Thought I collate some information here and make a general information post on ways to lift your Eagle, the benefits and pitfalls of different methods, and what I've learned about the suspension. Some of the parts I'll discuss are not available for purchase and will require custom fabrication.
When it comes to lifting your Eagle you'll be dealing with two very different suspension systems, the front, which is an independent coil spring "SLA" type, and the rear, which is a solid axle leaf spring style. Let's discuss the front first, as it's the most tricky.
The relationships between the front suspension components can be difficult to understand at first glance. It is a complex moving system and any change can have unforeseen consequences. There are, in general, four ways to lift the front end. Coil spring spacers, upper ball joint spacers, spring perch spacers, and replacement springs. I'll discuss each of these in turn.
Coil Spring Spacers
Coil spring spacers are relatively simple, but are available in multiple style. The most popular is the "shim" style which is inserted between the coils to prevent them from compressing under static load. These have the benefit of relatively low cost and easy installation. They can provide several inches of lift without altering suspension geometry. They work by effectively "deadening" some of the coils of the spring, and this can have negative consequences on the spring itself. By reducing the usable length of the spring the remaining "unshimmed" coils are forced to carry proportionally more load. This can lead to early spring fatigue, resulting in springs "wearing out" or sagging quicker. In a worst case scenario this could lead to broken springs, although this seems to be very rare. Softer spacers will have less of a negative effect than harder spacers, but will also provide somewhat less lift.
Spacers which do not go between the coils (external spacers) do not have this same issue. Placing a spacer in the spring pocket, between the top of the coil spring and the body, does not reduce the usable length of the spring while still providing the desired lift. The only issue with this type of spacer is that the it reduces the length of spring which is "trapped" in the spring pocket and could lead to the coil spring becoming dislodged in extreme situations. To counter this the spring pocket's center section could be elongated, although this would only be necessary if seeking many inches of lift. Overall an external spacer is a good choice, with downsides only appearing at extreme lift heights. One thing to keep in mind is that if a coil spring has sagged severely and a tall spacer, either "shim" style or external, is used there is the possibility of "coil stacking", where the spring coils will contact each other. This causes serious spring wear and could result in breakage. However this can also occur in a stock vehicle if the coil springs have sagged severely enough to collapse, in which case replacements should be installed. It's important to note that any increase over the stock height achieved using shims will result in greater CV axle angle and increased angle of all of the suspension components, which will cause additional wear.
Upper Ball Joint Spacers
Upper ball joint spacers are a popular choice for mild lifts. They have the benefit of a very easy installation and low cost. However they can have several problems. They cause a change to the angle of the upper control arm relative to the lower. This is not generally an issue, or even noticeable by the driver, unless the spacers are excessively tall. Their main problem lies with the fact that they allow many of the suspension components to move in various directions further than they were originally designed for. To understand this I'll need to provide a brief explanation as to the hard limits of the front suspension.
The front suspensions upwards and downwards movement (compression and expansion/extension) is intentionally limited in two ways, by the bump stop that acts against the lower control arm, and by the shock, which acts on the spring perch, and by extension, the upper control arm. In addition, there are various components which would also provide limits if these were removed. For instance the ball joints can only pivot so far, and the same is true of the control arms. With no bump stop the suspension could only compress until the lower control arm hit the front cross member, or the shock bottomed out, neither of these are desirable. With the shock removed the suspension would expand until the bottom of the upper control arm hit the body, or the ball joints were at their maximum pivot angle, again this is not desirable. Any of these situations could cause damage to one or multiple components, if not immediately than certainly over time. Altering the position of the upper and lower control arms relative to one another also alters the maximum movement of other suspension components. This includes the CV axle, which will wear or break very quickly when used at an extreme angle. With this in mind lets return to the upper ball joint spacers.
By spacing the upper ball joints relative to the upper control arm we are effectively pushing every other component down. This, in turn, pushes the body (as well as the upper control arm, spring perch, spring, and shock) up. That means that when the suspension is fully compressed, and the lower control arm hits the bump stop, the upper control arm is pushed up higher than it was intended, which results in additional spring compression, more severe perch angle, more severe upper ball joint angle, and a more compressed shock. Likewise when the suspension is fully extended and the shock stops further movement the lower control arm is pushed further down than intended, the strut rod is at a greater downward angle, the lower ball joint is at a more severe angle, and the CV axle is also angled further downwards. Overall this results in more bushing flex, more ball joint movement, greater CV angle, and more spring compression than originally intended. In general, these components will all experience greater wear and shorter lifespans.
Now there is a certain amount of additional movement which can be expected with any replacement parts; for instance aftermarket shocks may have a greater extended length than the stock ones, and replacement bump stops may be slightly shorter or softer than stock ones. This is unavoidable and generally not an issue as the differences are fairly minor. However, combing tall ball joint spacers with longer shocks may result in extreme suspension extension, enough to cause one of the ball joints to be the "hard stop", which could damage or break them. Or, in compression, the coils of the spring may contact each other (coil stacking) which can cause tremendous wear or outright breakage of the spring, as in the case with spring spacers.
Overall, upper ball joint spacers, though popular, are not the best option for a front lift, but if they are to be used they should be limited in height, and one should keep in mind that other components may show premature wear.
Spring Perch Spacers
Lifting the spring perch relative to the control arm is not something which is commonly done, but has essentially the same pros and cons as using spring spacers. Similar to upper ball joint spacers, a machined piece of metal is installed between the spring perch and the upper control arm. This does not alter the control arm geometry, however it does alter the angle at which the coil spring and upper control arm interact. This causes somewhat more "in-and-out" movement (closer and farther from the engine bay) of the bottom of the coil spring relative to the top. This is not a serious concern unless the lift is excessive. A downside to this method is that it also alters the relationship of the shock to the rest of the suspension, causing greater possible maximum extension of the suspension components and a more severe CV angle.
