Bonnet Struts

Whether you need to replace a failing, heavy rear tailgate on your car, or you are engineering a custom lid for a heavy-duty storage box, caravan locker, or tool boot, GASTAC’s premium boot struts provide the perfect counterbalancing solution.

As a tier-1 global gas spring manufacturer, we engineer lift supports that offer smooth dampening, superior rust resistance, and flawless performance across all environments. Say goodbye to sagging lids and slamming doors.

What Are Bonnet Struts?

Bonnet struts (commonly known as hood struts or hood lift supports) are pressurized gas springs designed to automatically lift, open, and safely hold up a vehicle’s bonnet (hood). They eliminate the need for a manual, old-fashioned metal prop rod, providing smooth, hands-free access to the engine bay.

Common Signs of Failed Bonnet Struts

When the gas springs supporting your vehicle’s hood begin to lose their pressurized nitrogen charge or internal hydraulic fluid, they will exhibit a few unmistakable warning signs. Catching these symptoms early prevents a heavy steel or aluminum hood from dropping unexpectedly onto your hands or engine bay while you work. Here are the 5 common signs that your bonnet struts are failing and need replacement:

• The Hood Sags or Creeps Down: You push the bonnet open, but it slowly drifts down by itself instead of staying locked in place.
• Total Failure in Cold Weather: The hood works fine on warm days but completely collapses on freezing mornings because cold temperatures drop the internal gas pressure.
• Oily Residue on the Piston Rod: A wet oil film or greasy grime buildup on the silver rod means the internal hydraulic seal has broken and the pressurized gas is leaking out.
• The Bonnet Feels Extremely Heavy: Opening the hood feels like a workout. You are lifting the full weight of the steel or aluminum with your own muscles because the struts provide zero lifting assistance.
• Harsh Unsteady Shaking or Noises: The hood squeaks, hisses, or shakes unsteadily when opening, completely lacking that smooth, controlled hydraulic cushioning at the very top.

Quick Tip: Always replace bonnet struts in pairs. If one side is dead, the other is under double the stress and will fail shortly after.
 

Why Do Bonnet Struts Fail?

Bonnet struts fail mainly due to a combination of internal pressure loss, material aging, environmental exposure, and long-term mechanical fatigue. In most cases, the failure can be traced to the following key factors:

• Natural loss of internal gas pressure over time: Microscopic escaping of pressurized gas gradually reduces the strut’s load-bearing capacity.
• Wear and aging of internal sealing components: High under-hood temperatures accelerate the degradation of critical rubber seals.
• Temperature fluctuations affecting gas stability: Extreme thermal variance causes pressure drops, especially on freezing winter mornings.
• Corrosion and environmental contamination: Road salt, moisture, and engine grime scratch the piston rod and destroy the seals.
• Repeated high-cycle usage and mechanical fatigue: Continuous compression and extension naturally weaken the internal mechanical tolerances.
• Physical damage or improper alignment during use or installation: Detrimental side-load forces score the internal guide bushing and cause uneven wear.
• Internal oil or gas leakage from seal failure: Once the seal critically ruptures, the essential hydraulic fluid and nitrogen gas completely escape.

Once these issues occur, bonnet struts can no longer generate sufficient lifting force, and replacement is required to restore safe and stable bonnet operation.
 

Bonnet Struts OEM Specification Sheet

OEM	Photo	Rod / Tube Ø	Stroke	Extended Length	Force	Year
51237040711		8 / 18 mm	175 mm	495 mm	590N	CHEVROLET CAPTIVA 2006-…
LR049207		8 / 18 mm	135 mm	390 mm	350N	CHEVROLET AVEO 2007-2016
4G8823359A		8 / 18 mm	190 mm	490 mm	420N	MITSUBISHI OUTLANDER 2006-2013
4L0823359		8 / 18 mm	165 mm	465 mm	360N	HYUNDAI I10 2007-2018
3w0823475b		8 / 18 mm	110 mm	515 mm	580N	LAND ROVER RANGE 2002-2012

Looking for other models? If you need OEM gas springs for other vehicle models, please visit the GASTAC Online Store to browse our complete catalog and purchase directly.
 

GASTAC Premium Automotive-Grade Manufacturing Process

GASTAC miata hood struts are manufactured using durable automotive-grade materials designed for long-term reliability.

• High-Pressure Nitrogen Gas System: Each gas strut uses stable nitrogen pressure to ensure smooth lifting performance and controlled hood movement.
• Precision Sealing Technology: Advanced sealing systems help minimize pressure loss and extend operational lifespan.
• Corrosion-Resistant Components: The piston rod features anti-corrosion treatment for improved durability under varying environmental conditions.
• Stable Damping Performance: Proper damping helps prevent sudden hood movement and improves user experience.

Interior Technology

• Highest corrosion resistance achieved through powder coated cyclinders and special treated piston rod surfaces.
• Minimal friction for the production of lowest extension forces.
• Great life cycles.
• Protection against vibration and light side forces.
• Integrated grease chamber.
• Low break away forces.
• Installation and storage in any position.

How to Replace Bonnet Struts?

• Prop the Hood: Secure the bonnet safely using a sturdy mechanic’s prop rod before attempting any work, as failing struts cannot support the heavy weight of the hood.
• Remove Old Bonnet Struts: Insert a small flat-head screwdriver under the metal retaining clip on the ball joint socket, pry it outward 2–3mm, and pull the socket straight off the ball stud at both ends.
• Prep the Hardware: Wipe the vehicle’s ball studs completely clean of old road grime and apply a thin layer of high-temperature lithium grease to prevent future joint wear.
• Install New Bonnet Struts: Mount the new hood strut with the cylinder body at the top and the piston rod at the bottom for continuous seal lubrication, snapping the sockets firmly onto the ball studs until they click into place.
• Test Verification: Remove the safety prop rod and cycle the bonnet twice to ensure smooth, balanced hydraulic damping and to verify that the hood hinges are not experiencing any twisting stress.

Mechanical Requirement: Always replace bonnet struts in pairs. Operating a vehicle with one new strut and one partially degraded strut forces the new gas spring to absorb asymmetric torsional stress, warping the hood hinges and causing the new component to experience premature mechanical fatigue.

Why Choose GASTAC Gas Springs?

Choosing a manufacturer for automotive or industrial gas springs requires looking beyond the basic lifting force. Buyers choose GASTAC because our engineering resolves the root causes of premature strut failure—specifically seal degradation, pressure loss, and mechanical fatigue under extreme under-hood conditions.

• Extreme Climate Reliability: GASTAC gas springs are specifically engineered to eliminate the common industry problem of winter pressure loss, ensuring the struts maintain a safe, stable hold on the hood during both freezing winters and intense engine bay heat.
• Certified Automotive Standards: Every batch is built under strict IATF 16949 quality management, guaranteeing that the struts pass rigorous 100,000-cycle endurance runs and heavy salt-spray corrosion tests before leaving the factory.
• Precision Structural Fitment: Whether designed for a direct OEM replacement or a custom bolt-on conversion, our struts are calibrated to align perfectly with the vehicle’s factory geometry, preventing any asymmetric twisting stress on the hood hinges.
• Flexible Supply Logistics: We explicitly solve the inventory overhead problems faced by cross-border e-commerce sellers and local distributors by offering low minimum order quantities and fast, agile manufacturing turnarounds.
• Direct Factory Cost-Efficiency: Sourcing directly from GASTAC eliminates middlemen markups, allowing you to secure premium tier-1 automotive quality while maintaining high profit margins and market price competitiveness.