FAQs & Tech Tips

MM News

NASA Racers! MM will support NASA road racers with $1,000 contingency prizes for the American Iron, American Iron Extreme, and Spec Iron at the 2019 National Champions. You must register to be eligible.

New! Read the article Maximum Motorsports Tames Fox & SN95 Mustang Rear Suspensions on FordMuscle.com.

MRT Exhaust! MM now offers premium MRT cat-back exhaust systems for 1996-2004 Mustangs.

New! for Street & Strip Mustangs! Big-bore rear wheel cylinders for 1979-1993 Mustang with 9" drum brakes. Improves braking when running big rear tires and front skinnies, and/or different OEM front brakes.

New! Swapping a Coyote into a Fox Mustang? MM's Hydroboost Conversion Kits allow easy installation of a 1996-2004 Mustang Hydroboost power brake assist unit into a 1979-1993 Mustang.

New! Swapping an IRS into your Fox Mustang? MM makes it easier with a brake line kit made just for this conversion. Bolts-in, with no cutting or flaring of brake lines. Designed to fit standard IRS brake hoses.

New! MM's billet aluminum Pedal Box Spacer for Fox Mustangs. Replace the breakage-prone OEM plastic spacer when converting to manual brakes or Hydroboost.

Canadians! Please read the latest about ordering from Canada/shipping to Canada.

We've posted the parts list and link to the video of MM's Mustang in /DRIVE Tuner car Shootout

Eibach Pro-Kit, 2003-04 IRS Cobra HT and Convertible
Actual product may differ from photo.


  • Item # 3594.140
  • Manufacturer: Eibach
Add related IRS items?



Free Shipping on this item!

Eibach Pro-Kit springs for:

  • 2003-2004 Cobra hardtop and convertible with IRS

Eibach Pro-Kit springs:

  • Lower your Mustang for better appearance
  • Increase the spring rate to reduce brake dive and body roll when cornering
  • Lower center of gravity, improving handling
  • Quicken steering response

Ideal for the daily driver, Pro-Kit Springs employ the very same "Hi-Ten" steel and precise tolerances that Eibach uses for its world-famous race springs. With its moderate increase in spring rate above stock, Pro-Kit springs will enhance your driving experience without bone-rattling side effects.

To order

  • Select the discounted MMT-8 to make the install much easier
  • Select the MMPS pinion snubber for better ride quality
  • Select the front and/or rear spring isolators to reduce NVH
  • Click the Add To Cart button

Pro-Kit springs
These are a moderate progressive-rate lowering spring. At ride height, the rate is less than 10% higher than the stock spring rate. However, the progressive design causes the spring rate to increase as the spring compresses, allowing both a lower rate for very good ride quality and a higher rate as the spring compresses to better limit body roll and brake dive. Excellent for daily driving.

Approximate lowering

  • 2003-2004 Cobra hardtop with IRS: (Front: 1.0", Rear: 1.4")
  • 2003-2004 Cobra convertible with IRS: (Front: 1.0", Rear: 1.4")

For best performance and ride quality these springs should be matched with an appropriate set of struts and shocks. Read the Installation tab.

Related products

Eibach Pro-Kit springs will:

  • Lower your Mustang, improving appearance
  • Reduce body roll when cornering and nose-dive when braking, because the spring rate is higher than stock springs
  • Quicken steering response because the spring rate is higher
  • Lower the center of gravity
  • Progressive spring rate
  • Made of premium-quality high-tensile alloy spring wire
  • Powder-coated for long-lasting protection and great looks

Mustangs with solid rear axle only; no Cobra IRS.

  • 2003-2004 Cobra hardtop
  • 2003-2004 Cobra convertible

Does NOT fit

  • Mustang with solid rear axle

While 1979-2004 Mustang front springs can be physically installed in all 1979-2004 Mustangs (except SVO front), the amount of lowering in non-listed applications will not be as expected because of the differences in car weight and initial ride height between years and models.

Installing aftermarket springs involves more than just the spring installation itself. To get the full benefit from your spring purchase, there are several related factors to consider:

Lowering a Mustang changes its front alignment. The relative lack of adjustment features makes it difficult to restore the vehicle to Ford camber specifications without using an aftermarket solution. That's why we created our MM Caster Camber Plates, which greatly extend the range of camber and caster adjustment so you can realign to factory specs.

Spring Isolators
Ford installed rubber isolators on both ends of the springs to reduce NVH (Noise, Vibration, and Harshness). The original rubber isolators deteriorate with age, and compress enough over time to lower your Mustang noticeably. Whenever installing springs, it's best practice to install new spring isolators. Urethane isolators are more durable than rubber, and do not compress appreciably over time.

Struts and Shocks
Ford matched the valving in the original struts and shocks to the original stock spring rates. Most aftermarket springs are stiffer than the stock springs--enough to cause an underdamped situation, meaning the struts and shocks (the dampers) cannot control the springs. That makes the car feel floaty, disconnected from the road, and harder to control. The solution is to install dampers matched to the new, higher spring rates. MM offers a wide variety of quality high-performance dampers. If you'd like help choosing the most appropriate damper for your Mustang, please contact us.

Pinion Snubber
"What's that?" you ask. Ford installed a rubber block above the pinion bearing of the rear end of 8.8" solid-axle equipped 1986-2004 Mustangs. The pinion snubber limited how high the front of the differential could climb as the rear axle rotated during hard acceleration. When hitting large bumps, the axle will typically hit the pinion snubber before it hits the bumpstops. Eibach includes a short pinion snubber with each Pro-Kit.

MM created a pinion snubber that's slightly shorter than stock, but also with a progressive increase in stiffness to improve ride quality. With the MM pinion snubber, the axle hits it less frequently, and when it does, the impact is much less harsh than with the stock snubber or Eibach snubber. Order the MM Pinion Snubber along with Eibach springs and get it at a 20% discount.

Making the Install Easier
Installing front springs in a Mustang used to be a battle. Then MM designed a nifty little tool to ease struggle. Works with aftermarket springs, which have a much shorter free length than stock springs. Fits 1979-2004 Mustangs with stock front control arms. It doesn't work with stock springs because they're too long.

Read the instructions for the spring installation tool.

Do I need to do an alignment after I install springs?
You should always check the alignment after changing your Mustang's ride height. For the stock alignment specs, see your Mustang's factory service manual. For high-performance alignment specs, see the MM caster camber plate instructions, or contact an MM Tech Associate.

Which are the front and rear springs?
Eibach includes printed instructions with each spring set that include information about identifying front and rear springs.

Which end of the spring is the top?
Eibach springs fit just like stock springs. The end of the spring that has been ground flat will be the top for all 1979-2004 Mustang springs, both front and rear, solid axle and IRS.

Do I need to get new isolators?
All aftermarket springs for Mustangs are designed to reuse the factory isolators to prevent premature wear and excessive noise. Look for any protective tubing on the factory springs and take note of its location.

Do I need to modify the bumpstops?
Not unless the information that came with your spring purchase specifies this step.

Do springs ever wear out?
The term "wear out" isn't accurate when applied to springs. The spring rate will never change over time, because rate is determined by the spring wire diameter and the length of the wire before it is wound into a coil. The rate cannot change without physically changing either the wire diameter or its length.

On the other hand, "spring sag" may occur. This means that the spring's free length has changed because its coils are closer together than they were when manufactured. However, this is very unusual with the newest spring steel alloys and modern manufacturing processes used by reputable spring manufacturers. Spring sag has no effect on spring rate, because sag (change in free length) does not change the dimensions of the wire itself. However, the reduced ride height can adversely affect the suspension geometry and cause the suspension to bottom out more frequently.

The majority of ride-height reduction over time is caused by degradation of the spring isolators located at each end of the spring, not from spring sag.

Springs can also break. This is usually due to stress risers on the spring wire, such as pitting caused by corrosion. This is one reason to use spring isolators, as they protect the springs' coating from corrosion.

Will the ride height change if I remove the spring isolators?

I have the MM adjustable rear lower control arms. When I turn the bolt to raise the car, isn't the spring going to compress and change the spring rate?
No. Raising the lower spring perch doesn't change the diameter or length of the spring wire. It simply pushes the spring up, which in turn pushes the car's chassis up. The spring is already compressed from the weight of the car-when you raise the lower spring perch, the car's weight doesn't change enough to affect how much the spring deflects. The spring moves up relative to the ground, which raises the upper spring perch, and therefore the car body.

