What Is A Mustang II Suspension And How To Measure For Shocks

Mustang II front suspension has become a go-to conversion for many hotrodders, whether they’re pulling the front end out of the junkyard or swapping in a fabricated aftermarket setup. The Ford Mustang II was one of the first affordable rigs to come from the factory with components that are now the standard in performance vehicles. This includes rack-and-pinion steering, front-steer spindles and disc brakes—even on base models.

On top of all that, we’re still talking about a Mustang. That means it was a popular enough platform—yes, even this generation—to find a huge assortment of Mustang II parts in the wild. It’s easy to track down spindles, brake options and steering racks, whether you want junkyard gold or shiny new stuff from your favorite speed shop.

It’s no surprise that many people saw opportunities to graft this front end into their own rides. It provides a big leap in drivability and stopping power compared to vehicles with old-school steering boxes and drum brake spindles.

WHATS THE DIFFERENCE BETWEEN A STOCK MUSTANG II FRONT END AND AFTERMARKET VERSIONS?

As the stock swap gained popularity over the years, many aftermarket manufacturers used the Mustang II front suspension as the basis for their own weld-in swaps. But that doesn’t make them the exact same.

First of all, the stock version has one set of dimensions. All Ford Mustang II cars, from 1974-1978, came with the same crossmember, control arms, spring pocket, rack-and-pinion, etc. That’s why our QA1 direct-fit Mustang II coil-over shocks fit those cars without any modification.

On the flip side, aftermarket Mustang II front suspension systems come in different shapes and sizes. They often use a similar shock mount on the lower control arm and incorporate a Mustang II spindle. But other aspects vary from kit to kit. The most common differences we see are the pickup points for the control arms and the spring pocket location.

The factory Ford Mustang II front suspension has very little travel. That means you can use a short shock. However, many aftermarket systems change the location of that spring pocket. This gives you more suspension travel, which is a good thing. But it also means coil-overs meant to fit a stock Mustang II front suspension will be too short. You won’t be able to achieve the ride height you want because you can’t add an extension to the machined upper stud mount of our bolt-in Mustang II coilovers.

But the length isn’t the only difference. Some aftermarket Mustang II front ends use a different mounting configuration for their shocks. It’s not uncommon to see shock mounts that require an eyelet on the upper mount, trading the stud-mount coil-over for an eyelet-to-eyelet style shock. This is another instance where our direct-fit Mustang II coil-overs would not fit. 

HOW DO I MEASURE MY VEHICLE TO GET THE RIGHT COILOVER SHOCKS AND SPRINGS?

1. Identify If Your Suspension is Mustang II or Aftermarket Tubular Components

First, we want to be sure we know what we’re working with. If you've bought a vehicle and were told it had a Mustang II suspension, that could mean a range of things. The stock Mustang II crossmember is stamped steel, and the control arms are stamped steel with strut rod lower. If you climb under the car for an inspection and don't see these things, it's likely that aftermarket components were used.

2. Identify Shock Mount Styles And Specs

• Stock mount would have a 7/16” bolt and a 3-3/8” sleeve in the lower, and feature a stud top
  
• Aftermarket can be a stock-style lower, or larger bolts are sometimes used for strength. Different widths of sleeves may be used. The upper shock mount could remove the upper spring pocket entirely in lieu of an eyelet mount designed for an encapsulated coilover.

These specifications will allow us to recommend some specific shocks or sleeves that can get you the closest to being able to bolt up coilovers with minimal customization.

If you have a spring that came out of the vehicle already, it may be useful to measure the inside diameter of it to verify the spring pocket, but these are most usually standard across the stock crossmember and the aftermarket versions.

3. Weigh The Vehicle

It’s sometimes hard to get an accurate weight on a project vehicle, unless its complete and road-ready. However, the more accurate you can be the vehicle weight, the closer we can get to accurate recommendations. You can try reinstalling the stock components temporarily until the weight can be determined. If getting an accurate weight is not possible, some trial and error may be necessary to find the right spring rate for your preferences.

As an additional note about ride height of the vehicle, due to the compact design of the Mustang II suspension, it’s easy to swap the shocks but is not the most flexible design for different ride heights. A longer or shorter shock and spring may get you to desired ride height, but it is easy to push the geometry beyond its limits and start to negatively impact the driving experience. Alignment issues and bump steer are common when the line is crossed, and you don’t want to spent a lot of time and money only to make the vehicle ride worse instead of better.

4. Measure For The Shock

The stock shocks in Mustang II suspension systems were extremely short and have very little stroke, leaving very little room for error if the ride height is altered. Many aftermarket suspensions account for this in their design and require a longer shock.

Set up your suspension at the desired ride height and than make your measurements— this will allow us to find a shock with the best chance of not topping or bottoming out.

5. Measure The Lower Control Arm

With the stock control arms, you can use QA1’s chart for selecting spring rate; aftermarket parts, however, can vary significantly. The measurements of the lower control arm are vital to our calculations, along with the vehicle’s weight, to ensure that we suggest a spring rate that will be accurate the first time.

Imagine a line that goes from the center of the ball joint and goes straight to the frame. Measure from the center of the ball joint to the point the lower control arm pivots at the frame. Now measure from the shock mount to the pivot point at the frame. This tells us the ratio the shock moves versus the wheel and tire, which affects what spring rate is needed.

Common Issues

There a number of common complaints and issues that enthusiasts with Mustang II-style front suspension systems are trying to solve. Often, people are buying cars with the suspension already installed and need to then diagnose and problem-solve. Here are a few examples and important tips:

The ride is too firm

A common complaint is that a very firm spring was used when the car was built. A different powertrain may have been installed and the suspension needs to be addressed to correct for it. This could possibly be the wrong spring rate due to the ride height being so low that the shock bottoms out. A very firm spring stops the bottoming out, but tends to rides harshly.

The ride is too soft

Common issues when experiencing the shocks bottoming out are wheels hitting the inner fenders or the headers/exhaust contacting the ground. This is usually a ride height issue, and while it may look really cool, it is likely at the lowest extreme of the suspension’s capability. A firmer spring may help the situation, but at some point the ride will be much too harsh to be enjoyable. If coilovers are installed, slowly raising the ride height ¼” to ½” at a time may be a good compromise to keep the attitude of the vehicle’s rake and also gett the suspension to a point that makes the vehicle enjoyable to drive.

The ride height too high/low

When Mustang II suspensions are swapped into custom applications, the ride height is greatly determined by how the crossmember was installed. There will be some adjustment with the shock and spring for ride height, but pushing it too far can lead to poor handling and drivability.

There’s an unsteady feeling when driving, like the vehicle is all over the road

Other than the obligatory check of the ball joints and ensuring that the steering components are tight, you’ll want to make sure that he vehicle has a proper alignment done by a reputable shop. If those things have been checked than it is likely that the suspension is being pushed to it’s limit and a ride height change may help.