4x4 Suspension Handbook

PREFACE

This book is all about four-wheeldrive suspension systems and how they can be modified for better off-road performance. Unless you’re a four-wheel drive nut (and there are plenty of you out there) you probably won’t read this entire book. Instead, you might read the introduction and then skip ahead to the chapter that deals specifically with the type of vehicle you own. That’s understandable, but I encourage you to fully read the first two chapters, as they deal with the basic theories and terminology common to all 4×4s, old and new. I also encourage you to scan the other chapters, as they contain lots of little kernels of information that can be applied to other types of vehicles. Also, having a basic understanding of other suspension types also allows you to be better informed about the subject as a whole.

What you are going to see in the pages that follow is an in-depth explanation of the most common four-wheel-drive suspension systems—how they work, why they work, and their good and bad qualities. Furthermore, I explain how these suspension systems are modified for better off-road performance. Ninety-nine and a half percent of the time that means lifting them, and many well-respected companies out there have been building high-quality lift systems for decades. That brings me to what you won’t see in this book: The purpose is to provide a good knowledge base for the end consumer, not build a particular brand loyalty. The truth is that any suspension company that has been around for a while builds quality product; if not, lawsuits would have closed its doors long ago. In many cases, particularly with older vehicles, there is really only one way to lift a vehicle, and they all follow the same method. Other vehicles may have two or more schools of thought on modifying a particular suspension design; in these cases I explain the differences along with their advantages and drawbacks as objectively as possible.

Another thing you are not going to see in this book is how to design and build your own lift system, or how to modify off-the-shelf systems for more lift. The suspension system of a vehicle is a highly complicated and critically important component of a vehicle, and modifying them safely is well beyond the capabilities of your average shade tree mechanic. If you find yourself thinking it can’t be that hard, think again. I’ve seen a lot of butch stuff both on and off the road, and much more homebrew junk breaks out on the trail than off-the-shelf stuff. You wouldn’t machine your own connecting rods and pistons for your engine, would you? Fabrication should be left to qualified professionals.

Now, kick back with your favorite beverage and read on.

CHAPTER 1

SUSPENSION BASICS

Read This First!

While four-wheel-drive vehicles have been around in some shape or form since shortly after the invention of the automobile, we owe the four-wheel-drive systems as we know them today to the military. The need to transport men and materials to remote locations demanded vehicles with the capability of traversing muddy fields, ravines, hills, and rocky areas. By necessity, this meant all four wheels had to be able to put engine power on the ground. While many light, medium, and heavy-duty trucks were developed with this capability, most experts agree that it was the General Purpose Wagon, or GPW, that exposed the attributes of a 4×4 to the masses during World War II. Soldiers came to love the little¼-ton GPW and nicknamed it the Jeep, a name that stuck so well it became the name for a legend that endures to this day.

Though the WWII-era Jeep may not have been the first 4×4 to be produced, it was the one that brought the capability of a four-wheel drive to the masses. Surplus GPWs and the civilian models that were offered immediately after World War II were inexpensive and allowed former GIs the ability to take their families places no sedan or station wagon could. It could be argued that the CJ-2A (the first civilian Jeep) and the models that followed have largely shaped the 4×4 market as we know it today. (Courtesy DaimlerChrysler)

But that’s not where this story really begins. After the war there was a tremendous surplus of GPWs, and the military wisely decided to sell them off to the general public rather than scrap them. Returning soldiers, flush with cash, could pick up a surplus Jeep that they knew and loved for next to nothing. Furthermore, Willys Overland, the patent holder for the Jeep’s design, started churning out civilian versions (the CJ-2A) that were virtually identical to the military Jeeps, and these too were cheap. It wasn’t long before folks started tinkering with these Jeeps to individualize them and better suit their needs. Raising up the suspension in order to install larger tires and gain ground clearance was among the modifications made. The rest, as they say, is history.

