Mustang MonthlyHow To Chassis Suspension
Get Better Handling! Installing Street or Track’s solid-mount strut rods
Solid-mount strut rods have been with us now for well over 15 years, but a lot of information is still unknown about them. And there is also some misinformation about how they work. Generally, most of the things you would do to a race car don’t transfer well to street cars. Most upgrades that make your car handle well also make them ride more harshly, which makes it less desirable to drive regularly. This has always been a tradeoff when you upgrade your Mustang suspension.
The strut rods on the early Mustang chassis have been a source of contention since they were first installed in 1964. Several ideas that arose to fix these strut-rod issues have evolved into the solid-mount strut rods that are currently on the market. Most aftermarket strut rods delete the rubber bushing found on the original Ford units to eliminate movement under braking and cornering. Aftermarket rods also incorporate an adjustable-length design for 1965-66 Mustangs to aid caster settings during alignment.
We went to Shaun Burgess, owner of Street or Track in Michigan, to get their assessment of the strut-rod issues and install a set of its fully adjustable, solid-mount strut rods on our 1965 fastback. Street or Track is earning a reputation for making first-generation Mustangs handle as well as their late-model brethren. In some situations, they surpass them.
Let's go over what the strut rods actually do for the suspension and what the solid-mount and adjustable rods do for a street car. Hopefully, this will clear up any questions on upgrading your strut rods for a better ride.
Strut Rod Defined
There are four general uses for a front strut rod. The first, and most obvious, is to triangulate the mounting of the lower control arm to the body. Ford later eliminated the need for the strut rods when they went to a two-point lower control arm in the Mustang II-style suspension. Newer suspensions also have a control arm with two mounting points. The latest has a reverse-L design.
The second use for a front strut rod was to allow absorption of energy during acceleration and braking. GM actually has a better name for these rods—a brake reaction rod. Under hard braking or acceleration, a car wants to transfer its weight in relation to the center of gravity (inertia). Under hard braking, the car wants to roll over the front tires because the weight wants to continue moving forward, and under hard acceleration wants to put you in the back seat, as you want to stay stationary. The bushings in the strut rods are intended to absorb the energy under these conditions, then return the rod back to its correct position.
The third thing the strut rods do is to smooth out some of the ride harshness of the chassis. When driving on state highways (otherwise known as a Simulated Lunar Surface), the wheel and tire may drop into a dinosaur-extinction-size crater. When that wheel and tire are coming out of the sinkhole, forces on the wheel and tire are pressing the tire towards the back of the car. The bushings in the strut rod are absorbing this impact and dissipating the energy rather than sending it through the chassis of the car, saving your teeth from chattering. The bushings then act to return the suspension back to the original position.
The fourth and final use for strut rods is to adjust the caster on Mustangs made after 1966 to help eliminate the shimming required on the 1965-66 models.
What is Caster?
Caster is the measure of the angle of the steering axis. The caster setting is the angle of the imaginary line that would run through the upper and lower ball joints in relation to the center of the wheel and tire. By angling the steering axis back toward the driver (positive caster), the angle allows for better stability and self-centering of the front wheels.
The best way to think of the effects of caster is the classic bicycle or motorcycle example. A bicycle fork leans back toward the rider to help center the steering and reduce the wandering of the steering. Someone riding a unicycle is riding with zero caster and can turn the wheel very easily in either direction. A unicycle has no centering assistance, and the rider must make these adjustments himself to keep the cycle going forward. A custom chopper with long forks has a lot of caster, and the wheel will want to return to the centered position as the tire casters around the steering axis. A chopper is very hard to steer with an increased turning radius.
The same applies to the caster settings on your car. The more caster in the steering axis, the more stability and the easier the tire will return to the center position. However, as caster increases, the effort to turn the wheel increases and the turning radius is reduced. Some race cars may have caster settings up around 7 degrees, but these cars usually have power assist to help turn the wheels.
1965-66 Suspension Design
The 1965-66 Mustang suspension was a carryover from the Falcon design, which meant the caster and camber were set by shimming the upper control arm out to get the desired alignment numbers. The strut rod was in a fixed point, and with the assembly techniques of the mid-’60s, the strut rod mount position could vary considerably. In 1967, Ford redesigned the suspension to eliminate the shims by installing a cam eccentric on the lower control arm to adjust camber and making the strut rod adjustable to set caster. The struts still relied on rubber bushings to bring the strut rod back to center.
In cases in which the strut-rod bushings are designed to give and return the suspension back into place, it results in a few known problems. The big problem with the strut rod giving in a hard corner or under braking is that the active center on the car moves, and the tires lose grip in a hard corner. In a street car, when you are driving down the road and hit a bump, the strut rod is pulled to the back of the car and the caster is lost temporarily. That means the wheel has difficulty centering itself, and the car wants to jump into the next lane. A lot of people believe this is caused by bumpsteer, but it is actually the poor caster and rod design bouncing you into the next lane.
Recently, we fell in love with polyurethane, and someone got the idea to make strut rod bushings out of polyurethane. The result was a bunch of broken strut rods. Polyurethane does not give like rubber, and the rods were not bending with the movement of the suspension system, causing the solid strut rods to snap. We learned quickly not to use poly bushings in your strut rods, and most houses don't sell them anymore.
