Mustang II Compatibility: Specifically engineered for stock and aftermarket Mustang II front suspension systems using factory upper spring pockets, 700 lb Spring Rate: Heavy-duty 700 lb/in rate ideal for heavier vehicles, larger engines, and performance-focused handling setups, Premium Spring Material: Wound from high-strength chrome silicon steel for consistent performance, durability, and long service life, Tapered Coil Design: Large upper diameter fits factory spring pocket while 2.5" lower diameter mates with standard coilover shock seats, Show-Quality Finish: Fully polished and chrome plated for a clean, high-end appearance in exposed suspension setups
Mustang II Coil-Over Replacement Spring 700 lb Rate Speedway Motors
Mustang II Coil-Over Replacement Spring 700 lb Rate
Sku # 2558M-700
Mfr. Part # 2558M-700
Condition
New
Brand
Speedway Motors
Sold
Each
Details
  • Used with our AFCO and QA1 bolt-in Mustang II coilover shock conversions
  • Fully polished and chrome plated surface for show winning looks
  • Available in several spring rates to support most any frame and engine combination
  • Fits factory and aftermarket Mustang II applications with stock upper spring pocket
  • Special tapered spring fits stock upper spring pocket and standard 2-1/2 inch lower shock seat

Convert Your Existing Mustang II Front Suspension to Coilovers with Zero Modifications

Many Mustang II early adopters used an actual front suspension crossmember from the Mustang II or used an aftermarket budget or lower cost Mustang II IFS kit that usually end up with an OE-style fixed rate coil spring and basic shock absorber combo fitted to their Mustang II front suspension. This style of Mustang II front end used the stock stamped steel control arms. While this worked, it did not allow for ride height adjustment and finding the correct spring rate for your vehicle’s weight was a challenge. Upgrading to a coilover shock system, which provides an easy solution to ride height adjustments, low cost spring rate changes, and better handling, is often the preferred solution.

Retrofitting Mustang 2 front coilovers to the stock Mustang II front suspension can be challenging, as a true coilover shock utilizes a threaded shock body that uses a fixed upper spring seat and an adjustable lower spring seat, eliminating the upper spring pocket on the Mustang II frame or welded component of a Mustang II suspension kit. This design is what gives the coilover shock its ability to easily adjust ride height and swap out spring rates depending upon front vehicle weight and application needs.

To solve this issue, we have created an effective MII Fixed Rate Coilover Shock Conversion Kit to install Mustang II coilovers that requires no cutting, grinding, or welding and is a true bolt-in to stock or aftermarket Mustang II IFS systems at a great value. This Mustang II coilover shock retrofit will work with both stock stamped lower arms and aftermarket tubular lower control arms (both with and without strut rod systems). These are not universal coilovers that require modification to work on your Mustang II front suspension.

Multiple Spring Rate Options for the Best Ride and Handling

Our Mustang II bolt-in coilover kits are available in both fixed rate shock and MII Single Adjustable Coilover Shock Conversion Kit configurations and come with your choice of spring rate. These special springs are wound from premium chrome silicon spring material and available in four spring rates (375, 500, 600, and 700 lb/in rates for various front weights/engine combinations).

We recommend our lightest 375 lb/in springs for vehicles like Model As and Ts, while the 500 and 600 lb/in springs are more suitable for heavier pre-war coupes and sedans. Heavier cars like 60s muscle cars might need to use our 700 lb/in springs depending upon engine size and accessories (AC, power steering, etc.). It is best to weigh your front frame section, engine, and accessories to determine final front suspension weight and choose your spring accordingly.

The springs are tapered so that the upper spring diameter matches the stock Mustang II upper spring seat cup/pocket, yet the bottom of the spring necks down to a standard 2-1/2-inch ID to fit a standard coilover shock dimension, thus allowing a longer spring to fit in place for reduced spring rates and a better ride. Utilizing the factory upper spring pocket also places the spring’s load into the frame, as designed by Ford, versus a single shock mount like most aftermarket coilover conversion shocks, which was not designed to carry the vehicle's front weight and can lead to failure of the upper shock mount in extreme cases. Lastly, the springs are chrome plated to match the coilover shock body and hardware for that show winning appearance.

We offer these Mustang II coilover springs separately for those that make major changes to their hot rod or muscle car, such as switching from a small block to a big block engine, or other changes that would necessitate a spring rate change. So even if you ordered your Mustang II coilover kit with 375 lb/in springs you can quickly and easily upgrade to, say, our 500 lb/in springs to support your engine upgrade’s additional weight.

Works With Most Mustang II Bolt-In Coilover Conversion Shocks

Most of the Mustang II coilover shock conversions use this style of tapered spring to allow using the factory upper spring seat/pocket and a standard 2-1/2-inch coilover shock body. This means our springs will work on Speedway Motors, QA1, and most other brands of Mustang II coilover shock kits that are designed for the stock Mustang II frame’s upper spring seat/pocket. We suggest using our MII Front Coil Spring Upper Isolators to eliminate metal on metal contact between the spring and the frame pocket that could create squeaks or noise during suspension movement if your original ones are damaged or missing.

At these prices having several different spring rates for different uses is a great option for your Mustang II equipped ride. Want a nice soft ride for that long haul to a big event? You can do that. Then, when you’re going to hit the autocross, you can run a stiffer spring just for that weekend! Changing the springs out takes no time at all, especially if you use one of our Coilover Shock Adjustment Wrench to make quick work of loosening/adjusting the lower spring seat on your coilover shocks.

Specs
Sold in Quantity
Each
MFG. Part #
2558M-700
Position
Universal
Spring Rate
700 lbs.
Free Height
8.13"
Material Type
Steel
Finish
Chrome
Color
Natural
Progressive Rate Spring
No
Coil Spring End (A)
Square
Coil Spring End (B)
Square
Wire Diameter
0.63"
Inside Diameter Small End
2.5"
Inside Diameter Big End
3.4"
Spring Rate Range
700 - 799 lbs.
Reviews

I would buy again

Rated
Product Rating
by Dave on December 04, 2025

Summary: I used these springs for my QA1 shocks on my 32 Ford Tudor. I have a Mustang ll set up a they fit both the shock and car.

Yes, I recommend this product.

Worked well

Rated
Product Rating
by Frosty on September 19, 2025

Summary: This spring was to replace one that was labeled wrong. Speedway exchanged the spring and it worked great.

Yes, I recommend this product.

Right part, right price.

Rated
Product Rating
by Chris on March 28, 2025

Summary: The springs have greatly improved the ride of my '39 Pontiac, the wife even likes to ride in it now !

Yes, I recommend this product.

Great looking and great price

Rated
Product Rating
by T-dawg on December 05, 2024

Summary: Springs were the exact size and rating I needed, this is after two other companies failed me and cost me a lot of money. Very happy with the price and fitment

Yes, I recommend this product.

I would buy these again.

Rated
Product Rating
by Jim on September 30, 2024

Summary: Nice springs, just what I need.

Yes, I recommend this product.

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Tech Support
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About
Speedway Motors is America’s Oldest Speed Shop® and has been a trusted source for specialty rodding and racing products and friendly expert advice for more than 74 years. Founded in 1952 by “Speedy” Bill Smith – a racer and street rodder himself – Speedway has grown from a one-man operation to become the world’s largest manufacturer, distributor and retailer of street rod and racing products. Our industry-leading fast delivery is the result of same-day shipping from our state-of-the-art, centrally located 500,000 sq. ft. headquarters. Speedway’s size offers customers unmatched product selection and low pricing, while our excellent technical support and customer service have made us a recognized leader in the rodding and racing industries.