Mustang Front Suspenstion and Upper Control Arm Rebuild Guide

These aftermarket lower control arms from Global West Suspensions begin life as factory stampings but get a few clever upgrades to make them better. The first of these is that the opening on the lower side is closed off (“boxed”) to greatly increase the strength of the arm. Special-cut plates are fully welded around each seam to completely close off most of the lower opening of the arm, so dirt and moisture cannot accumulate and cause rust. It’s not really possible to close off the whole underside because access must be left for the anti-sway bar end link nuts. The other major improvement over the stock arms is the use of a flanged spherical bearing instead of a rubber bushing at the end that mounts to the body. This type of joint is far stronger and more stable than a rubber bushing; it also has less friction, which actually improves the ride a bit. It is much less prone to wear and pounding out, plus the flanges help prevent unwanted movement of the adjusting bolts that are used to set the wheel alignment. Using bearings instead of bushings improves ride, handling, and durability while being virtually impossible to detect, unless someone crawls under the car to look. If we were building a racer or a higher-performance street car, we may have chosen tubular arms instead. Because we won’t be using the car that aggressively and we want to keep a stock look, this is the type of modification we want—one that greatly improves function with minimal change in style. This is a truly bolt-in upgrade that works very well indeed.

Another subtle improvement is the use of special “Lock Out” plates instead of the standard eccentric cams to adjust the position of the lower control arms. The factory eccentric plates have several inherent design weaknesses that can show up over time and/or with too much enthusiastic driving. The factory bolt has a flat side ground onto it that is meant to line up with a step in the offset hole in one of the corresponding plates. This basically indexes the plate to the bolt, so it cannot rotate on it; at least that’s the concept. The hole in the other plate is round so it can go all the way to the head of the bolt, and it’s free to rotate. The problem is that there is too much slop or tolerance between the flat on the plate and the bolt; they just fit too loosely from the start. Over time, the tolerance increases because of use and corrosion. It’s mainly friction and the clamping force of the bolt that prevent the plates from slipping, so you need to have as little play between the bolt and the plates as is possible. If the bolts loosen because of wear or extreme loading, it’s very likely the plates may move and throw the suspension out of alignment. A better approach is to use thicker plates with a series of offset holes, which are fixed in place by the same retaining flanges that locate the stock plates. The difference is that these new plates can’t rotate and the holes in them are much closer to the size of the bolts that go through them. This greatly reduces any potential for movement after the whole assembly is tightened down. Rather than loosening the bolt to turn the plate you have to disassemble the whole system and pick a different set of holes in the plates to get the position of the lower control arm that you want.

This side-by-side comparison of the stock eccentric-plate-style adjusters reveals the inherent advantages of the Lock Out plate. The Lock Out plates (left) fit the retaining flanges much more snugly and make much more contact along each side. The stockstyle plates (right) only have point contact with the flanges and fit more loosely. These plates are also thinner, so it is more likely they can flex under load and thus lose their adjustment as they move. It is also more difficult to keep the stock plates from moving during the adjustment process because the rotation of the plates affects their adjustment. The Lock Out plates are relatively restrained in the horizontal direction and can only move vertically during installation. Choosing different combinations of holes results in movement in both directions, but the plates are locked into position when resting between the flanges. The Lock Out plates are clearly a superior design for any application but are really only needed in higher-performance and/or racing situations.

Lock Out plates are designed so each plate can be repositioned to yield a virtually infinite number of possible locations for the lower control arms. There are six possible combinations of holes in each plate (three per plate with front and back variations), plus the plates can be rotated. This provides more than sufficient adjustment range to find the setting you need. Each plate is marked with numbers for each hole to help ensure the two plates at each control arm are properly matched with each other. There’s a trick in how the plates have to face each other, but it’s explained in the instructions that come with them. It’s a bit tedious, but you should only have to do it once because these won’t wear or move like the stock components. If you’re using lower control arms with flanged bearings, as we did, the plates shouldn’t move or deteriorate over time because the plates and flanges clamp are firmly clamped together. While it may take more effort to set the alignment the first time, you can rest assured it will be far less likely to change over time.

The finished control arm assembly is ready to be installed into the vehicle with the exception of the spring perch. That is discussed shortly. When installing the ball joint, note that relatively little torque is often required, sometimes only 18 ft-lbs. The force of the spring and the weight from the vehicle basically push down on the ball joint in the upper control arm so the bolts serve more to locate it than to help bear this load. Be sure to install the grease boot, but wait until the control arms are in the car and are loaded before fully greasing the ball joints. This is due to how the internal structure of the ball joint changes under load. The best approach is to lightly grease the ball joints when they are installed on the control arms and then go back and fully grease them when the load from the spring/car weight is applied. Grease the shaft, however, before the arms are installed. This is due to the difference in sealing technique and also the lack of access to the zerk fittings after the arms are installed. Make sure you fully seat the zerk fittings into the retention nuts else you may have clearance problems with the shock towers. Fully grease each side until you see grease just starting to come out from under each seal. Use the same type of grease you used.

Our choice of springs and shocks for the front suspension was fairly conventional, yet also quite an improvement. The valving of the Koni Classic shocks is optimized for applications like ours. They are designed for aggressive street driving and not competition, but they certainly can be used for mild track day events. Likewise, they are fine for daily use, though they are a bit stiffer than a regular replacement shock and they will cost more. They are extremely well made, high-quality, non-adjustable shocks that will surely prove durable in our situation. We chose slightly higher- rate springs from Global West Suspensions. These also lowered the car in the front to match the lowering we would be doing in the rear. This mild lowering gives the car a more desirable stance and also helps to lower the center of gravity for better handling and braking. The higher spring rate will stiffen the ride a bit but the tradeoff is worth it in our situation. The combination of slightly higher rate lowering springs along with the improved shock valving should complement each other very well.

Spring perches are one area that is often overlooked on early Mustang suspensions. These parts can often be the source of unwanted noise and handling issues. Any restoration project should involve inspecting their rubber bushings, at minimum. If the bushings are in good shape, these can be reused in a daily driver or even in a show car, if desired. It’s generally a better idea to replace them with new parts. The cost is low and the car is already apart. You can also upgrade to perches that use polyurethane (shown) instead of rubber bushings; we did, because the polyurethane minimizes unwanted compliance and can improve dynamic performance. There may be a very slight increase in noise and vibration, but we were willing to chance it. When using this material, be sure to use a part that has a provision for greasing the bushing because this minimizes the potential for any squeaking noises that can develop. A zerk fitting also helps improve durability because the grease reduces wear. It is best to grease the perches and rotate the shafts a few turns before installing them on the vehicle to make sure the grease is evenly distributed. Our perches were also plated to prevent rust and corrosion, a very nice feature. For the ultimate in functionality, some companies make spring perches that use bearings instead of bushings. These eliminate almost all compliance and reduce friction, though they also transmit more noise and vibration to the interior. They’re also more expensive, but this may be of no consequence to those building a higher-performance street vehicle or race car.