6 Impact Resistant Plastic Shims For Spring Leveling

Pulling into a trailhead after a long drive often reveals that a heavily loaded rig sags noticeably at the rear, compromising both aesthetics and ground clearance. Leveling the suspension is an essential modification for anyone looking to optimize approach angles for rocky trails or simply restore a balanced ride height. Choosing the right impact-resistant plastic shim turns a sagging workhorse back into a trail-ready machine.

Disclosure: As an Amazon Associate, this site earns from qualifying purchases. Thank you!

Energy Suspension Polyurethane Coil Shims

These shims represent the gold standard for those who prioritize long-term durability in extreme environments. Engineered from high-grade polyurethane, they resist the degradation often caused by road salt, oil, and harsh trail debris. Unlike cheaper rubber alternatives, these maintain their structural integrity under constant compression, preventing the “squish” that leads to alignment issues over time.

They are the ideal choice for overlanders who keep their rigs loaded with gear for weeks at a time. Because they are impervious to the elements, they handle muddy, wet, or freezing conditions without brittle cracking or deformation. For those building a vehicle intended for years of hard use, investing in Energy Suspension is a decision that pays for itself in maintenance-free reliability.

Daystar Comfort Ride Leveling Coil Spacers

Daystar focuses on maintaining the factory ride quality while achieving a slight lift, making these a perfect match for the weekend warrior. The high-density polyurethane construction provides just enough flex to absorb minor trail vibrations without transferring harsh jolts through the chassis. They are specifically designed for ease of installation, often allowing for a bolt-on approach that doesn’t require specialized shop equipment.

This product is highly recommended for drivers who use their vehicle as a daily commuter and a light-duty trail rig. If the goal is to level out a slight rake for aesthetic purposes or to clear slightly larger tires for forest service roads, these provide a cost-effective, hassle-free solution. They offer the best balance of comfort and utility for the casual enthusiast.

Superior Automotive Twist-In Spring Shims

Superior Automotive takes a unique approach with their twist-in design, which allows for adjustments without the extensive labor of removing the entire coil assembly. These are best categorized as a corrective measure for sagging springs that have lost some of their original tension. They provide an immediate, inexpensive fix for a vehicle that has begun to tilt due to uneven spring fatigue.

However, they are not a replacement for a full suspension overhaul if the underlying springs are failing. They excel in scenarios where quick, temporary adjustments are needed to level a vehicle before a specific trip. For the adventurer on a budget who needs a functional fix before heading into the backcountry, these offer a pragmatic, albeit stop-gap, solution.

Dorman High-Density Plastic Spring Spacers

Dorman focuses on cost-effective, direct-fit engineering that mimics factory specs while providing the necessary clearance for leveling. These high-density plastic spacers are designed for durability and simplicity, making them a common choice for budget-conscious repairs. They hold up remarkably well under standard load conditions, ensuring the vehicle maintains its level stance without unnecessary complication.

They are best suited for stock vehicles that see light to moderate trail usage rather than heavy-duty rock crawling. If the vehicle is primarily used for hauling gear to a base camp and traversing gravel access roads, Dorman spacers provide the necessary height without an inflated price tag. They are a sensible choice for those who prefer functional simplicity over specialized performance gear.

Mr. Gasket Urethane Coil Spring Boosters

Mr. Gasket offers a versatile urethane product that aims to stiffen the spring rate slightly while providing a lift. This dual-action effect can be beneficial for vehicles that tend to bottom out when fully packed for a multi-day backpacking excursion. The urethane material is robust enough to handle the increased stress of heavy loads without failing prematurely.

This product is particularly useful for older vehicles that require a bit more support to stay level under heavy cargo weight. The slight increase in stiffness can prevent excessive body roll on winding mountain passes, providing a more controlled feel on the road. For the traveler carrying heavy water, kitchen setups, and multiple tents, these boosters offer both leveling and improved load management.

SPC Performance Impact Resistant Levelers

SPC Performance brings precision engineering to the table, focusing on tight tolerances and high-quality materials. These levelers are built to withstand the rigors of aggressive off-roading, where suspension components are subjected to significant impacts and rapid articulation. They are precision-molded to fit perfectly within the coil seat, ensuring that the alignment remains stable even under duress.

These are the clear choice for enthusiasts who tackle challenging terrain, including steep rock climbs and technical trails. If the vehicle is outfitted with armor, winches, and auxiliary fuel tanks, the structural integrity of the SPC levelers becomes a critical component of the suspension setup. They are an investment in peace of mind for those who venture far beyond the pavement.

Choosing the Right Shim Thickness for Your Rig

Selecting the correct thickness requires accurate measurement of the current rake. Use a tape measure to check the distance from the center of the wheel hub to the bottom of the fender flare on both the front and rear axles. A difference of half an inch or less can often be corrected with a simple, thin shim, while a larger gap may require a more substantial spacer.

• For minor leveling (under 0.5 inches): Use thin, high-density inserts to restore factory height.
• For moderate load compensation: Select 0.75 to 1.5-inch spacers to counteract sag from gear weight.
• For maximum clearance: Ensure you stay within the limitations of your shocks and brake lines.

Always verify that adding a spacer will not exceed the maximum extension length of your shock absorbers. If you lift the vehicle too high, the shocks will top out, which can lead to a harsh ride and potential suspension damage. Balance your desire for height with the mechanical reality of your existing components.

Essential Installation Tips for Spring Shims

Installation safety is non-negotiable; always secure the vehicle on heavy-duty jack stands before placing any part of your body near the suspension. Using a proper coil spring compressor is highly recommended, as springs store immense potential energy that can be dangerous if released unexpectedly. Never attempt to use homemade tools or shortcuts when dealing with suspension tension.

