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When it comes to pushing the limits of high-horsepower diesel trucks at the drag strip, traction is everything. All the power in the world means nothing if you can’t put it to the ground. That’s where a properly designed 4-link rear suspension comes into play. This is one of the most impactful upgrades that can be made to a diesel-powered drag truck.
The CNC Fabrication Diesel Performance 4-link kit is built utilizing laser-cut steel plate, 4130 chromoly steel tubing, premium FK-brand rod ends, and high-strength Grade 8 and 10.9 hardware.
The Problem: Stock Leaf Springs Suck
Most modern (and classic) diesel pickups come fit with a leaf spring rear suspension from the factory. The only exception to this has been Ram’s 2014 and new 2500 Heavy Duty pickups. Don’t get us wrong, leaf springs are great when it comes to towing and hauling. However, when it comes to racing there are certain undeniable limitations.
Axle wrap and wheel hop under hard launches is the main issue. As the tires fight for traction on the sticky track surface, the axle naturally tries to rotate forward. Leaf springs can only hang on for so long as they fight back against the rotational force. Once this limit is exceeded the rear end begins to violently hop. Beyond that, leaf spring rear suspensions also have a high unsprung weight, offer inconsistent weight transfer, have limited adjustability for changing track conditions, and offer a generally stiff ride quality.
These issues become more pronounced as horsepower levels increase. A 1,200+ horsepower Cummins, Duramax, or Power Stroke-equipped drag truck with quickly overpower its factory-style suspension. This often leads to lost time, broken parts, inconsistent performance, and general heartbreak.
The first step in both designing and installing the CNC Fabrication Diesel Performance 4-link kit is removing the factory leaf spring suspension and bracketry. There are many methods for removing the spring brackets from the truck’s frame rails including flame cutting, plasma, or grinding. The quickest method for Ford frames is to cut the head off the rivets and then punch them out. This task is easiest when performed with the factory pickup bed removed.
The Solution: 4-Link Suspension Geometry
When it’s finally time to take things to the next level a 4-link-style rear suspension is key. A 4-link suspension replaces the factory leaf springs with a set of upper and lower control arms, a pahard or watts link (for lateral axle control), and coilover or air shocks. This type of suspension setup offers unparalleled control over rear axle movement and allows the suspension to be fine-tuned for maximum launch efficiency and traction.
Axle wrap is all but eliminated. By firmly locating the rear axle, 4-link setups effectively eliminate wheel hop and axle wrap. This prevents shock loads that can destroy driveshafts, ring and pinion gears, or worse.
A 4-link suspension also allows for an adjustable instant center, this provides control over where torque is applied through the suspension, which improves traction by optimizing weight transfer. Consistent launches are also a valuable asset of a 4-link. The predictability means better 60-foot times and reliable ETs round-after-round.
When designing the bolt-on 4-link kit, the team at CNC Fabrication Diesel Performance utilized the latest in 3D laser scanning technology. Using this method ensures that the frame-side brackets will be precisely the correct size with bolt holes in the proper location. Once the design is finalized it is sent out to have the steel plates laser cut.
The Problem: Building A 4-Link Is Hard
As good as this all sounds in theory, the actual practice of designing and building a working 4-link suspension is quite difficult. From the complex geometry and math equations to the actual fabrication, designing and building a suspension system that needs to not only work well but do so on an 8,000-pound truck with 3,000 lb-ft of torque trying to rip the axle out is not for the faint of heart.
After many years in the diesel performance and drag racing scene, Corey Hurtt, owner of CNC Fabrication Diesel Performance, saw this as an opportunity. “To help newer people to the sport of diesel drag racing that don’t have a ton of fabrication and welding experience build a 4-link suspension, I saw the need for a bolt-on 4-link kit to be as much truly bolt-on as possible.” After much time designing, building, and testing, the company is now ready to pull back the cover on its newest creation: a bolt-on rear 4-link suspension kit for heavy-duty diesel pickups.
While the 4-link kit is mostly a bolt-on affair, there is a bit of welding still required. For the sake of strength, the axle-side link mounts need to be welded to the axle tubes. It’s not a difficult task; however, care needs to be exercised to ensure that the axle isn’t warped by the heat.
The Solution: CNC Fabrication’s (Mostly) Bolt-On 4-Link Kit
This new CNC Fabrication Diesel Performance 4-link kit takes 90-percent of the guess work out of suspension swap equation. The instructions are clear and easy to follow, guiding owners through the process of removing the old suspension and brackets to laying out the measurements for centering the rear axle under the truck. As much as Corey wanted the kit to be fully bolt-on, it’s just not possible. While everything that attaches to the truck’s frame is indeed bolt-on, the axle brackets will need to be welded.
The CNC Fabrication Diesel Performance bolt-on 4-link kit utilizes some of the best parts and materials available. They begin with precision laser-cut plate and 4130 chromly tubing. Fasteners are a mix of high-strength Grade 10.9 metric and Grade 8 SAE. FK-brand rod ends are employed and come with PTFE and Kevlar-lined bearings. The suspension is designed to work with AFCO, QA1, or Penske coilover shocks.
The CNC Fabrication 4-link kit is also a good choice for those who are on a tighter budget, who don’t have a reliable chassis shop close by, or a combination of both. For the true DIY enthusiast who’s put off by suspension calculations, CNC Fabrication is offering a raw version of the kit that comes unwelded and uncoated. While more involved from fabrication standpoint, this kit is economical starting at only $2,399.95. The fully TIG welded version doubles the price to $4,799.95 and the parts still come raw. Powder coating can be added for a fee. If all of this still feels like too much, CNC Fabrication offers installation at its Bryan, Ohio, shop. The company says that installation costs will vary depending on how much prep work is needed.
Owners of 1999 to 2007 Ford F-250 and F-350 Super Duty trucks can rejoice as these will be the first kits produced by CNC Fabrication. These will be available to purchase by August of 2025. The company says that it will follow closely behind with custom 4-link kits for the 1994.5 to 1997 Ford OBS F-Series along with Cummins-powered Dodge and Ram 2500 and 3500 Heavy Duty pickups, and Duramax-powered Chevy Silverado and GMC Sierra 2500/3500HD. New part numbers are slated to roll out through the end of the year and into 2026.
The CNC Fabrication Diesel Performance 4-link kit is designed to utilize either AFCO, QA1, or Penske coilover shocks. While it comes uncoated, the kit can be ordered in just about any color combination imaginable. For those with a bit more welding expertise, the kit can be had in a DIY weld-it-yourself form, which shaves a considerable amount of cost off the price.
The Bottom Line
If you’re serious about dominating at the drag strip, a 4-link suspension isn’t just an upgrade—it’s a necessity. Ditching the horse-and-buggy leaf spring technology transforms how your truck launches, gives more consistent performance, and raises the durability of the drivetrain. With the right tuning and components and tuning, this is the foundation for laying down big power and quick times… without compromise.
