How The Original Ford Mustang’s Suspension Worked: Suspension Secrets

The first generation Ford Mustang was the start of one of the most iconic nameplates in automotive history. Introduced part way through the 1964 model year as a 1965 model, the Mustang quickly became a top seller for Ford. During its first half year of production in 1964, Ford sold over 121,000 Mustangs followed by almost 560,000 in 1965. The model was so successful, in fact, that it spawned an entire new class of cars called “Pony cars.” Both Chrysler and GM would follow in 1966 and 1967 respectively with their own pony cars – the Dodge Charger and the Chevrolet Camaro/Pontiac Firebird. But the Mustang would remain a sales king for many years to come; in fact, it’s still the King of the Hill among sport coupes. Given the Mustang’s status in auto history, it only made sense for us to include it in Suspension Secrets, our regular deep-dive into the suspensions of some of the world’s most iconic cars. Let’s get into it.

Baby Boomers

The Mustang was developed in the early ’60’s as a result of Lee Iacocca, then Vice President and General Manager of Ford, wanting to tap into the baby boomers who were coming of age. Many were college educated, and Ford’s research showed that these customers bought cars at a much higher rate than others, and they wanted something fun and sporty. Still, Boomers weren’t flush with cash, so the car had to be reasonably priced. This meant keeping costs down and using as many existing parts as possible.

The team quickly determined that the unibody Falcon, a small coupe (though it could be had as a sedan or wagon, too) would be the right car to start from. It was a fairly new platform, was the right size, and could accommodate the desired engine choices. The resulting Mustang was a vehicle that had a very common suspension layout for the time with a solid rear axle and a double wishbone in the front.

Double Wishbone Front

While the front suspension can definitely be called a double wishbone, there are some aspects of it that are quite unique.

The lower wishbone is not really a wishbone, as such, but is actually made of two parts – the lower arm and a strut. The parts are held together with two bolts, and are connected to the body with rubber isolators and bushings. Since the connection between the two components is rigid, the arm and strut work together to act like a wishbone.

The upper arm looks much more like a traditional wishbone, but that’s where the similarities end. The connection between each arm and the body is via two metal-to-metal pivots. There are no rubber bushings here. These pivots must be regularly greased to keep them from wearing out and do little to isolate the car from road noise and impact harshness. These early Mustangs were not cushy or quiet.

The other aspect of the upper arms that is unusual is a result of how the spring is mounted.

Spring Mounting

Traditionally, even in the early sixties, the springs in a double wishbone suspension would be attached to the lower arm either by sitting on the arm directly, or as part of a spring/damper strut assembly.

Here you see a 1965 Ford Galaxie 500 front suspension with a very similar lower arm and strut arrangement as the Mustang has but the spring is sitting on the lower arm.

In the Mustang, however, the spring is mounted on the upper arm and sits on a small pivot so the spring doesn’t have to bow as the arm swings up and down. This explains why Ford used metal to metal pivots instead of bushings in the upper arm. The pressure of the spring would be too great for the rubber to handle, and they wouldn’t last very long.

I don’t know why Ford put the spring on the upper arm like this, but I did hear an interesting story many years ago. According to legend, the Falcon platform was originally developed to be front wheel drive, but this was changed over the years until it finally entered production as rear wheel drive. By the time the decision was made to ditch front wheel drive, the design had already matured with the spring on the upper arm in order to keep it out of the way of a driveshaft. I don’t know if this story is true but looking at the design, it does make some sense. If anyone knows more about this, I would love to hear about it.

‘Hotchkiss’ Rear Suspension

The rear suspension in the Mustang is a much more traditional design found in many cars of that era. It uses a solid axle held on by two leaf springs. Known as a Hotchkiss suspension, it is a very simple design still used in many pickup trucks today as well as in plenty of pre-2000 Jeeps.

There are no links or control arms in a Hotchkiss suspension, the leaf springs do it all. They hold the axle in place, keep it located fore and aft as well a side to side, and they act as the springs by flexing up and down.

via GIPHY

The big difference between a modern pickup truck Hotchkiss and the one in the 1966 Mustang is the location of the dampers. In the Mustang the left and right dampers are both attached to the front side of the axle while in a modern truck setup one will be mounted on the front side while the other on the back side of the axle. This is called a staggered shock arrangement, and it is done to combat axle hop.

As you apply forward engine torque to a Hotchkiss suspension, the wheels will of course want to rotate in the forward direction. At the same time, the axle housing itself will want to rotate in a rearward direction as a reaction to that torque. Since the only thing holding the axle in place are the two leaf springs and since these springs are relatively flexible, the reaction torque forces them into an “S” shape.

This is called axle wind-up. If the tires stay hooked up to the pavement while this is happening, all will be fine, but if you have a lot of engine torque or if the road is a bit slippery from rain or leaves, then the tires may lose traction. When they do, the springs will snap back to being straight. When the tires regain traction, the whole process starts over again. In bad cases, this cycle can happen several times per second and cause a violent shaking in the car.

If the dampers are both mounted either on the front or back side of the axle, the axle rotation during wind-up happens along a line between the bottoms of the two dampers. If, on the other hand, we place one damper in front of the axle and the other behind, the wind-up would force one or both dampers to stroke which would add damping to the wind-up and help stop it.

In 1965, this problem wasn’t such a big deal since engines weren’t yet very powerful but as engines got bigger and stronger, especially in cars like the Mustang, axle hop became a much bigger problem. Hot rodders of the day quickly learned to use traction bars like these:

…to help stop the wind-up and the resulting axle hop.

Ford stuck with the Falcon platform for the Mustang until the Mustang II arrived in 1974, racking up several million in sales in the process. In spite of some of the issues this platform had, there is no arguing that this represents a supremely successful design which is still revered today.

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