Love them or hate them, there’s no denying that the Jeep is a big reason 4×4s are so readily available today, and just like those early days, 4×4 owners are constantly tinkering with them. While Jeeps are certainly going to be discussed in this book, they are not the only popular 4×4 these days. Chevy, Ford, Dodge, Toyota, and other manufacturers have all been building popular 4×4s for over 30 years. Without a doubt the most common major modification made to these vehicles is a suspension lift. No other modification enhances a 4×4’s attributes as much as a lift system, and an entire multimillion-dollar industry has been developed to satisfy a 4×4 owner’s quest for altitude. However, the suspension designs under 4×4s produced since the ’40s range from relatively simple systems with solid axles and leaf springs to incredibly complex Independent Front Suspensions (IFS). To further complicate matters, at least 20 companies currently offer suspension lift systems of various designs and lift heights. To the uninitiated, the options and complexities of all these different suspension systems can be bewildering. This book should help you sort through the morass by taking an indepth look at the most common suspension designs, and then walking you through modifying them safely and properly.

This chapter discusses the basic whys and hows behind purchasing a lift system. This is for the person that doesn’t particularly care about the nuts and bolts of a lift, but instead wants the basic knowledge and tools to make an educated decision. Chapter 2 contains a closer look at the individual components that make up a suspension system, as well as some of the technology that goes into developing and producing these components. The subsequent chapters contain an in-depth look at the five most common suspension designs utilized by the original equipment manufacturers and how they are modified for increased height and performance. Lastly, we spend some time looking at a number of high-performance suspension designs out there and provide a primer on some of the common hand-fabricated systems developed for a specific purpose.

Obviously, this book focuses primarily on off-the-shelf suspension systems; if you’re interested in fabricating your own, there are other books that are perhaps better suited to your needs. Should you want to fabricate your own suspension, some words of caution: An automotive suspension system is an incredibly complex network of individual components that must all work in concert. Designing and fabricating a safe and effective suspension requires an enormous knowledge base and an intimate understanding of key elements. The amount of work required is much greater than installing an off-the-shelf system, and requires a substantial financial investment that is easily double or more what a purchased lift system costs. Plus, engineering a system that is both stable and performs well is very difficult. In other words, there are only a few ways to get it right, but an unlimited number of ways to get it wrong.

One of the best ways to enhance the off-road capability of a four-wheel-drive vehicle is to increase its ground clearance by installing a lift system. A lift raises the body and undercarriage of a 4×4 to make more room underneath. This allows the vehicle to climb over obstacles without getting stuck. In this book, we take an in-depth look at the more common four-wheel-drive suspension systems, and then show you how they are modified for enhanced off-road utility. But before we dive in to the suspension world, a couple terms need to be made clear:

Defining a Four-Wheel-Drive Vehicle

Up until the 1980s it was clear which vehicles were four-wheel drive and which ones were not. These days there are a lot of cars and trucks being produced that are marketed as four-wheel drive, but are really more all-wheel drive. What’s the difference? For the purposes of this book, a four-wheel-drive vehicle (or 4×4 as is commonly used throughout this book) is defined as a vehicle capable of transferring power to all four wheels via a transfer case equipped with a Low Range and a selection that provides a true 50/50 torque split to the front and rear axles (usually marked 4-Hi). An all-wheel-drive vehicle typically does not have a Low Range and usually has a center differential that varies the amount of torque split to the front and rear axles. This distinction is being made because Low Range is specifically for off-road use and is indicative of a vehicle capable of negotiating rough terrain in a controlled fashion. An all-wheel-drive vehicle has the enhanced traction capability of a 4×4, but is more at home in slippery environments such as an icy or rainy road. These vehicles are not well suited for true off-road use and are rarely if ever modified for this purpose. Obviously, we deal with true four-wheel drives only.

Just because there’s not a lever on the floor does not mean it’s not a real 4×4! Many late-model trucks have push-button selectors for Hi and Low Range, and some even have a full-time four-wheel-drive mode as well as a part-time selection.

Off Road vs. Off Highway

Though the term off road is clear to many, it is important to explain how this term is used because it is something of a misnomer. Off road is defined as being on any established route that is not paved. Off road does not mean blazing your own trail across the desert or through the woods. Though the term off highway may be more appropriate, off road has become common vernacular, and as such is the term used in this book. It is every off-road enthusiast’s responsibility to stay on established trails on both public and private property. Obey any posted signs and report any violators to authorities. If we don’t follow the rules, we won’t have anywhere left to enjoy our sport.

A true 4×4 has a Low Range selection, indicated by the 4-Lo on the transfer case lever. Low Range slows the vehicle down and multiplies torque to the axles, allowing better control and increased power during off-road maneuvers. Vehicles without a Low Range are generally more comfortable on slippery surfaces such as ice rather than off-road, and most are based on car platforms. This, combined with the fact that not many AWD vehicles are popular among real off-road enthusiasts, is why not many aftermarket products are available for AWD.

