Mustang Rear Suspension Guide – Step By Step

When installing the springs and perches, ensure the lower portion of the spring is properly indexed to the perch. Here you can see the end of the spring resting against a stop that’s welded onto our aftermarket perches. The stock setup is a bit different, but it still requires the spring be rotated to the correct position. There is no insulator between the spring and the perch. Having one here would be of no value because there is one on the upper end of the spring, and the upper control arm bushings perform the same function at the opposite end of the noise path. Using one is undesirable, especially for a car that will be driven more aggressively, because it would add unwanted compliance to the suspension and negligible noise and vibration reduction. We left them out of our car; those building show cars should adhere to what the factory did, of course; the option remains open for daily drivers.

The factory upper spring isolators (on the right) are relatively thin and flimsy. The material used is also prone to getting brittle and cracking over time. Furthermore, they are designed to wrap around the coils of the spring and would not fit the thicker coils and flatter top coils of our Global West Suspension front springs very well anyway. We replaced these factory isolators with more robust polyurethane units. These fit better, lasts longer, and minimize unwanted compliance while still providing a reduction in noise and vibration. The inner sleeves also help keep the spring properly centered at all times.

If you will be using stock or direct-replacement springs with factory-style upper isolators, make sure the spring and isolator are properly indexed to the underside of the shock tower. As you can see in this photo, there is a special shape on the spring seat to accept the factory-style spring and isolator. The combination of shapes on the seat and spring, along with the friction of the rubber isolator, prevent rotation with the factory components. The lower spring perch merely supports the spring, but you must still ensure it is indexed to properly transfer the load at both points where the bottom coil contacts the perch. Our setup indexes the spring at the spring perch instead, so it’s necessary to line up the uppermost coil with the space in the spring seat. It wouldn’t be possible in any case because our polyurethane spring isolator makes no provision for doing so. It does, however, pilot on the raised edge of the upper spring seat to ensure the spring remains centered.

The front suspension is almost fully assembled. Note that you should never use an impact wrench to tighten the castle nuts for the ball joints. Doing so could seriously damage the ball joints. While it is acceptable to just snug the nuts using an impact gun or air ratchet, use a torque wrench for the final torque specification. Ensure all fasteners have been properly torqued and, where applicable, thread lockers or safety wiring have been used. Final joint greasing shouldn’t be done until the car is resting on the wheels; when the front alignment is being set, it’s time to grease the joints. We have not yet installed the front anti-sway bar and end links. The brake-line banjo fitting needs to be rotated to reduce the strain on it at full lock, but otherwise this is essentially what a finished stock-style suspension looks like. Obviously, it will be different for other vehicles, but the point is that we were able to install several significant upgrades while retaining thestock appearance. You can’t see the boxing of the lower control arms or tell they have bearings instead of bushings unless you really look for these things. Likewise, the upper arms are factory pieces, but even the spring, spring perch, and shock differ mainly in color rather than design. These could be painted to be less obvious but it’s unlikely those who use these components would. With few exceptions, these components install in a very similar manner to the factory components yet provide improved performance and durability without significantly departing from the original design. Those who want even higher-performance can install other, more extreme components.

Rather than retain the factory setup, we installed a largerdiameter, directreplacement anti-sway bar from Global West Suspensions to improve handling and reduce body roll. We felt this was fitting in light of the other suspension improvements we’ve made and the negligible effect this change would have on ride quality. In addition to the larger bar, the kit also includes new mounting brackets with firmer polyurethane bushing and new end links, also using polyurethane. These components allow significantly less deflection when turning, thus improving vehicle responses to steering inputs. These components go right back on where the factory parts come off. They only require some good grease inside the mounting bracket bushings to deliver enhanced performance with little, if any, perceivable loss in ride quality. These components should also be more durable, especially for cars driven hard. It is also possible to drill the mounting brackets and bushings to install a central zerk fitting to allow greasing the bushings in the car. We didn’t feel this would be necessary because we used tacky, high-quality waterproof grease. And we don’t mind dropping the bar to grease the bushings if we have to. There are, or course, much more exotic setups intended for vintage racers and higher-performance street vehicles, but these are not OEM or OEM-like and cost much more. Generally, they install in a similar way.