A better way to accomplish this same effect is by altering the spring perch, or making a custom one, which is overall taller, separating the bottom of the spring from the perch pivot (and upper control arm) by the amount of additional lift desired + the original height, while maintaining the correct attaching height of the shock. This however, requires custom metalwork beyond the skill of most looking to lift their Eagle.
Replacement Springs
The final method for raising the front suspension is the most expensive, but arguably the best. Custom coil springs, or replacement springs, maintain all of the correct suspension geometry while allowing additional body height. The only downside to this method is the fact that increased lift will result in increased CV axle angle, as well as increased angles of operation for all of the suspension components. However, the same issues arise with any lift method, including coil spacers, or perch spacers. Ultimately the height of the vehicle was designed to be a certain way and deviation from it will result in increased wear.
Final Thoughts
There are many ways to mitigate potential issues, if you are intent on raising your front suspension, but the most important is lowering your front differential. CV axle angle is a great concern for lifted vehicles, wear, binding, and breakage are all possible, if not expected, with a lifted Eagle, and the only way to solve the issue is by lowering the front axle to compensate and return the CV angle to a more normal position. This process requires making custom brackets for the axle, as well as careful measuring. The front driveshaft of the Eagle is a slip-spline type equipped with U-joints, and so will tolerate some differential drop without much issue.
(Additional info from 89 MJ) Alternately, 1985 Chevy S10 CV axles can provide greater articulation before binding and can be used as a direct bolt-in replacement if CV binding occurs with stock axles. Be aware that CV binding may cause wheel bearing damage.
To achieve a greater ride height while avoiding suspension geometry issues, consider larger tires. A small lift (however achieved) combined with larger diameter tires can often be more impactful in overall look and feel, than a significantly taller lift with stock size tires.
Rear Suspension
The rear suspension could not be more different than the front. It utilizes two leaf spring stacks attached to a solid, "live", axle. This configuration is both robust and simple. There are 5 general ways to lift the rear; Blocks, longer shackles, more leafs, replacement springs, and re-arching.
The front of the leaf stack is attached to the body/frame of the vehicle with a rubber bushing, which serves as a vibration damper and compliance point. The center of the leaf is hard mounted to the top of the axle using u-bolts. The rear of the leaf is attached to a shackle with a rubber bushing, again as a vibration damper and compliance point. The shackle is then attached to the body/frame of the vehicle.
Blocks
"Blocks" or leaf spring spacers, are as simple a lift as possible. A piece of material is inserted between the leaf spring and axle, raising the spring relative to the axle. Typically longer U-bolts are needed to compensate for this additional height. Blocks are cheap, easy to install, and are effective. They are generally less stable than direct leaf-to-axle attachment and can shift under load, especially when cornering. Axle wrap is also a potential issue, although on a stock Eagle this is not usually a concern unless the block is excessively tall.
Longer Shackles
Increasing the shackle length is another simple lifting method. A longer shackle is sourced (usually from a jeep) or made. This separates the leaf and body more and, therefore, provides more height. However due to the geometry of the leaf spring suspension, the lift is only equal to half the length of the shackle. To get a 3" lift you would need to use a shackle which is 6" longer than stock. This quickly proves problematic as the greater the length of the shackle, the greater leverage it applies when cornering. Shackles can bend or break their mounting points, or fail themselves. In addition, shackle length change does alter the handling characteristics of the vehicle, typically increasing stiffness, though this may not be noticeable with small changes. Pinion angle change is another potential issue.
Adding Leaves
Increasing the amount of leaves in a spring pack is another common method. Adding a leaf or two will not simply raise a vehicle, but will impact the way the spring pack responds to static and dynamic loads. Depending on the length, thickness, and rating of the new leaf the suspension may be stiffer, or counterintuitively, may become softer. A new leaf, when added to a sagging leaf pack, may provide several inches of additional lift. However, the new leaf may also sag over time, sometimes quite quickly if it is a poor match for the application. Designing springs is a specialty skill which requires experience and knowledge beyond most home mechanics. It's best to consult with an appropriate expert before modifying your springs, but it remains an effective option with few downsides.
Replacement Springs
Similar to adding a leaf, replacing the spring packs entirely is a viable option. This is probably the simplest way to lift your Eagle, as it requires no parts-hunting or math, however, it is undoubtedly the most expensive. A properly designed leaf spring pack will provide as much lift as desired (within reason) with little downside. Ride quality, max load, and spring rate can all be customized to suit.
Re-arching Springs
Re-arching leaf springs is something of a "lost art", with many shops abandoning the practice and declaring it outdated or unsafe. However, re-arching is a relatively safe and effective method to restore your leaf spring to their original height or somewhat higher. It can be performed in addition to using blocks, longer shackles, and additional leaves, and if done correctly, the springs will settle no faster than they originally did. While re-arching can be done at home, it's recommend to seek a professional with experience in the practice. Re-arching to the original ride height has no negative consequences on vehicle performance or ride quality.
Conclusion
In stock configuration Eagles provide good handling characteristics, a comfortable ride, and more than adequate ride height for nearly all situations. However, for those wishing to push their vehicle to the limit, seek off-road adventure, or just like the look, an increase in ride height can be accomplished with relative ease at an affordable price.
Topic: General information on lifting your Eagle (Read 3558 times)