Suspension Basics

By its most basic definition, the suspension system of a vehicle absorbs surface irregularities and prevents them from being transmitted to the passenger compartment of the vehicle. That sounds simple enough, but the fact of the matter is that suspension plays a part in much more than just smoothing out the bumps and dips we encounter on and off the road. Suspension plays a key role in overall vehicle performance; it’s what allows a road racer to take a corner at speed without losing control, what enables a drag racer to transfer power to the ground for a hard launch off the line, and what transforms a ride in a regular car and truck from a bone-jarring experience to an ordinary part of life. But for a four-wheel-drive vehicle, the suspension system is what makes or breaks its safety and performance on and off the highway.

Off-roading is what 4×4s are all about, but if we don’t respect the rules on public and private lands, we soon won’t have anywhere left to go four-wheeling. As you can see here, this rig is on an established, marked trail. Off-roading does not mean blazing your own trail or cutting your own path in the woods; this is destructive and gives those groups who would rather not allow motorized access to public and private lands more ammunition to deny the rights everyone should have, no matter what their conveyance.

When you mention suspension to most people, they associate it strictly with how comfortably a vehicle rides. That’s true, but it also plays a key role in getting engine power transferred to the ground by keeping the tires in contact with the road surface. It locates the front and rear axles of the vehicle, it controls vehicle stability by keeping the vehicle’s body and frame steady in corners, and it controls the distance maintained between the vehicle’s frame and the ground. So, there is a whole lot more going on here than meets the eye! The fact of the matter is that a 4×4’s suspension system must be able to do many things at once. It must be versatile enough for you to comfortably do 70 mph on the interstate, and then lock in the hubs and crawl over rough terrain off road.

The exact components that make up a vehicle’s suspension vary according to the suspension’s design, but at the most basic there are springs, shock absorbers, sway bars, link or control arms, and compression and extension travel stops. In addition to the suspension components themselves, a variety of other related components must also be included when you’re talking about lift systems. These include steering components, the axle assemblies, brake lines, tires and wheels, drivelines, and so on. Each of these topics is covered more in-depth in subsequent chapters.

If you ask any owner of a 4×4 how he or she wants to modify his or her vehicle, you’re likely to get lift kit as an answer. Why is that? A lift system raises the body and frame of the vehicle to create additional ground clearance. It also provides room for larger tires, which further enhances ground clearance and aids traction. In many cases a lift system also increases suspension travel, providing additional suspension articulation to keep the tires in contact with the ground while climbing over obstacles. Lastly, the motivation for many lift kit purchases is to enhance the look of the vehicle and make it stand out in a crowd. Whether you want enhanced performance or just want that lifted look, it’s important to know what’s going on underneath before you go shopping for a lift system.

What Lift Systems Affect

In a word, a lift system affects all of the components mentioned earlier. The important thing to remember here is that the axle assemblies are being moved farther away from the chassis of the vehicle, so everything that attaches to both the axles and the frame must be adjusted or corrected. The degree to which each component needs to be modified depends largely on the amount of lift. With a 2-inch lift, for example, very little may be required, while an 8-inch lift on the same vehicle requires addressing each of the items outlined below. Individual components are identified and discussed in Chapter 2, but here is an overview of the basic systems and components affected by a lift system.

Steering linkage / geometry

Perhaps the component most profoundly affected by a lift system, the steering linkage and its operating angles are critical. A lift increases steering linkage operating angles, and if left unattended these increased angles lead to a multitude of handling problems. These include bumpsteer, wandering, and in severe cases, linkage bind and premature failure. A variety of different methods correct the steering geometry depending on the linkage design, from dropped pitman arms to replacement centerlinks. The goal with any correction method is to bring the steering geometry as close to factory specifications as possible.

Even at a quick glance at this Twin-Traction Beam (TTB) front end, you can see several parts that have been altered to gain lift. The axle beams have been lowered via bracketry, there are new coil springs and shocks, the brake lines are longer than stock, the steering has been significantly altered, and even the sway-bar has been lowered. A properly designed lift takes into account all important vehicle functions that are affected by altering the vehicle’s ride height.