Using a rod end gives you full rotation with the suspension movement and up to 30 degrees rotation side to side to assist in misalignment of the strut-rod mounting point. When you change the length of the strut rod, you change the angle of the rod to the mount point and lower control arm. Along with the solid mounting of the rod end, this new design keeps the active center and caster in place on the car, keeping your race car in place and your street car in its lane.
Street or Track Adjustable Strut Rods
We chose the Street or Track units because they are specifically engineered for the 1965-66 chassis. They are not just a bunch of off-the-shelf rod components put together to simplify the product. Street or Track doesn't use a secondary RH/LH adjuster. Adjustment is incorporated into the strut main body, which is custom built. The spindle stop is also incorporated into the rear mounting bracket, eliminating the two-piece design. The rod end is a Teflon-coated unit listed as a service replacement piece. According to Shaun, of all the units they have sold, they haven't sold a replacement rod end for any of those kits. He did replace the ones on his track car after seven years of hard running. Not because they failed, but because the zinc plating was showing some age. His track car doubles as an advertisement, so he went ahead and changed them. Bottom line, a set of solid mount strut rods installed properly are pretty much maintenance free.
Solid-Mount Strut Rods on a Street Car
Installing race suspension components on your street car can make the ride harsh and less desirable to drive. One of the attributes of the spongy strut rod bushings is to absorb impacts of rough road conditions. After removing the bushings on the strut rod, nothing is left to absorb the impact of the potholes found in some regions. All that energy has to be dissipated somewhere and that somewhere is the strut mount and then the frame itself.
We posed this concern to Shaun. “The strut-rod bushings don’t dissipate an appreciable amount of energy,” he says. “You can make an argument there’s a little energy absorption and dissipation due to the damping characteristics of rubber, but not enough to matter. The bushings just function to slow the transmission of force into the bracket, thereby, rounding off the peak force. They have no real effect on energy. Just because the forces transmitted through the strut rods are larger than they would be with a rubber bushing doesn’t mean they automatically demolish the bracket they’re attached to. We've sent out almost 1,200 sets of our strut rods over the last 15 years, and I've never, ever had anybody tear off or crack that mount.”
Installing the Strut Rods
Removing the old strut rods may be the hardest thing to do on the project. Simply put, the older your strut-rod bushings, the harder it might be to remove the old rods. The nuts and inner sleeves will weld themselves in place, and it may take brute force to remove the old strut rods. You won't be using any of it over again, so you don't have to be gentle. Just be careful and don't damage the car at the strut mount or lower control arm.
Safety first! It’s safest to secure the upper control arm while doing the change. Remember the strut rod triangulates the lower control arm, and the force of the spring can cause it to roll out of position. You need to borrow or fabricate a tool to hold the upper control arm in place and relieve the spring pressure. Do not use a 2x4 stuck between the control arm and frame rail. This is very dangerous. You can find the dimensions for the tool in the Ford shop manual for your year car, but it works for all 1965-70 control arms. The car shown here has custom tubular uppers, so we fabricated a bracket to use with the tubular arms.
Installing the new rods is very straightforward. Make sure the bolt holding the rod end is parallel to the floor to allow maximum movement. Using the tool to hold the upper control arm in place and our strut-rod bushings easy to remove, it took us about 45 minutes per side to install the new rods.
One of the biggest mistakes people make, whether upgrading their suspensions or running a stock combination, is running the alignment settings right out of the Ford shop manual or using the settings Shelby from the’60s. Unfortunately, all these original settings were engineered for bias ply tires, not for modern radials. On a lot of blogs, you people state you should run the Shelby G.T. 350 or even the R-alignment specifications, but even these are based on tires and understanding from the ’60s. As far as caster goes, Ford actually specified more caster for a six-cylinder car than they did for the V-8.
These are the optimum settings for use with modern tires:
|OE Ford Spec (V-8)||Shelby Setting||Street or Track|
|Toe-in||1/4 inch||1/8 inch||1/16 inch|
The big difference in the above settings is the more aggressive caster setting with the new strut rods. The increase in caster really helps prevent the car from jumping out of the lane when you hit a bump and reduces wandering. Most aftermarket control arms are now set up for negative camber to help in the corners, and newer, more accurate alignment racks allow tighter toe-in measurements when setting up the alignment.
Helpful Tip: Find a shop that actually knows how to do alignments. A lot of shops have alignment machines, but the computer does the alignment. Most places will tell you if it isn’t in their computer, they can't align it. Seek out shops that do a lot of street rods and unique cars. They usually have someone on staff who actually knows how to align a car.
With our strut rods in place, our first test was the harshness of the solid-mount rod design and my concern about transferring the impacts of the road to the driver. We took our test mule to the nearest railroad track and were pleasantly surprised at the ride quality when hitting bumps. We could tell right away the steering (along with the rack-and-pinion conversion) was slightly firmer than and not as spongy as the factory Ford power steering and strut rods. We could immediately discern much better road feel with the new rods (even testing them before and after with the rack-and-pinion installed). Any additional ride degradation was well offset by the car tracking straight down the road. We had much better control under braking, as well.
Shaun has made a believer out of me with his adjustable solid-mount strut rods. I was really worried about the constant pounding and road harshness while using these rods on a street car, but it isn’t a concern. The benefits far outweigh any negatives with using this race car design on your street car. The design is also well done, not just a bunch of parts cobbled together. And, oh yeah, by building caster adjustment into the rods, your alignment guy will thank you.