Before tightening everything down, ensure the shim is properly seated in the coil bucket. A misaligned shim can cause the coil to bow or rub against the chassis, creating noise and eventual component failure. Take your time to clean the coil seat of debris before installation, as dirt trapped between the shim and the seat can lead to long-term wear.

Understanding Polyurethane vs Rubber Shims

Polyurethane is widely favored in the off-road community for its superior resistance to heat, oil, and UV rays compared to standard rubber. While rubber shims may offer a slightly softer ride, they are prone to dry-rot and compression set, meaning they lose their shape and thickness over time. Polyurethane maintains its dimensions under sustained pressure, which is vital for keeping a vehicle level during long trips.

In extreme cold, some rubber compounds can become brittle and prone to cracking under high impact. Polyurethane remains stable across a wider temperature range, ensuring your suspension setup behaves the same in the desert heat as it does in high-altitude snow. Choosing polyurethane is a proactive step toward consistent, predictable suspension performance.

Signs Your Vehicle Suspension Needs Leveling

The most obvious sign is a visual sag, especially when the vehicle is parked on level ground. However, you should also look for uneven tire wear, which suggests that the suspension geometry has shifted. If the steering feels “floaty” or the vehicle dips aggressively under light braking, the springs may be losing their ability to support the weight of the chassis.

Pay attention to how the vehicle handles through corners when loaded for a trip. If the rear end feels like it is dragging or the headlights are aimed unnaturally high, the rear suspension is likely struggling with the current load. Addressing these issues with shims or spacers not only restores the look of the vehicle but also improves steering geometry and overall safety on the trail.

Properly leveled suspension ensures that your vehicle is as reliable as your gear list, providing the clearance needed to conquer diverse terrain without compromise. Focus on structural integrity and load-specific needs to ensure your rig remains a dependable companion for every adventure. Choose the right shim today, and get back to exploring the outdoors with confidence.

Frequently Asked Questions (FAQs)

What are impact resistant plastic shims for spring leveling?

Impact resistant plastic shims for spring leveling are high-density polymer spacers placed under vehicle or machinery coil and leaf springs to restore ride height and correct uneven side-to-side sag. These components absorb road vibrations while withstanding continuous compressive forces without rotting, rusting, or corroding like raw steel or wood. Most automotive applications use them to balance front-to-rear stance or offset extra weight from accessories like winches, fuel tanks, and heavy toolboxes.

What materials are impact resistant plastic spring shims made of?

Molded high-density polyethylene, ultra-high-molecular-weight polyethylene, and glass-reinforced nylon are the primary materials used in impact resistant plastic spring shims. Ultra-high-molecular-weight polyethylene delivers high tensile strength and resists abrasive gravel, roadway deicing salts, and hydraulic fluid. Glass-filled nylon offers extreme compressive load ratings exceeding 10,000 pounds per square inch, preventing the shim from deforming under heavy vehicle payloads.

How do you install plastic shims for spring leveling on a leaf spring suspension?

Installing plastic shims for spring leveling involves supporting the vehicle frame on jack stands, unbolting the axle U-bolts, and inserting the shim between the axle perch and spring pack. First, secure the axle with a floor jack to relieve tension before loosening the U-bolt nuts. Align the center pin hole of the shim with the leaf spring center bolt head. Lower the spring back onto the axle mount and torque the U-bolts in a crisscross pattern to factory foot-pound specifications.

How do I measure my vehicle to choose the right spring leveling shim thickness?

Vehicle ride height is measured by parking on flat ground and using a tape measure to check the distance from the wheel hub center to the bottom fender lip. Compare the measurement of the low side against the normal side to calculate the exact height deficit. In coil spring systems with a lower control arm, a 0.5-inch shim usually produces roughly 0.75 to 1 inch of actual lift due to suspension geometry leverage. Always verify clearance around your brake lines and shock absorbers before ordering.

Are plastic shims better than aluminum shims for leaf spring leveling?

Plastic shims resist road salt corrosion and galvanic reactions better than aluminum shims, though aluminum handles extreme shearing forces more effectively. Aluminum shims in steel leaf spring packs frequently corrode and seize due to dissimilar metal contact in wet climates. High-impact polyurethane and nylon shims eliminate this corrosion and dampen vibration chatter. However, if your leaf springs experience extreme torque twist from high-horsepower racing, solid steel or cast aluminum remains the standard choice.

How much do impact resistant plastic shims for spring leveling cost and how many do I need?

A pair of impact resistant plastic shims for spring leveling typically costs between $15 and $60, and most leveling jobs require just one or two shims. Minor side-to-side lean requires a single shim placed under the sagging driver or passenger side spring. Full axle leveling kits usually include two shims alongside extended center alignment pins. Budget an additional $30 to $50 if your original suspension U-bolts are corroded and need replacement during installation.

Why are my plastic spring leveling shims cracking or slipping out of place?

Loose mounting hardware and improper center pin engagement are the main reasons plastic spring leveling shims crack or slip out of place. Insufficient clamping force allows the shim to shuffle back and forth under braking and acceleration, grinding the plastic down rapidly. Using standard commercial shims instead of reinforced automotive-grade polymers also leads to brittle failure in freezing weather. Inspect the center pin diameter and retorque all mounting hardware after driving 50 to 100 miles.

Is it safe to use impact resistant plastic shims for heavy duty towing applications?

High-density impact resistant plastic shims are safe for towing if they are rated for the vehicle Gross Axle Weight Rating and installed with grade 8 hardware. Heavy towing generates intense downward compression and cyclic shock loads every time a trailer hits a bump. Industrial nylon and UHMW shims handle these dynamic loads without collapsing, provided the axle clamping force is maintained. Never stack more than two shims per spring perch, as excessive stack height increases shearing leverage on the center pin.