks its in a skid....this is an easy 10 minute fix. You'll need a 15mm socket or wrench, and hopefully a friend to watch the effect on the steering wheel as you spin the turnbuckle. Crawl under the front of your jeep and find the two nuts securing the turnbuckle, loosen the nuts and spin the turnbuckle clockwise or counterclockwise until the steering wheel is straight. Tighten turnbuckle nuts, drive the Jeep for a few miles to confirm the issue is fixed. It may take a few tries.
Q: I lifted my Jeep, is my stock jack now worthless?
A: Not unless you are running larger than 35" tires. Even though you lifted your Jeep, the ground clearance at the axles and differentials (jack points) are still the same. Other issues such as where you are will play a part (mud, loose dirt, snow, sand). A good jack base is always something to consider when going off road.
Q: Do I have to replace my shocks when I install a lift?
A: It depends. The stock JK shocks will handle up to a 2" lift. As your shocks are the limiting factor in your lifts down travel, you need to replace them with aftermarket options or shock extensions once you exceed 2", or risk damaging your vehicle.
Will a lift kit void my warranty?
This is a hotly debated topic. You'll hear people say their dealership voided their warranty after a lift. You'll hear some people who were told by their dealer that the lift is warrantied if it is dealer installed. The real answer is a bit more tricky.
The Magnussen-Moss Warranty Act states "Legally, a vehicle manufacturer cannot void the warranty on a vehicle due to an aftermarket part unless they can prove that the aftermarket part caused or contributed to the failure in the vehicle ".