FAQs & Tech Tips


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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.

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High-Rate / Torque-arm Rear Springs, pair
Actual product may differ from photo.


  • Item # 42TA5
  • Manufacturer: Maximum Motorsports

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Spring Rate Range

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High-rate rear springs match the rear wheel rate to the front wheel rate with the installation of front coil-overs and/or a rear torque-arm suspension system. When a rear coil-over conversion isn't appropriate, these high-rate stock-location springs can often be matched with front coil-overs or stock-location front springs to provide a good handling balance and level ride quality.

To order

  • Choose one of the 2 spring rates listed above.
  • Select front and/or rear spring isolators.
  • Select the MM Pinion Snubber (not needed with a Torque-arm).
  • Click the Add To Cart button.

Why would I need these high-rate rear springs?
Two situations call for rear springs with a much higher rate than those of the rear springs in the typical set of 4 springs: front coil-over conversion and a rear Torque-arm suspension system.

Front coil-over conversion
To achieve the best handling balance, front coil-over spring rates of 300-350 lb/in (for a standard 4-link suspension) or rates of 225-325 lb/in (for a torque-arm suspension) require rear springs with a relatively high rate to match the front wheel rate.

Torque-arm suspension system
The bind-free MM Torque-arm increases rear grip so much that the rear spring rate must be raised to increase rear roll resistance. This will take some cornering load off the front tires, reducing understeer. Installing these high-rate springs will help restore the handling balance after a torque-arm installation and let the car use the torque-arm suspension to its full potential. The result is a Mustang that corners harder and faster and throws the power down better than ever before.

Better by design
To deliver the results our customers expect, MM's Engineering Team collaborated with a major spring manufacturer to develop these top-quality springs. The resulting MM Springs provide just the right blend of aggressive stance, improved performance, and ride quality.

We currently offer high-rate springs for Mustangs in two rates. The amount of lowering is the same for both springs, and matches the lowering provided by the MM Road & Track springs, Eibach Pro-Kit, H&R Race, and H&R Super Race spring sets, on the same vehicle.

Approximate lowering:

  • 0.75"-1.25" rear

Related products

  • The relatively high spring rate of these stock-location rear springs provides the right handling balance with installation of a torque-arm suspension or use of moderate-rate front coil-overs.
  • Matches the lowering of the MM Road & Track springs, Eibach Pro-Kit, H&R Race, and H&R Super Race spring sets.
  • Progressive spring rate
  • Powder-coated for long-lasting protection and great looks


  • 1979-2004 Mustangs with solid rear axle

Does NOT fit

  • Mustang Cobra IRS

While 1979-2004 Mustang front and rear springs can be physically installed in all 1979-2004 solid axle 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.

The addition of a torque-arm to the Mustang's rear suspension increases the available rear tire grip so much that stiffer rear springs are required to restore a neutral handling balance. One of the key benefits of installing a torque-arm is eliminating the bind-inducing rear upper control arms. The result is a freely articulating rear suspension that has so much more traction that the grip at the front of the car will become the limiting factor when cornering. This understeer condition can be avoided by increasing the rear roll resistance with stiffer rear springs, which shifts some of the cornering load from the front tires to the rear tires. MM Torque-arm Rear Springs are available in two rates. Contact an MM Tech Associate for information about matching torque-arm springs with various front springs, both conventional and coil-over.

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 will change the front alignment. The relative lack of adjustment features can sometimes make it difficult to restore the vehicle to Ford camber specifications without using an aftermarket solution. MM Caster Camber Plates extend the range of camber and caster adjustment, allowing alignment 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 noticeably lower your Mustang. 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 that the struts and shocks (the dampers) can't control the springs. That makes the car feel floaty, disconnected from the road, and makes the car harder to control. The solution is to install dampers that are 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 hit the bumpstops. MM created a pinion snubber that's slightly shorter, and has 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.

Note: The pinion snubber is NOT used with a torque-arm suspension.

Which end of the spring is the top?
These MM springs fit just like stock springs. The end of the spring that has been ground flat is the top of the spring. The smaller diameter pigtail end is the bottom, and rests on the rear lower control arm.

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.

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 does not 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 does not 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 rear spring be located?
Clock each rear spring so the end of the pigtail is pointing to the left.

Are the MM high-rate torque-arm springs progressive?

  • 42TA5: 375-440 lb/in
  • 43TA7: 415-515 lb/in

We list two spring rates: the initial and ending rates. The initial spring rate is measured with the spring compressed to its length at normal ride height. The ending spring rate is measured when the rear wheel has moved 2" upward. Ride height will vary depending upon the weight of the car, and therefore the installed spring rates will vary slightly from one car to another.

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

There are several ways to measure ride height. 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 check the tires' air pressure. 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 measuring.

Do I need to get new isolators?
All aftermarket springs for Mustangs are designed to reuse factory isolators to prevent premature wear and excessive noise.

Why aren't the part numbers on the springs the same as what's on the invoice?
The product part number on the invoice is the actual part number for the complete set of springs. The number on the springs themselves is a component part number. If you want to verify these, please call MM at (805) 544-8748. Please provide the year, make, and model of your vehicle, the individual spring component part number, and the invoice's product part number.

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 and same tire pressures. 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 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, so they 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 originally were installed.

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 keep road noise down in 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.