The final step to installing the front suspension is to secure the upper shock mount. We will be repainting the whole engine compartment to provide a more factory correct look and then paint the shock mounts to match. We have also installed the mounting brackets for the adjustable Global West Suspension Monte Carlo bar. Note, however, that the mounting brackets that come with this component are larger and stronger to better distribute the loads from one side of the vehicle to the other. The brackets are also secured by a total of four bolts, rather than the more common three-bolt setup, again to ensure strength and durability as well as reduced body movement under load. The overall integrity of the front section of the vehicle is improved significantly when the fully welded shock towers are combined with an improved export brace. This complements the improved stiffness of the center of the vehicle provided by the subframe connectors, plus the inherent stiffness of the rear leaf-spring system.

The components we’ve chosen are similar in design to direct factory replacements but have been improved in subtle ways to provide enhanced functionality. This rear spring kit from Global West Suspensions features higher-rate springs, which also lower the rear of the car by about 2 inches. It also includes upgraded shackles, hardware, and unique “Del-A-Lum” bushings instead of rubber or polyurethane bushings for the spring eyes. We also upgraded the shock absorbers and mildly reconditioned the spring plates and U-bolts. Note the construction of the Del-A-Lum bushings. These consist of a combination of metal and Delrin parts that allow for rotation of the spring eyes but prevent movement in other directions. This greatly improved the performance of the leaf springs because they are not able to twist or otherwise go out of alignment. Different thicknesses of side shims, also made out of Delrin, are used to properly position the springs and also to retain grease within the bushing while moisture and dirt are kept out. These bushings perform better than stock-type rubber or even polyurethane bushings, last much longer, and do not get noisy over time like the others can. The anodized color can make them a bit conspicuous if you look under the car, but this is a small price to pay for much improved performance.

It would make no sense to use the Del-Alum bushings in the spring eyes and then still use rubber or polyurethane in the frame rails. These special Del-A-Lum bushings go into the frame rails to resolve this matter. These are simply pre-greased and then pushed into place. Just as with their counterparts in the spring eyes, these bushings have side/thrust washers and provisions for grease fittings to allow adding more grease as is needed later on. Use tacky, waterproof grease as previously as other areas of the suspension. No steel inner sleeve is needed at either these rear frame rail bushings or in the bushings used at the rear spring eyes due to the action of the shackle that ties them together. The bushings in the front spring eyes, however, do utilize an inner steel sleeve for higher load capacity.

Whether using OEM or springs such as these Global West Suspension lowering springs, installation is similar. The Global West springs have a “reverse eye” design that lowers the rear of the car 1 inch or more. And the spring does not lose its shape as many other aftermarket springs do. This allows the spring to remain a rising rate/progressive spring that provides a softer ride yet still has the higher total rate needed for performance driving or even racing. This design also allows the spring leaves to remain thinner and lighter, thus saving weight while still preventing axle hop. When used in combination with the Del-A-Lum bushings, there is usually no need for traction bars because this spring/bushing system prevents axle hop. Higher cost, extra weight, and reduced ground clearance are penalties that would have been paid in most cases with such bars, but this system doesn’t suffer those penalties. And, it retains a relatively stock look in the process. Other than having to do an occasional greasing, there is nothing different about using this setup. The benefits are: virtual elimination of axle hop and spring binding; better ride; greatly improved handling at minimal extra cost; and no obvious change in the overall look of the vehicle. If you’re building a weekend cruiser and/or have high-performance or even racer goals, it provides the most cost-effective way to improve the rear suspension of your early Mustang and retain its overall design. While this may be more than is needed for a simple daily driver, it would be very beneficial in that situation too. The only thing Del-A-Lum bushings don’t improve is authenticity.

