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Why Upgrade Your Mustang's Upper & Lower Control Arms

Written By: Josh Honeycutt

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Take control of your Mustang's handling and replace the weak and flexible stock control arms with a performance minded aftermarket set. Fine-tuning your Mustang's suspension is made easy with the quick to install, bolt-on performance options for both upper and lower control arms.

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If you're looking to spice up your Mustang suspension, aftermarket control arms can give your Mustang a tighter feel. This guide will show you the benefits as well as the disadvantages to upgrading from stock control arms.

What are Mustang Control Arms?

The front arms eliminate any pinion angle deflection that can botch traction while the rears restrain the axle from moving front and back, just as the leaf springs on older model vehicles and most trucks. Rear control arms bolt up to the upper part of the differential housing and connect to the body. Their main purpose is to support the up and down movement of the axles. The lower control arms also transmit the force from the wheels to the chassis. Of course, control arms are much lighter, and more effective in preventing axle wrap than the traditional leaf spring set up.

Under normal driving conditions the factory arms are okay, but if you enjoy taking turns, occasionally hitting the track, or just want that extra peace of mind on the road, then upgrading the Mustang’s control arms is highly recommended.

Red SN95 1999-2004 Mustang on the Road

What is Axle Wrapping/Binding?

For those who don’t know, axle wrap is torque and traction combining to twist the axle (pushing the nose of the differential up going forward and down going backward) into an "S" shape. The energy is stored in the spring until the tire slips, and at that point the spring snaps back violently. Sometimes this results in a hopping sensation, hence the other common term, "axle hop." It can be very hard on driveshafts and u-joints.

Lakewood Performance U-Joint for 1996-2004 and 1997-1995 5.0L Manual Mustangs

Weaknesses in a Mustang's Stock Control Arms

Although a significant improvement over leaf springs, control arms has some downfalls in its stock form. Ford used a soft rubber bushing at the mounting points at the chassis and axle. This allows for a more comfortable, forgiving riding experience for the average driver but poor performance in the way of handling and traction.

The factory pieces are a stamped steel design and, along with the bushings, allow the suspension to be incredibly flexible. As one portion of the chassis moves upward another part can move downward, which occurs during higher speed turns (body roll). This design leaves a lot to be desired in the rigidity area, allowing for wheel hop off the line and side-to-side movement of the axle during aggressive turns—all of which are not desirable, but can be corrected.

Msutang Lower Rear Control Arms Labeled

Choosing Aftermarket Control Arms for Your Mustang

There are many aftermarket suspension options for today’s Mustang owner. Many of them are high quality tubular steel pieces with high-grade tig or mig welded seams, providing added rigidity and support. The tubular design is much more rigid than the stock stamped steel piece and in most cases, lighter. If tracks days are every day for your Mustang consider tubular arms, but if your Mustang is a daily a boxed design will do just fine. 

The two most popular choices are adjustable and fixed control arms. Both can be used on a stock Mustang. However, if the car is lowered the adjustable control arms must be used to set the proper angle. Adjustable arms allow you to adjust your pinion angle in a matter of minutes, something we'll explore more further down.

Adjsutable BMR Suspension Mustang Control Arm
Adjsutable Control Arm

Rubber vs. Polyurethane Bushings

A lot of the kits available are offered with solid polyurethane or spherical end bushings (spherical bushings allow for slightly better handling). Both of these are a huge improvement over the soft rubber stock bushings. Rubber and poly-urethane bushings still allow the suspension to bind under harsh conditions (although to a lesser degree than stock), but they will add some comfort and predictability to your Mustang.

Prothane Mustang Suspension Bushings
Polyurethane Bushing Set

What are Spherical Ends?

Instead of using a big bushing, spherical ends (also referred to as Heim joints) use a small metal ball that pivots inside the joint. This allows the control arm to move multiple directions simultaneously. This style end also eliminates some axle binding. Spherical ends are recommended to someone looking to get the most out of their Mustang at the track. All of these designs are adjustable as well.

A couple of products also offer an adjustable spring perch. This allows you to adjust the ride height in the rear of the car with ease. It allows you to lower the rear of the car up to one inch or raise it by two inches. Having this adjustment lets you further fine tune your suspension for perfect launches and will even allow you to fit in a taller tire for certain applications.