Where should the bottom end of the front spring be located?
Between the two holes in the control arm spring pocket.

Where should the bottom end of the rear spring be located?
See the MM instructions for installing IRS springs.

Why is there a rubber tube-like thing inside my stock springs?
It's there to reduce NVH (noise-vibration-harshness).

Are Eibach springs progressive?
All Eibach springs are progressive when the application allows it.

How do I know the amount that Eibach springs lowered my Mustang?
Measure your Mustang's ride height before and after installation.

When measuring ride height the most important thing to keep in mind is to be consistent in your technique. For instance, have the same amount of fuel on board. At MM we always fill up the tank immediately before measuring ride height, and set the air pressure of the tires. Park your Mustang in the same level spot. Always measure between the same two points, such as from the ground to the top of the fender opening, or from the wheel lip to the top of the fender opening. Counting how many of your fingers fit into the gap between the top of the tire and the fender lip does NOT qualify as proper measuring.

Do I need to get new isolators and tubing?
All aftermarket springs for Mustangs are designed to reuse factory tubing and isolators to prevent premature wear and excessive noise. Notice any protective tubing on the factory springs and take note of its location for reinstallation.

General Notes

Measure your Mustang's ride height before and after installation. The most important thing is to be consistent in your technique. Have the same amount of fuel on board. At MM we always fill up the tank immediately before measuring ride height, and set the air pressure of the tires. Park your Mustang in the same level spot. Always measure between the same two points. We suggest measuring from the wheel lip to the top of the fender opening. Counting how many of your fingers fit into the gap between the top of the tire and the fender lip is NOT reliable measuring.

With rubber control arm bushings it's important to pre-load the suspension before tightening the suspension pivot bolts. The easiest way to do this is by allowing the full weight of the vehicle to rest on its tires on an alignment rack or ramps. You can also use a lift or jack stands, lifting each suspension corner and tightening all pivot bolts. Correct suspension preload while tightening pivot bolts will result in more consistent lowering, and will greatly extend the life of the rubber pivot bushings. Unlike rubber bushings that twist rather than rotate, urethane bushings and spherical bearings do rotate, and so don't require preloading the suspension while tightening the pivot bolts.

Use the proper spring compressor to remove springs from your car or when disassembling a coil-over strut. Springs store a lot of energy, and can cause serious injury and/or damage if suddenly released.

Take note of the routing and mounting positions of all brake lines, wires, and cables before modifying your suspension. Failing to reinstall the lines in the factory position can cause damage or brake failure.

Before removing springs, label every component from top to bottom with sequential numbers. This will help you reassemble the new and existing parts in their correct order.

Before taking the strut assembly apart, use a marker to draw a vertical line across each component to indicate its original factory orientation. This will help you reinstall all the OE parts correctly.

Mark the position of all alignment-related mounting bolts to provide a good starting point for the post-installation alignment.

Work on one corner of the car at a time. Strut assemblies have parts that must be assembled exactly in factory order. If you make a mistake or lose track, you can refer to the other assembly.

Reinstall all bolts in the same orientation (i.e., up or down) as they were installed originally.

All aftermarket replacement springs for Mustangs are designed to reuse factory tubing and isolators to prevent premature wear and excessive noise. Notice any protective tubing on the factory springs and take note of its location.

Don't let the spindle or brake caliper hang from the brake line, as it can damage the line and cause premature wear or even failure.

To help prevent spring noise on rough roads, leave a 1/4" - 1/2" space between the end of the coil and the end of the spring seat pocket.

Spring isolators reduce the transmission of road noise into the passenger compartment. Age alone will deteriorate rubber isolators as much or more than mileage does. Replace the isolators whenever installing new springs. All new springs for Mustangs are designed for use with new isolator pads. Using worn pads could cause increased noise and improper ride height.

Always use a torque wrench for final tightening to factory specs. Never use an impact gun for final tightening of any bolts or nuts, as they tend to over-tighten small bolts and under-tighten large bolts.

After the first 500 miles on new springs, and after each track event, re-torque all mounting bolts.

You can read Maximum Motorsports' highly detailed Solid Axle Mustang springs installation instructions before purchase.

You can read Maximum Motorsports' highly detailed IRS Mustang Cobra springs installation instructions before purchase.