This is what I have learned over the years and would like to share with Mustang/Cougar folks who want to make their cars handle
I am still in the process of building this page so things are going to be edited and more info on setting up suspension, alignment specs and braking systems will be added.
Polyurethane is fine for sway bar brackets and top insulators on coil springs but I'd avoid using them on strut rods. A strut rods needs to have motion where it mounts through the front frame bracket, so that it can follow the swing arc of the lower control arm. When replacing rubber with polyurethane, it is like clamping the strut rod to the frame bracket with a solid block. Now, motion imposed by the lower control arm, tries to bend the rod behind the bushing, which resist being flexed. This puts a significantly larger stress load on the rod right where the threads for the adjuster nut already act as a stress riser. This fatigue failure and subsequent breakage, could lead to loss of control of the car.
If you want to improve the performance of strut rods, you can get rubber bushings from Global West, that are of a higher durometer (density) than stock, but without being too solid. For people with higher performance in mind, Global West also has a heim jointed strut rod assembly, that mounts in the stock location with no modifications to the car's chassis.
Lower control arm bushings, spring perches and leaf spring bushings are also not a good place for polyurethane. The factory rubber bushings at these locations are pressed tightly into their bores (lower arm, spring perch,leaf spring eylets) and the center bolts tightly clamp the inner steel sleeve of these bushings, meaning that neither of these points rotates where clamped or pressed. Where the motion comes from in these joints is in the torsional flex of the rubber bushing itself. For example if you raise your car and disconnect the spindle from the lower control arm and leave the bolt tight at the arm's pivot bushing and then rotate the arm each direction it will want to snap back to its relaxed position in the center, because you are just flexing the bushing back and forth in torsion. Now when you replace any of these bushings with a hard poly bushing that has virtually no torsional flex, you are asking either the outer diameter to rotate in the control arm sleeve, or for the inner diameter to rotate on the steel sleeve that the bolt passes through. The inside and outside diameters of the bushing were not designed as a rotating bearing and removing the torsional flex of a rubber bushing and replacing it with a non flexible polyurethane bushing is an un-engineering of the factory's design. That is why poly urethane bushed cars squeak, it's because the bushing holds until something has to give and the cre-e-e-a-a-k you hear is the slipping of a tight bushing in its hole. The factory used this design to cut down on production costs, as machining precision bearings, bushings and sleeves is much more expensive than pouring rubber into a mold. Also since the general public isn't known to maintain their vehicles properly, it eliminated the need for lubrication of these areas.
If rubber doesn't meet your performance needs and a higher durometer (density) rubber bushing is un-available for the application, go with the rollerized shackle kit from Global West and their lower control arms with rollerized (spherical joint) inner mount pivots. Global's Del-a-Lum shackles utilize thick aluminum sleeves with grease grooves and zirk fittings with a nylon bushing inside them that acts as a true un-bound bearing that is completely free to rotate, allowing the leaf spring to travel bind free. They also do some of the work of a panhard rod as they have no lateral slop and thus control sideways axle movement in the car. The lower control arms have sherical ball joints installed at the frame pivot point that allow them to rotate freely with no slop or flex. The precision nature of this steel spherical joint allows the lower control arm to resist moving inboard under hard cornering loads due to bushing flex, thus maintaining a more accurate camber angle through the corner and better tire contact with the pavement. Cobra Automotive uses a bushing design similar to the Global West shackles on spring perches. These will long outlive rubber or polyurethane bushings and eliminate torsional bind found in the stock rubber bushing design. Anyone who has installed reproduction spring perches and then found out that the bushings are worn out in 2 years and the perches have walked on the shafts to the point that they are rubbing on the control arms, will be able to appreciate rollerized perches.
Another design flaw of polyurethane bushings is that they compress under the cars weight. Since they have no elastic qualities, they don't regain their original shape. This results in a gradual ovalizing of the inner hole that rides on the center mounting bolt, thus the bushing becomes sloppy. There are a lot of companies making a lot of money manufacturing cheap poly bushings and selling them for a good markup. They know that since this design isn't a permanent fix that you will need to come back to them when they wear out. When a magazine journalist visited Global West, he said, "you have a great bunch of products here, but most of our advertisers are in the market for making REPLACEMENT parts and your parts dont look like they need much replacing." That's why you see more articles on poly bushing installations and less articles on Global West products installations.
SUSPENSION ARM RELOCATION & GEOMETRY:
When Shelby relocated upper control arms, people assumed it was to lower the car.
The intention was twofold; to improve the car's roll center geometry and to improve negative camber generation. Look at your car head on and imagine drawing a line through the length of the upper arm and continuing this line on through toward the other side of the car. Now do the same for the lower arm. Since the lower arm is somewhat close to parallel to the ground but the upper arm slopes downward toward the shock tower, you can see that in drawing these two lines, they will intersect at a point toward the other side of the car. Now do this for the arms of the other side of the car. Take the point where these lines intersect and draw a line from there to the middle of the opposite tire where it interfaces with the ground. Do this to both sides. These final two lines will cross each other like an X and the middle of the X where these two lines cross one another, is the imaginary roll center point of the car. Changing the slope of the upper arm affects where the center lines of the upper arm and lower arm will cross and this will raise or lower where the lines to the middle of the tires will cross. Shelby Enterprises moved the roll center point by lowering the upper arms 1". Global West has improved the geometry further by lowering the arms 1-3/8". This required a re-alignment of the upper ball joint mounting point.
Now let's move on to camber curve. Picture what happens when you swing the control arm through its arc. As you rotate the arm upward, the ball joint end moves inward toward the shock tower. This shortening effect of the upper arm is what tilts the spindle and thus the tire inboard at the top, producing negative camber. The longer the arm is, the wider a radius it swings through, thus the shortening of the arm is reduced for a given amount of swing. Now do the opposite and shorten the arm. The arm will swing through a sharper radius and have a faster shortening effect in a given amount of travel. Global West has shortened the stock length of the arms to increase the generation of negative camber in a given amount of travel. This shortening effect of the arm increases exponentially as you raise the it closer to vertical. So each increment of travel in the arm's arc results in an exponential shortening thus an ever increasing amount of negative camber as the suspension compresses. This is referred to as the camber curve. Setting the suspension's inital ride height allows you to use the optimal portion of the suspension travel, to take advantage of the best camber curve. This is part of why it is counter productive to over lower a car. You reach a point of diminishing returns as you trade the good geometry and camber curve of this optimized travel range for lowering the cars center of gravity. This of course is on top of the fact that our roads aren't perfect and you need the car to be driveable.
Roll center geometry and camber curve improvements are major factors that make newer cars handle and ride so well. Improving these designs is a way to update older car's handling characteristics to modern car standards. Now that you have improved the tire's contact with the pavement in all conditions, you have gained your handling through increased traction. Since public roads are not smooth and perfect like a race track, you can now use lighter spring rates. This creates a more compliant suspension, which improves the ability of the tires to follow the contours of the road. This also allows the use of a lighter sway bar which reduces the tendency of locking out the independent nature of the suspension. This results in a better balanced and tuned suspension because the foundation of handling, which is improving surface grip of the tire to the road is addressed, rather than throwing parts at the car to make up for its poor traction problems.
Global West has now added a coil over feature to their negative roll system. What makes the coil over kit interesting is that with a reduced diameter spring, there is more clearance of the spring to the inner wall of the tire so you can move the mounting point further out on the arm without hitting the tire. This is an issue that race suspension designers have always tried to optimize. The further you mount the spring inboard on the control arm, the less effective it is. Have you ever jacked a car up by the control arm and your jack is about at the mid point or less on the arm and you notice that the suspension barely compresses despite the fact that the tire is off of the ground? On top of improving the load geometry of the spring and arm, this will create more clearance for guys that want to do the BOSS 429 style shocktower notching.
The shafts are bushed with high strength nylon bushings into aluminum housings with grease grooves and grease zerks. This is a vast improvement over the stock shaft design where the shafts are screwed into threaded end caps as a metal on metal joint. Tubular design construction and the addition of cross braces near the shaft make these arms very rigid. Because Global West has optimized the length of the arms, they are of a fixed length design rather than being adjustable. Adjustable arms give the consumer license to upset the camber curve. Global West's lower control arms have a more substantial joining of the inner mounting pivot to the arm compared to the heim joint design used by the competition. Also, the "Nova bearing" inner pivot is much larger in diameter than traditional heim joints thus increasing surface area for better wear and rigidity.
Now that we have improved traction, we have increased the ability to load the control arms. With a rigid upper arm and shaft design, increased traction (especially with sticky race tires) we now are using the upper arm like a can opener on the relatively weak shock tower. This is one of the reasons Ford went to the wrap around gussets like you see on 69-70 boss and big block Mustangs, and on all 69-70 Cougars. This was to distribute the loads of the upper arm on that small gusset plate over a larger surface area. Also part of the design idea, was to spot weld the gusset plate to the shocktower in more than one plane while introducing compound curves to stabilize it and lower the stress loads on the original spot welds. This took care of the famous cracking shock towers. I designed and installed shocktower re-enforcements on a number of cars with high performance suspensions and on cars that had crack repairs where I didn't want them to crack again at the welds. I have the cad drawings done and am going to have a production run done by this spring. These reinforcements will distribute the upper arm stress loads over a larger surface area of the shocktower and into a larger footprint on the subframe-rail.
REAR SUSPENSION LEAF SPRINGS:
Remove the isobushings and solid mount the axle to the springs. Also, do not use any kind of shocks that support the weight of the car, such as air shocks. I have removed cracked floor-pan/shock-mount assemblies from the backs of Cougars and Mustangs (welding and fabrication required) which required finding a donor car to cut a new one out of for a replacement. The factory shock mounts, both in the body and on the springs, were never designed to carry a load, they are only supposed to dampen the load carried by the springs. Load carrying shocks transfer the cars weight off of the wide stance of the leaf springs and instead support this weight on the narrow spacing of the shock mounts. This destabilizes the handling of the car. It also has a negative effect on braking induces wheel hop, since the springs need to be loaded to operate normally.
In addition to high performance front suspension components, Global West offers rear leaf springs for Mustangs with superior anti wrap-up characteristics balanced with good ride quality. Global used to make Cougar and Fairlane/Torino springs but their current spring vendor will no longer do small production runs.
On my last Cougar project, I went to Bett's Springs in Oakland CA and had them manufacture a pair of Cougar springs of my design. I had the front eyelet re-profile to be like a Mustang's standard eyelet instead of the mideye Cougar design. This way I could run the second leaf all the way under the main leaf's front eyelet, therefore supporting the cars load by two leafs under the frame mounting bolt (see attached picture). This, along with proper leaf length and thickness dimensions, has a dramatic effect on combating wrap-up. In essence, traction bars are a "bandaid" for an inadequately designed leafspring.
Many people use Magna's 4-1/2 leaf spring (now called Grab-A-Track), but I don�t like this design. Magna places the half leaf (rebound leaf) on top of the upward-bowing main leaf and they rely on the small metal bands holding the leafs together to create a laminate strength between the two to resist wrap up. When the springs bow upwards as torque is applied, you want to resist this lifting by placing the reinforcing (2nd) leaf under the main leaf and let the wrap up forces lift these two leafs together into the resistance of the frame mounting bolt.
I had the front end ride height and rake that I liked on a peviously built car, so I raised that car and placed the rear axle and front subframes on jackstands to load the suspension to ride height. Then I made a cardboard template measurement of the spring's loaded arc. I weighed the rear wheels of the car that the new springs will go on, at a truck scale next door. I took the loaded arc measurement, the car's weight and the anti wrap up front eye design to the manufacturer, where they built me a spring with a 133 pound rate. Desired ride height in combination with the car's weight, determine what the rate will be.
In the pictures, compare the eyelet design and extra support of the 2nd leaf under the main leaf to the Magna 4 and a half leaf in the other pic. You can see that no matter how many top leafs you stack (called a rebound leaf), you still have only one leaf at the last 1" or so before the eyelet which is where you want to beef things up for anti wrap up.
BIG BRAKE UPGRADE:
A master cylinder with the correct bore diameter will bring out the uptapped potential in your brakes. I had seen that vintage race cars with large front calipers run a 1-1/4" bore master from a mid 1970's F-350 truck and decided to try this out. I was concerned that the bore size would result in poor modulation, but I was very pleased with the results. The pedal is up high and firm but with very good modulation, its the best feel I've ever had out of a manual disc brake car. I was also very happy that the fitting port sizes on the master, and their locations were correct so that I could run the factory brake lines to the factory distribution block on '68 manual brake Mustangs and '67-'68 manual brake Cougars (with early 4 piston caliper type distribution blocks) with no brake line modifications.