Spherical Mustang Control Arm Ends from SR Performance
Spherical Control Arm Ends

What Issues do Aftermarket Control Arms Fix?

  • Improve 60 ft. launch times
  • Keep your rear tires more planted allowing for improved traction and handling
  • Stronger construction that can handle more abuse than OEM parts
  • Fixes arc of travel
  • Prevents binding

Control arm upgrades are meant to maximize the handling characteristics of the Mustang by strengthening the car’s suspension components. This is achieved by utilizing stronger materials, as well as superior designs over the factory components. Obviously, there are different types of control arms, upper and lower, as well as fixed or adjustable to take into account when upgrading. Upgrading the control arms on your Mustang will help with traction and control by keeping your tires where they belong…on the ground.

J&M Control Arm Installed
Aftermarket Control Arm Installed

When you take a hard turn the stock upper control arms are notorious for binding which makes handling unpredictable. Binding is when the axle winds up or twists unaccordingly to the body of the car. This also prevents your tires from achieving complete traction. This is also a leading cause of snap over-steering. Snap over-steering occurs when the vehicle transfers weight during a turn and unexpectedly snaps in the opposite direction due to binding. It's extremely hard for a driver to correct, not to mention highly dangerous. Upgrading to a good set of upper control arms will give you faster launches, lower 60 foot times, improve handling, and tighten up the suspension by preventing snap oversteer.

2000 GT Mustang at the Track

Benefits of Adjustable vs. Non-Adjustable Suspension

There are benefits and drawbacks to using adjustable control arms rather than non-adjustable. While both perform exceptionally well, non-adjustables have 0 room for manipulation. Non-adjustables work fantastic on cars at stock ride height, but are simply looking for a little more traction. However, if a Mustang is lowered, having adjustable control arms becomes much more important.

As mentioned earlier, they allow for the correct adjustment of the pinion angle on the driveshaft. The pinion angle needs to be adjusted when lowered, something a non-adjustable can’t complete. This not only will provide more traction with the correct angle, but also increase longevity by maintaining proper wear and tear on seals and the drivetrain as a whole. Without the proper geometry, you're looking at the potential of damaging your driveshaft's u-joints. 

J&M Fixed Rear Upper Mustang Control Arm Installed
Fixed Rear Upper Control Arm Installed

The Downside to Aftermarket Mustang Control Arms

While increasing launching capability, there are a few downsides to be aware of. First, anything aftermarket isn’t free. Secondly, with a stiffer rear suspension the driver will feel some of those small road bumps and vibrations that would normally go unnoticed.

Control Arm Installation Difficulty

Basic hand tools, a jack, jack stands, wheel chocks, and a torque wrench that can handle 150-200 ft-lbs will handle the job. One of the trickier areas is separating the ball joints from the knuckle (when doing the front arms). You'll either have to muscle them out with a prybar (which can be tricky in the best of circumstances) or rent a pickle fork from your local parts shop. Torquing the bolts down to the necessary specs can also be a pain considering how high than can get to. Assuming you have access to all of the right tools and have the mechanical understanding, expect control arms to take you a few hours. Something to consider for lower arms is changing any part that affects the spring can be extremely dangerous if it is not done properly.

1994-1998 Mustang without the Tire

Key Takeaway

If you want your Mustang to excel at straight line driving, track racing, or drifting then the aftermarket control arms are the only option. They’ll reduce wheel hop and the wasted movement of axle rotation while enhancing your handling and feel. If you’re more concerned with ride comfort and not feeling all of the bumps and potholes, sticking with stock might work for you.

Alternatives to Aftermarket Control Arms

To truly get the most out of your Mustang’s suspension, I would recommend going a step above a new set of control arms. A panhard bar or a watts link are two designs that answer many of the problems associated with a 4-link suspension by providing added stiffness and support. Panhard bars didn’t come standard on Mustangs until the year 2005, but were introduced to prevent many of the issues Mustang owners had complained about in previous model years.

Both of these designs center the rear axle with the middle of the car to help prevent axle binding or unwanted lateral movement. Considering the poor design of the factory lower control arms, a panhard bar or a watts link will reduce body roll and give you added traction when cornering.

Adjustable Mustang Panhard Bar
Adjustable Panhard Bar
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