There's always so much debate about the so-called "Mustang II" suspension systems that I figured we should have a thread all about it (STICKY?). Most of the information thrown around is false or unsubstantiated, but there are some good and valid points to be made on both sides. Everyone knows I'm a fan of a good MII IFS in certain applications, and I'll start the ball rolling with my feelings on the subject. It's certainly not the last word, and I'll say some things just as devil's advocate for the sake of the debate.
There's bound to be some good action on the topic, but let's keep it clean and get some good info out there! I want to see arguments presented intelligently, and stories of structural failures should be first-hand or accompanied by evidence.
:SNSign:
Back in the day, drag racers wanted more room in the engine compartment for huge engines, so they started grafting the suspension system from the small Pinto-based Mustang II into the earlier cars. Street rodders wanted to get away from the non-independent I-beam front axle, so they did the same. It actually had great geometry and a compact package, but wasn't really up to the task of daily use in a larger car. Also, since every installation was custom, the quality of workmanship varied greatly. Long story short, in theory they were great, in practice they were so-so, and there were occasional failures.
So, higher-end street rod shops started to design front suspension systems with the advantages of the Mustang II suspension (compact package, great geometry) but with custom-fabricated, extra-beefy (to use an engineering term), components. These are what evolved into the current "Mustang II" suspension package we see today. They don't share a single component with a Mustang II suspension, but they still carry the name due to their heritage I guess. There's no more strut rod, and no more conventional spring/shock combo. They're now a true SLA (Short/Long Arm) dual A-arm suspension system with coilovers, widely held to be one of the very best front suspension configurations for both ride and handling (see every other suspension thread on here).
Since the resulting package is so compact, the shock towers can be removed from the car altogether. This causes some people to state that the front frame rails are now being loaded in a way contrary to how they were designed -- carrying the full weight of the front end. The claim is that the load is normally applied at the top of the shock tower and carried back to the firewall somehow. At first glance this seems to make sense, but it's only partially true. The load is indeed applied at the top of the shock tower, but the thin sheet metal between the shock tower and the firewall doesn't carry the load. The bracing that runs between the top of the shock towers and the center of the firewall carries a little, but it's mainly there to keep the shock towers from settling towards each other, since there's a large twisting force around the frame rails due to the application of the suspension force at such a distance. Leave that bracing off for a while and to replace it you'll need a hydraulic ram to spread the shock towers back apart.
In reality, the suspension load applied to the top of the shock tower is carried by the shock tower down to -- you guessed it -- the frame rails. The load goes into the shock tower and the shock tower is mounted to the frame rail. The frame rails support the vast majority of the load regardless of whether the shock towers are present or not.
Modern "Mustang II" suspension systems reinforce the frame rails with steel plate, and then tie the two sides together with a very substantial crossmember. There is much more load sharing between the two sides than with the stock suspension, and a much more rigid connection between the two sides.
Due to the much higher performance of modern brakes over the stock ones, it's a good idea to reinforce the front end, regardless of the type of suspension, to better handle these loads. With shock towers, one uses heavier bracing between the towers and the cowl as well as bracing from one tower to the other. Without shock towers, it's good to run support from the front of the front frame rails up and back to the upper cowl. The two sides are already rigidly braced together by the crossmember.
So, it could be argued that a good Mustang II-type suspension system is actually structurally superior to the stock configuration, since the loads are carried by the frame rails in a similar way and the two sides are connected in a far better way.
As icing on the cake, you get a huge engine compartment for that big block, DOHC mod motor, or big-tube custom headers.
As extra icing, you get front-steer rack & pinion steering so there's even more room for headers, clutch linkage, or whatever.
And as the cherry on top, if you or a buddy are a good welder you can't beat the price!
Go nuts.
There's bound to be some good action on the topic, but let's keep it clean and get some good info out there! I want to see arguments presented intelligently, and stories of structural failures should be first-hand or accompanied by evidence.
:SNSign:
Back in the day, drag racers wanted more room in the engine compartment for huge engines, so they started grafting the suspension system from the small Pinto-based Mustang II into the earlier cars. Street rodders wanted to get away from the non-independent I-beam front axle, so they did the same. It actually had great geometry and a compact package, but wasn't really up to the task of daily use in a larger car. Also, since every installation was custom, the quality of workmanship varied greatly. Long story short, in theory they were great, in practice they were so-so, and there were occasional failures.
So, higher-end street rod shops started to design front suspension systems with the advantages of the Mustang II suspension (compact package, great geometry) but with custom-fabricated, extra-beefy (to use an engineering term), components. These are what evolved into the current "Mustang II" suspension package we see today. They don't share a single component with a Mustang II suspension, but they still carry the name due to their heritage I guess. There's no more strut rod, and no more conventional spring/shock combo. They're now a true SLA (Short/Long Arm) dual A-arm suspension system with coilovers, widely held to be one of the very best front suspension configurations for both ride and handling (see every other suspension thread on here).
Since the resulting package is so compact, the shock towers can be removed from the car altogether. This causes some people to state that the front frame rails are now being loaded in a way contrary to how they were designed -- carrying the full weight of the front end. The claim is that the load is normally applied at the top of the shock tower and carried back to the firewall somehow. At first glance this seems to make sense, but it's only partially true. The load is indeed applied at the top of the shock tower, but the thin sheet metal between the shock tower and the firewall doesn't carry the load. The bracing that runs between the top of the shock towers and the center of the firewall carries a little, but it's mainly there to keep the shock towers from settling towards each other, since there's a large twisting force around the frame rails due to the application of the suspension force at such a distance. Leave that bracing off for a while and to replace it you'll need a hydraulic ram to spread the shock towers back apart.
In reality, the suspension load applied to the top of the shock tower is carried by the shock tower down to -- you guessed it -- the frame rails. The load goes into the shock tower and the shock tower is mounted to the frame rail. The frame rails support the vast majority of the load regardless of whether the shock towers are present or not.
Modern "Mustang II" suspension systems reinforce the frame rails with steel plate, and then tie the two sides together with a very substantial crossmember. There is much more load sharing between the two sides than with the stock suspension, and a much more rigid connection between the two sides.
Due to the much higher performance of modern brakes over the stock ones, it's a good idea to reinforce the front end, regardless of the type of suspension, to better handle these loads. With shock towers, one uses heavier bracing between the towers and the cowl as well as bracing from one tower to the other. Without shock towers, it's good to run support from the front of the front frame rails up and back to the upper cowl. The two sides are already rigidly braced together by the crossmember.
So, it could be argued that a good Mustang II-type suspension system is actually structurally superior to the stock configuration, since the loads are carried by the frame rails in a similar way and the two sides are connected in a far better way.
As icing on the cake, you get a huge engine compartment for that big block, DOHC mod motor, or big-tube custom headers.
As extra icing, you get front-steer rack & pinion steering so there's even more room for headers, clutch linkage, or whatever.
And as the cherry on top, if you or a buddy are a good welder you can't beat the price!
Go nuts.
