What it does: A leaf spring, like a coil spring, is designed to set the ride height of the vehicle and it’s designed with a specific rate to ensure that the ride isn’t too soft or hard. Also like a coil spring, a leaf spring found in vehicles that carry heavy loads have higher spring rates. Variations found within the leaf-spring family include elliptic, semi-elliptic, three-quarter-elliptic, and quarter-elliptic. A leaf spring has a trait that a coil spring doesn’t have, in that it also locates the axle without the need for link arms.
What can go wrong: Leaf springs can crack from being overloaded, overextended, overcompressed, or simply due to age. When they crack it can cause the vehicle to lean, the axle can be out of center, or they may generate noise. The spring eyes (the circular part at each end of the spring where a bolt passes through the bushing to connect the spring to the hanger or shackle) can also break, which can cause the spring to lose its ability to lift the vehicle and keep the axle from shifting side-to-side. Sometimes the OE center pins can fail, which can cause the axle to shift. It’s a good idea to upgrade the center pin to a higher grade bolt if you’re experiencing this problem. Sagging leaf springs should be replaced and there are many companies that offer complete replacement springs, including Deaver Spring (www.deaverspring.com).
What it does: As a leaf spring flexes, its length eye-to-eye changes. Since a leaf spring is affixed to a solid hanger at one end, a shackle is located at the other end between the leaf spring and the vehicle frame to allow for movement. Bushings, rubber in OE applications and polyurethane in most aftermarket applications, are also used to allow the shackle to pivot. The shackle shown here is on a rear leaf spring of an ’05 Dodge Power Wagon.
What can go wrong: Like anything else, smashing the shackle into an object on the trail can damage it. If you live in a rust-prone area, shackles can corrode. The bushings used in the shackles can also wear. Summit Racing (www.summitracing.com) has a wide variety of stock and longer replacement shackles. Installing a longer shackle is an inexpensive way to get some lift, but doing this has downsides including an increase in pinion angle, a decrease in approach/departure angle, and if a really tall shackle is used, added side-to-side stress on the shackle hanger and spring eye.
Leaf-Spring Shackle Hanger/Leaf-Spring Hanger
What it does: Hangers are used to mount the leaf spring to the vehicle. Usually one end of the leaf spring is mounted directly to the hanger (this is called a spring hanger) while on the other end the shackle mounts to the hanger (this is called a shackle hanger). Hangers may be a small part physically, but since they are the mounting point for the leaf springs they play a big role. The leaf-spring hanger shown here is on a Dodge 2500 pickup.
What can go wrong: Hangers can eventually corrode due to road salt or age. If this happens, the leaf spring or shackle will lose its mounting point, which can result with the frame of the rig dropping onto the axle. Damage can also occur from contact with an object on the trail or even contact of the leaf spring to an obstacle, which can transfer the shock to the hanger. One of the many sources for new spring and shackle hangers is 4Wheel Parts (www.4wheelparts.com).
What it does: Lift blocks are often found in leaf-spring rear suspension systems. They are located between the axle and the leaf spring pack. Lift blocks have a hole in the bottom that receives the leaf-spring center pin or pins. Many OE 4x4s come with blocks from the factory, though some may use thin stacked pieces of metal (sometimes called a mini spring pack), as shown in this photo of a ’05 Dodge Power Wagon. Many aftermarket leaf-spring lift kits include taller lift blocks to raise the rear of the vehicle.
What can go wrong: Over time the U-bolts that connect the axle to the leaf spring can loosen, causing the block to crack or wear out the holes in the block. If a block fails, the result can be devastating to the rear suspension and/or axle. It’s never a good idea to stack lift blocks due to the potential for them to collapse if the U-bolts become even slightly loose. Lift blocks should never be used on the front axle due to the potential for failure resulting in a loss of steering control. Taller blocks enhance axlewrap and the longer U-bolts needed for the taller blocks can stretch and loosen up, so it’s a good idea to forego lift blocks and get new springs if you want lots of lift. Another lift option is a shackle flip kit, like the Offroad Design (www.offroaddesign.com) kit that’s available for 1967-and-up GM trucks. This kit includes brackets that allow the shackles to be flipped to create 2½ or 4 inches of lift without using lift blocks.
What it does: Overextending a suspension can be hard on parts. Depending on the suspension type, overextension can have several side effects from simply unseating the coil springs to damage of the ball joints, shocks, and tie-rod ends. It can even cause driveshaft overextension and/or bind. A limiting strap is designed to halt downtravel. Most limiting straps are made from nylon and include mounting buckles at each end. A strap is typically placed at each wheel, but sometimes a strap is placed in the middle of a solid axle setup to deter driveshaft separation. There are many sources for limiting straps including Off Road Warehouse (www.offroadwarehouse.com). This photo shows a limiting strap mounted on Jeremy Naeger’s Top Truck Challenge-winning buggy.
What can go wrong: It’s important to get the right length of limiting strap. If the strap is too short it’ll impede your vehicles suspension downtravel. If it’s too long it’ll be worthless. Limiting straps can be damaged by trail debris or obstacles or if they get pinched between components, so it’s good to inspect them often. Also make sure that your mounting points are strong.
What it does: Also called control arms, they’re used on solid axle setups. Link arms locate the axle longitudinally under the vehicle. Without link arms the axles would be free to move fore and aft. There are a number of variations of linked suspensions, but most stock 4x4s use a four-link arrangement with a track bar, meaning there are two upper links and two lower links locating the axle front to back, with the track bar controlling the side-to-side movement of the axle. One end of each arm connects to a bracket on the axle and the other end connects to a bracket on the vehicle frame or unibody. Shown here is the passenger-side lower link on a ’05 Dodge Power Wagon. Because the links must cycle with the axle, both ends in this application use flexible rubber bushings, but aftermarket links often use a rubber or polyurethane bushing on one end and a flex joint or rod end on the other to help increase their flexibility. Most aftermarket links are made from material that is beefier than stock and many are adjustable for alignment purposes.
What can go wrong: Road salt can do a number on factory links and their mounts. Bushings can fail due to age, heat, or oil. Some factory links are made from thin-walled material that can bend easily. If lower links come in contact with trail obstacles, they can be damaged. An example is the Toyota FJ Cruiser, which has weak rear stock lower links. All-Pro Off-Road (www.allprooffroad.com) offers its beefy Ultimate Lower Links for the FJ, which are not only strong, but include a Currie Johnny Joint on one end and a polyurethane bushing on the other to enhance suspension articulation. Chances are that there’s an aftermarket company that offers beefier links for your rig.