The shackle kit provided with our spring kit is critical to its proper function. The design of the Del-A-Lum bushings and the progressive leaf springs place higher and lateral loads on the shackles than a setup with rubber or even polyurethane bushings, because no force is dissipated in bushing compression. The finish and flatness of the shackles also must be different to accommodate the side/thrust washers, so they are able to rotate freely yet with minimal clearance. This precise fit and matching of components ensure optimum performance and maximum longevity. The combination of these shackles with the Del-Alum bushings virtually eliminates any lateral movement of the springs and axle, and thus minimizes the potential for tire rub in addition to providing improved handling. The compliance found in rubber and polyurethane bushings is such that significant lateral movement is possible even when a Watts link is used. A panhard rod by its very design introduces some lateral movement as it swings through its arc. The system we have chosen allows virtually no lateral movement, so the springs, axle, wheels, and tires move in an almost perfectly vertical path perpendicular to the longitudinal axis of the car. This effectively increases the clearance between the tires and the body because their relative motion is much more stable and predictable. Therefore, we intend to slightly increase the section width of the tires we use on this car to take further advantage of this characteristic and provide additional handling and braking benefits.

When installing the rear axle onto the springs, make sure the axle properly indexes itself to the locating pins on the top of the springs. Some axle-pad designs have a recessed piloting hole (right). If the locating pins on the springs are not high enough, the pins won’t go into these holes and the axle will be free to move on the spring—this is never good. The axle on the left will not have any problems because the pilot hole is flush with the mounting pad, and thus has to engage the locating pin on the springs and is positively held in place after the U-bolts are tightened. The solution to this problem, should it occur in your situation, is to use special inserts that effectively extend the piloting hole in the spring mounting pad so that they properly engage the locating pins. There is no need to weld these inserts to the pads because they are designed to fit the pockets in the axle mounting pads very closely. The tightened U-bolts cannot move off of the locating pins, and the axle mounting pads cannot move off of the inserts. In effect, the inserts expand the pins to fill the shape of the pockets in the axle pads, thus preventing movement. We were able to reuse the stock U-bolts and spring pads, so we media blasted them and painted them before we reinstalled them. There is very little to go wrong with these, but they still do need to be checked that they are properly indexed on the springs. In addition, there should be no rust or damage, etc., that could lead to subsequent failure. If you are not concerned with strictly original looks there are also spring plates that incorporate built-in tie-down loops to help secure a vehicle to a trailer. We don’t plan on trailering our vehicle very much so we did not use them but they may be an appropriate option for certain types of show cars.

This finished rear suspension reveals a close-to-stock appearance, except the colors of certain components like the Koni Shocks and the Del-A-Lum bushings. Of course the rear brakes and brake lines are not authentic, either, so the differences in component color are minor by comparison. We willingly made these tradeoffs to realize the significantly enhanced functionality these components provide. The Koni shocks are a dramatic improvement over a stock replacement shock, just as those used in the front suspension were. Their valving is optimized for performance driving and their durability should be far better than standard shocks. They are not adjustable, but we don’t need them to be. The benefits of the springs and bushings have already been covered with the exception of one final point: the use of the Global West Suspension springs and bushings we’ve chosen also eliminates the need for a rear anti-sway bar. This is primarily due to the virtually complete elimination of lateral compliance along with the rising-rate characteristic of the springs and the superior dampening of the Koni shocks. This saves a considerable amount of weight and cost. It also eliminates potential clearance issues with other components and the need to perform maintenance on the anti-sway bar bushings and end links. Using optimized bushing, spring, and shock designs eliminates the need for add-on components, such as traction bars and anti-sway bars. This reduces cost, complexity, and weight while also providing improved durability. These optimized components install just like the factory components with very minor exceptions and they look very similar to them as well. They may not be desirable for a show car where authenticity is a priority, or a daily driver, where budget is a greater priority than performance, but they’re sure a great way to go for the performance-oriented weekend cruiser we are building.