The unit I used was from http://www.mustangsplus.com/Merchan...tegory_Code=brk
and sold as the Granada/Versaille/Monarch 4 wheel disc conversion master, part #1740.
If you don't have rear discs, call and ask them if a 1-1/4" bore master can be had with the residual pressures set up for a disc-drum car. The trucks didn't have rear discs in those years as far as I know, so I would think that this is possible. The compatibility issue between master cylinder and disc/drum brakes, is that you need to maintain the correct residual line pressure for discs (about 2 pounds) verses drums (10 pounds). This keeps the proper pre-load on the drum's many linkage points so that brake application is immediate. Drum systems higher residual pressure will make a caliper drag its pads too hard on the rotor. Residual valves also can be installed in line on the brake lines separate of the master cylinder for easy removal/replacement in the future. Of course, on a 4 wheel disc car, residual pressure is the same, front and rear. On the last car I built with this set up, he had Granada Monarch front spindles, calipers and hubs with the 1-1/4" bore master, the stock brake distriubtion block, a Ford Explorer rear disc kit on a Currie Enterprise rear end and no proportioning valve and the car was perfect. We do have plans though to go up to the 12" front brakes.
Since rear brakes contribute to a small amount of the overall braking, you usually don't feel a very big improvement in from a rear disc conversion alone. If you find that you still want more braking than the factory 11" front brakes offer and you find that the aftermarket kit's upgrades to slotted rotors and high performance pads aren't enough, you will want to upgrade to a 12" brake set up. Converting the front brakes to a larger diameter raises the bar for the whole system and after this upgrade, the addition of rear discs will bring the rear brakes into better balance to the fronts. The improvement in 12" brakes comes from more than a larger pad. The big gain is that a larger circumference passes through the pad per revolution, so this combined with the larger pad, increase surface area exponentially. Also grabbing a larger diameter increases the calipers leverage on the spinning hub/wheel combo. Lastly the size of the vents on those racing rotors speak for them selves as far as passing lot's of cooling air through.
Since the racing days of the late 60's and early 70's teams went to the factory parts bins of the full sized cars and made brackets to adatapt big rotors and caliper from T-birds and Galaxies. What they ended up with looked like over grown 65-67 Mustang/Cougar 4 piston set ups. Early 4 piston disc brakes used the same spindle as the drum car but with a caliper bracket instead of a drum backing plate. The racers did this same thing, but scaled it up. They used a larger shaft 1970 drum spindle and had a larger version of the Kesley Hayes caliper bracket custom machined and installed Galaxie or Thunderbird calipers. Another benefit of the '70 drum spindle is that they have no hole for a caliper bracket mounting bolt. This bolt hole is a stress riser and a point of failure of the spindle.
Cobra Automotive offers a replica of the 12" racing brakes with large vented racing rotors and aluminum hats and a vent hose/backing plate kit. You have to use '70 drum spindles (like the Trans Am and SCCA teams did) but with disc hubs (or Cobrautomotive's aluminum racing hubs) and they supply the calipers and custom brackets to mount them.The kit also comes with shims for centering the calipers to the rotor. The calipers are from Thunderbirds and because they rotated the calipers around to be up front of the spindle, (T-bird calipers were at the rear) they had to swap the left and right calipers to get the bleeder valves back up to the top. They then drilled the threads out of the caliper bodies and now the bolt passes through them and threads into the custom caliper bracket instead.These set ups are particularly desireable to the vintage racers because it keeps the hardware period correct and legal for their racing class. You can also go to Wilwood or Baer brakes, theyre lighter but not as durable or period correct. I also have just found out that Stainless Steel Brakes Corp now makes a 13" conversion with bracket and aluminum calipers I would like to see them in person but imagine them to be very similar to the Baer Claws. These larger brakes create more clearance issues, not just from the diameter increase, but also because the wider caliper body doesnt clear the spokes of some wheels. Your most likely bet for a 16" wheel that will fit is the Vintage 48 from Vintage Wheel Works.