Shelby Drop (
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A Little History:
-The Upper Control Arm, or UCA drop AKA Shelby Drop, or Arning drop, is one of the more beneficial and easily the most cost effective suspension upgrade that can be made to a 1965 to 1970 Mustang (also works for Falcons and Cougars). This simple act of lowering the mounting point of the upper control arm does more for the way a classic Mustang handles than many expensive aftermarket components, and the best part is, other than the cost of your time, the modification is free, or almost free. Most refer to this performance upgrade as the Shelby Drop. This is due to the fact that the only Mustangs that arrived on the showroom floor with this modification were the 1965 and early 1966 Shelby models. The UCA drop was just one of the many modifications made by Shelby and his crew to these Mustangs. Even though most refer to this modification as the Shelby drop, in all actuality, if this modification were to be more accurately named we would call it the Arning Drop. Klaus Arning was a Ford suspension engineer who designed this modification to go with a rear IRS system he had designed for the early Mustang. Ford decided against the beter camber UCA location on the production line, however Arning was able to pass the info for the UCA relocation on to Shelby, who incorporated it into his cars.
-Most likely the reason ford located the UCA where they did was to create a camber curve that lent it self to understeer. Understeer is a situation where due to slight traction loss in the front wheels the car does not corner to a degree of sharpness that the angle of the tires would suggest. It is common practice among automobile manufacturers to configure production cars deliberately to have a slight understeer. If a car understeers slightly, it tends to be more stable (with drivers of less ability) if a violent change of direction occurs, thus improving safety. This does not mean the UCA drop is unsafe, it just means if you are going to make the steering more responsive and you need to drive the car with that in mind.
What Does The UCA Drop Do?
-Three factors make lowering the UCA an improvement in handling. First, this modification to the suspension lowers the center of gravity on the front of the car; second, body roll is reduced by 7% to 9%; and third, the camber curve is improved.
-The center of gravity is a geometric property that relates to any shape, but to keep things simple and related to the topic of automobiles, it is basically the internal balancing point from all directions of a car. When you do the UCA drop, you moderately lower the overall height of the front of the car, which in turn lowers the center of gravity. Easier understanding the application of the center of gravity and how it plays a role in vehicle stability can be illustrated by looking at the stability changes in a canoe based on passenger position. If you sit down on the floor of a canoe (low center of gravity) then the boat is extremely stable and nearly impossible to overturn. If you rise up and sit on the seats, the canoe becomes noticeably less stable, but still functional. Finally, if you stand up in a canoe (high center of gravity), the boat becomes completely unstable and will most likely overturn. In the same way the lower the center of gravity is on a vehicle, the more stable it will be.
Body roll is a major issue in classic Mustangs. The structure of the Ford Mustang is what is referred to as a unibody design. This means that rather than a stiff full-length frame, the body is built in such a way that it is self-supporting. This design is lighter and was more cost effective for Ford, however, during cornering, especially as you first enter and begin to exit a corner, the Mustang body flexes and results in reduced handling accuracy. When you lower the UCA, you reduce the leverage that the UCA has on the inner fender/shock tower, which in turn reduces the force applied to the body during cornering and thus reduces body roll.
-The biggest improvements afforded by the UCA drop come from an improved camber curve. Camber is the leaning in or out of the tires. The more negative camber you have the more rubber to road contact you have. If the top of the wheels leans in toward the engine compartment, the wheel has negative camber, whereas if the top of the wheels leans out away from the engine, the wheel has positive camber. In the same way, during cornering or when encountering inconsistencies in the road, if, due to suspension travel, the top of the wheels leans in toward the engine compartment, the wheel has a negative camber curve, or if the top of the wheels leans out away from the engine, due to suspension travel, then the wheel has a positive camber curve. The stock camber curve of the Mustang is positive so, as you corner or if you hit a bump, the top of the wheels leans out, reducing camber, and thus, reducing rubber to road contact which results in inferior handling. By relocating the UCA, the Mustang camber curve is changed from positive to negative, which significantly improves handling. Also, another added benefit of the UCA drop is that the arc of the camber curve is flattened, which results in a much smaller change in camber during full range of suspension motion. So, the camber of the wheels stays closer to the specification it was aligned to during a full range of suspension motion.
Spring Compressors 101:
-Performing the UCA drop requires compressing the coil springs. Failure to safely deal with coil springs can result in serious injury or even death. There are three main ways to remove coil springs: external claw type spring compressor, internal claw type spring compressor, and a bolt-in type spring compressor.
-An external claw type spring compressor consists of two separate pieces that clamp onto the outside of the coil spring. As the nuts on the two pieces are tightened down, the spring is compressed. There are three main issues with this type of compressor. First, both sides need to be tightened an equal amount and, since each piece has its own tightening nut, this is easier said than done. Second, this type of compressor REQUIRES that the two separate pieces be opposite of each other. Unfortunately, the shock towers of a classic Ford do not allow the two pieces to be positioned completely opposite of each other, which create an unstable compressed spring. Third, the claws of the compressor are held to the spring by tension from the compressed spring. If the claws slip, the spring can decompress violently. Many chose to use this type of compressor because they are inexpensive and can be purchased for less than $30.00.
-The second type of claw spring compressor is an internal unit, which has four claws (two at the top and two at the bottom) that grab an upper and a lower coil of the spring. One tightening nut pulls the two sets of claws closer together and compresses the spring. This compressor is much better for a Mustang then the above mentioned external claw type, however, it is still not the best option. There are two main problems with this type of system. First, often times on a classic Ford, a 3 to 4 inch spacer (usually a piece of pipe) is required to be positioned between the upper claw assembly and the tightening head to keep the compressor from bottoming out in the UCA. Secondly, as with the external claw type, the tension of the compressed spring is all that holds the compressor in place and, as before, if those claws slip, the spring can decompress violently. It was this type of compressor that sent me to the emergency room in June of 2005. After already removing the passenger’s side spring, I was working on the driver’s side assembly and had compressed the spring and was in the process of removing it when the compressor slipped, the spring decompressed and pinned my right hand by the three middle fingers palm side up, between the bottom of the coil spring and the spring perch. Engaging this type of compressor requires using two hands and, of course, I was alone, the garage door was down, my cell phone was on the passenger’s side fender out of reach and most of my tools, at least any that could have been effective in freeing my hand, were on the floor next to the passenger’s side where I had already pulled the suspension apart. All I had within arms reach was the ½” box wrench (no more than 6” long) that I had just used to remove the shock. I jammed the wrench in between the spring and the perch and was able to pry the spring up enough to get the finger next to my pinkie free. I then pried on the opposite side and got my index finger free. To get my middle finger out, I pried again with the wrench and pulled as hard as I could with the trapped arm and got my hand out. To make a long story short, I still have all my fingers and they still work, however, I occasionally feel some stiffness in the middle finger joints. I was lucky!!!!! Needless to say, it is my personal mission to convince everyone to use a bolt-in type compressor.
-The third type of spring compressor is the previously mentioned bolt-in type compressor. This compressor bolts to the spring perch and the top of the shock tower, just like a shock. Once the spring has been compressed, there is no way for it to come loose unless you intentionally decompress the compressor. The “down side” to this type of compressor is that in order to completely remove the spring, the UCA needs to be removed to get the spring out. This adds about 15 minutes to the task of changing springs, however, that 15 minutes is well worth the improved safety factor. See my spring compressor page for details on how to build one yourself.
Performing the UCA Drop
1. Remove shocks and Install spring compressor
-The first step is to remove the shock and replace it with a bolt-in spring compressor. Believe it or not, I have found that it is much easier to do much of this part of the job with the car on the ground. When the car is still on the ground, the UCA is almost parallel with the ground and, with the UCA in this position there is easy removal of the shock nuts and the spring perch nuts. Also, with the car on the ground, the spring compressor can be just as easily installed and the weight of the car helps to compress the springs, making the tightening of the compressor much easier.
2. Compress spring, Unbolt spring perch from A-arm
-As mentioned above, with the car still on the ground, compress the springs about 1” to 2” lower than normal ride height, then slowly jack up the car. Since the nuts that hold the spring perch to the UCA have been removed, the spring perch should pull free of the UCA as the car body rises and the suspension drops. As the suspension drops, make sure that the brake hoses are not supporting the weight of the suspension
3. Remove UCA, Support the hub, Save shims, and Inspect UCA
-Once you have the spring perch free of the UCA, remove the two nuts that hold the UCA to the shock tower. Before you pull the UCA free of the shock tower, reach behind and remove any shims (cars before 1967) and keep track of what shims went where. I always wrap mine with masking tape and label them so I know exactly where the suspension settings were prior to the modification. Also prior to UCA removal, I recommend placing a 6 X 6 block of wood under the Lower Control Arm, LCA, so that, once the UCA is removed, the weight of the spindle and brake assembly is not on the brake hose. Remove the UCA and shift the assembly to the rear of the car, making sure that there is no undue strain put on previously mentioned brake hoses. There is no need to remove the UCA from the spindle, however, if you have not already done so, this is a good time to rebuild the UCA bushing for improved grease ability and extra positive caster (see information below). At the very least, you need to inspect the UCA to ensure it is in reusable condition, as well as inspect the ball joint and pivot bushing.
4. Decompress and remove spring
-With a bolt-in type compressor, the spring perch is bolted to the compressor and holds the compressed spring in place. That means one could, in theory, perform the UCA drop without removing the springs, however, I do not recommend this. Compressed springs can be dangerous to work with and I would much rather take the few extra minutes required to decompress the spring and remove it than to be working in direct contact with a bomb (I mean compressed spring) waiting to go off. Loosen the spring compressor until all spring tension is eliminated, making sure the spring perch does not catch on the frame rail at the base of the shock tower, and then remove the tightening nut from the compressor so that you can drop the spring perch, spring and compressor out of the shock tower as a unit and set them off to the side.
- Bolt in template
-The physical specifications of the UCA drop for Falcons and Mustangs 1960-1966 are 1” down perpendicular to the centerline of the original UCA mounting holes and 1/8” back along the centerline of the new holes locations. The physical specifications of the UCA drop for Falcons, Cougars and Mustangs 1967-1970 are 1” down perpendicular to the centerline of the original UCA mounting. A paper template can be used to drill the new holes, however, for ease and accuracy, I recommend making or buying a guide template that can be bolted into place using the original UCA mounting holes, and then used to drill two 1/8” pilot holes. Steel templates can be purchased from my For Sale page. The main advantage of using a steel template rather than a paper template is that you have the opportunity to measure the pilot holes to ensure accuracy prior to drilling in the shock tower. When using a paper template, said pilot holes are drilled directly into the shock tower and, if their location is off, relocating them can be a challenge. The only time the pilot holes locations would be different than the above mentioned is if performing an “improved positive caster drop”.NOTE:if performing this modification on a car made before 1967 or if you are performing an improved positive caster drop, make sure the new holes are located to the rear of the car. If you bolt in a steel template backward it will cause you to drill the pilot holes towards the front of the car. Information on improving caster through the UCA drop is located below. Once the 1/8” pilot holes have been drilled, the template can be unbolted and used on the other side.
- Drill holes 17/32”
-The steel used to make the shock towers of these early Ford cars is probably the hardest steel on the vehicle. Because of this, I recommend drilling out the holes one size at a time, starting with 1/8” and going up no more than 1/16” at a time, but preferably 1/32” at a time. Using a step drill bit can easily facilitate this. The final drill bit size needs to be 17/32” and can be purchased on myFor Sale page. It is well worth it to purchase the correct size drill bit rather than worbeling the hole out with a ½” bit or increasing the size with a file. The hole needs to be just bigger than ½” so that the UCA can be easily installed and removed and also, on the pre-1967 cars, so that the UCA can be moved easily when installing alignment shims.NOTE:when drilling the holes make sure that you are not drilling into any parts in the engine compartment other than the shock tower. When I did mine, I placed a piece of 1/8” plate steel between the shock tower and my header tubes to ensure I didn’t puncture them.
- Reinstall spring
-Once the new holes are drilled, it is time to put everything back together. Start by taking the spring compressor, spring perch and coil spring assembly and reinstalling them back into the shock tower. Once the compressor is back in place, install the spring compressor tightening nut and begin to tighten it down. As you tighten it down, make sure the spring perch stays correctly positioned with the spring stop in the back toward the engine compartment. The spring compressor will need to be tightened to the point where the A-arm can be installed.
9. Inspect suspension stop, Install A-arm including shims
-Prior to reinstallation of the UCA, it is important to make sure that the rubber stops on the under side of the shock tower are in good shape. If these stops are damaged or missing, it is possible for the suspension to travel to an unsafe position, which can cause ball joint failure. Once stops are deemed sufficient, install UCA in the new mounting holes and install the spring perch mounting bolts into the UCA. You may need to tighten or loosen the spring compressor just a bit to effectively position everything. Install the spring perch nuts and the UCA nuts, remembering before you tighten the UCA nuts down, take the shims you removed earlier (pre-1967 cars), remove 1/8” to ¼” of them (removing the same amount from all four sets) and install them between the UCA and shock tower in the position they came in. Tighten down the UCA bolts and spring perch nuts and torque to factory specs.NOTE:the rear UCA bolt comes through near a small metal ridge on the shock tower in the engine compartment. Some people tighten the nut down onto the ridge but I personally choose to grind down one side of a washer and install it between the shock tower and the nut so the nut doesn’t hit on the ridge.
10. Install wheel, Lower car, Remove spring compressor, and Install Shock
-Once you have the UCA and spring perch/spring assembly installed and all nuts and bolts have been torqued to factory specifications, you can install the wheel and lower the car back down to the ground. As with step 1, removing the bolt-in spring compressor and installing the shock is much easier with the full weight of the car on the ground.
11. Modify other side
-Once one side has been modified, repeat steps 1-10 on the other side. After both sides have been modified and are put back together, it is now time for the final step, which is to have the car aligned.
Having the car aligned:
-There are several things to keep in mind when having your car aligned. First, factory Ford settings WILL NOT make for a good handling car. The original Ford settings were created with tires made in the 1960’s in mind and are not the ideal settings to maximize performance. Second, make sure you trust the alignment shop. Aligning an early Ford can be very challenging, especially with a “shim” type alignment because as you change either camber or caster, the other setting is affected. This makes the process very time consuming and some alignment shops will align the car to settings easy for them, rather than the setting you requested.NOTE:for best results, have the alignment shop print out a before and after specification sheet. Third, aligning a classic Ford, especially a pre-1967 car, is not an exact process and, due to the effects that changing either camber or caster have on each other, the alignment shop will need a set of tolerance specifications to align the car within. The following is a print out that I take to my alignment shop every time I have my car aligned.
Please align to these specs “1960-1966 Mustang and Falcon Performance Alignment with or without UCA drop”.
These specifications are in order of importance.