The steering linkage is what transmits driver-controlled input from the steering box to each knuckle. The linkage configuration varies from vehicle to vehicle, but it is critical that their operating angles remain as close to factory as possible or several bad steering and handling problems could result. The method for correcting the steering to work properly with a lift system varies, but this particular Jeep’s linkage was corrected with a dropped pitman arm.

Driveline angles

The drivelines, or driveshafts, of a 4×4 transfer engine power from the transfer case to the differentials. Every 4×4 has one for the front axle and one for the rear. When thinking about drivelines, you should be concerned with both proper length and operating angles. In the majority of cases, driveline correction is incorporated into the lift system design via degree shims (in the case of leaf springs), tapered lift blocks, or changing the rotation of the differential via drop brackets on an IFS system. Driveline length is rarely a factor at 4 inches of lift and lower, while some applications can handle 8 inches of lift without driveline modifications. As a general rule, the shorter the wheelbase, the greater the likelihood for driveline modifications. Front driveshafts are more problematic than rear shafts; they are usually shorter and their operating angles increase more quickly than longer rear shafts as lift height is increased.

Addressing driveline angles is just as important as anything else when it comes to lifting a vehicle. In the case of mild lift systems, little if anything is necessary as drivelines can be fairly forgiving. Even at 6 inches of lift, the rear driveshaft of this vehicle is stock. However, degree shims have been installed beneath the rear springs to tilt the rear axle pinion upward in order to relieve the operating angles with the lift.

Link arms (or radius arms as this example shows) are what properly locate the front axles of many vehicles. Link angle is often adjusted by lowering the arms attachment point at the frame via a drop bracket, as this example shows. With other applications, replacements links are needed.

Link arm geometry

Link arm is a broad label for anything that locates the axles under the vehicle, whether it’s a radius arm, control arm, track bar, or panhard bar. The operating angle of these link arms increase as the vehicle is lifted, which affects handling, driveability, and in many cases alignment. Link-arm correction takes many forms, including raising or lowering attachment points, replacement links, or lengthening the distance between the link arm’s attachment points.

Replacement brake hoses are commonly made of braided stainless steel and are anywhere from 3 to 12 inches longer than stock. The better ones have leaders, or formed metal sections that match an OE line and help guide the flexible hose away from the tire and other hazards. Also be aware that not all aftermarket replacement hoses are DOT-approved.

Brake hoses / ABS wiring

Just as critical as steering geometry, failing to address proper brake hose length is inviting disaster. Ironically, this is one area where people try to cut corners. Brake hose correction takes one of two forms, either lowering the brake hose attachment point at the frame or replacing the factory hoses with extended length pieces. In the case of replacement hoses, buyers beware, as not all replacement hoses are DOT-approved. On late-model vehicles, extending the ABS (anti-lock brake system) wiring is also required. Most lift systems accomplish this by re-routing the wiring or obtaining additional slack elsewhere in the system.

CV axles

On vehicles equipped with Independent Front Suspension (IFS), the CV axles transfer engine power from the differential to the wheel hub. (The differential is rigidly mounted to the vehicle.) Much like drivelines, excessive CV axle angles cause premature wear and failure. CV axle angles are corrected by lowering the differential housing and control arms.

Alignment

The mark of a quality lift system is the ability to achieve and hold factory alignment specifications. Alignment is addressed by a variety of methods depending on the suspension design and is influenced by a multitude of factors. Alignment is discussed at length in the subsequent chapters.

Ride quality

The most arbitrary of the factors listed here, ride quality is influenced by both the obvious factors, such as spring rate and shock valving, and more subtle items such as sway bar pre-load, alignment, and the tire-andwheel package. Most lift system manufacturers try to mimic factory ride quality in their designs while correcting factory deficiencies such as excessive body roll, brake dive, and vague or spongy driving characteristics.

Common Misconceptions Regarding Lift Systems

Lift kit design has come a long way from the early days of front lift blocks, re-arched springs, and backyard engineering. Lift companies today use the latest in computer modeling and modern manufacturing techniques in order to develop the products they sell. Some of these advances are due to the increased complexity of today’s vehicles, but much of it has to do with a greater knowledge base and the desire to build the best-performing, safest suspension systems possible. Even with the substantial growth and increase in technology, there are still some very common misunderstandings regarding lift systems and lifted vehicles in general. Let’s take a look at the most common: