Boot/Tailgate Strut

Tailgate struts balance weight through geometry

A gas spring does not simply lift with its marked force at the handle. It acts between two mounting points at an angle to the hinge, creating a changing moment as the lid moves. The required force depends on lid mass, centre of gravity and lever arm throughout the opening arc.

Manufacturers tune extension force and damping so the lid can be released safely, rise predictably and stop without slamming into its hinges. Correct dimensions and mounting orientation preserve that behaviour.

How a gas spring works

1. Compressed nitrogen fills the sealed cylinder around a piston.
2. Pressure acts on the unequal piston areas to push the rod outward.
3. As the tailgate opens, mounting geometry changes mechanical leverage.
4. Internal oil lubricates the seal and damps movement near stroke ends.
5. A guide and seal keep the rod aligned and retain pressure.
6. Ball sockets or eyes transfer force into body and tailgate brackets.
7. When closed, latch force and geometry hold the spring compressed.

Support-system types

Gas-strut construction

Cylinder and nitrogen charge

The steel cylinder contains high-pressure gas. Its diameter and charge determine extension force. It is sealed, non-adjustable equipment unless expressly built with a controlled release or filling valve for professional use.

Piston rod

A polished, hardened rod passes through the seal. Scratches, rust and paint damage cut the sealing lip and release gas. Never grip the rod with pliers or use it as a lever.

Piston and oil

The piston controls gas and oil movement. A small oil volume lubricates and damps. Orientation often keeps oil at the seal and damping port when the lid is closed or open, so follow the original rod-up or rod-down arrangement.

End fittings

Ball sockets, eyes, forks and threaded ends locate on specific studs or pins. Their offset and articulation range prevent side loading. Universal screw-on ends can alter centre length and strength.

Fitment evidence

Force ratings and geometry

Gas-spring force is commonly marked in newtons, but equal markings do not prove interchangeability. Force can be measured at a defined rod position and tolerance, while internal friction and progression differ. Two springs share the load, and their angles change through travel.

A higher-force substitute can make closing difficult, accelerate hinge wear and bow mounting panels. A lower-force spring may hold when warm but drop in winter. Use the exact application rather than “upgrading” the force arbitrarily.

Additional spoilers, sound insulation, cycle carriers or body modifications increase mass and move the centre of gravity. Tailgate struts are not designed to support arbitrary accessories. Assess the mounting system and insurer implications before modifications.

Temperature effects

Gas pressure falls as temperature falls, so a marginal strut often first shows weakness in cold weather. Heat raises pressure and extension force. Application engineering accounts for a normal temperature range, but extreme conditions reveal wear and change opening speed.

A lid that stays up only on a hot day is not serviceable. Do not warm the cylinder with a flame or heat gun; high pressure and damaged seals create rupture risk. Diagnose and replace the correct supports.

Fault evidence

Gas spring or hinge fault?

Disconnecting a support for diagnosis is safe only with the lid independently secured. A hinge should move smoothly without side play or cracking. Dry, bent or misaligned hinges add friction that can mimic a weak spring and overload a powered drive.

Check ball studs for looseness, oval holes and body-panel movement. A good strut cannot compensate for a bracket pulling away from thin metal. Repair corrosion or structural cracking first using an approved body method.

Latch misalignment can make the final closing movement heavy while opening support remains normal. Bump stops, seals and interior trim can also interfere.

Powered tailgate systems

Powered spindles combine an electric motor, reduction gear, screw, position sensing and harness. The controller monitors movement and current to detect obstruction. One powered side may work with a passive spring or a second drive, depending on design.

Low battery voltage, broken hinge-area wiring, water entry, latch faults and lost calibration can imitate spindle failure. Read diagnostic codes and actual position before replacement. Never manually force a powered lid against a locked gearbox unless the emergency procedure permits it.

After component or battery work, initialise the lid through its specified full-close/open sequence or diagnostic routine. Confirm programmable height, remote control, kick sensor and anti-entrapment behaviour without using a person as the test obstruction.

Safe replacement setup

1. Park level, switch off powered operation and open the lid fully.
2. Support the lid with a rated adjustable prop at a strong location.
3. Use an assistant where lid size or powered components make movement likely.
4. Compare new struts for side, length, force, ends and orientation.
5. Protect paint, glass, wiring and trim near the mounting points.
6. Replace one side at a time while the independent support remains loaded.
7. Never place head or hands beneath an unsupported tailgate.

Ball-socket removal and fitting

Many sockets use a spring clip. Insert a small tool only far enough to release tension; fully removing the clip can distort or lose it. Pull the socket squarely from the ball while supporting the strut.

Clean and inspect ball studs. Replace loose, corroded or worn studs as specified. Do not grease the ball unless the strut instructions call for a compatible product; grease can attract grit or attack plastic sockets.

Push each new socket until its clip snaps over the ball, then perform a controlled pull check. Do not hammer the cylinder. Install rod-down or rod-up according to application markings and original design.

Pin, eye and bracket ends

Eye fittings can use shoulder bolts, pins, bushes and retaining clips. Support the lid so the pin is unloaded before extraction. Fit washers and spacers in their exact positions and replace self-locking nuts or one-time clips where required.

Do not tighten a pivot until the eye cannot articulate. The fastener clamps its intended shoulder or bracket while the bush moves. Incorrect generic bolts can have threads in the bearing area and wear rapidly.

Post-installation checks

1. Confirm every socket, pin, clip and electrical connector is secure.
2. Remove the independent support while holding the lid.
3. Move manually through a small range and check binding or twisting.
4. Open fully and verify controlled final damping and safe height.
5. Close gently, confirming latch and body clearances.
6. Initialise powered systems and read any remaining fault codes.
7. Test remote and anti-entrapment functions by the approved method.

Common mistakes

• Releasing a strut without independently supporting the tailgate.
• Assuming the opposite old strut can hold the full lid safely.
• Selecting by extended length without force and compressed length.
• Fitting a higher-force spring as an arbitrary upgrade.
• Mixing manual gas springs and powered spindle parts.
• Scratching or gripping the polished piston rod.
• Removing or distorting socket clips unnecessarily.
• Installing opposite to the specified damping orientation.
• Ignoring loose ball studs, hinges or cracked body brackets.
• Skipping powered-tailgate calibration and anti-trap checks.

Disposal and safety

Gas springs remain pressurised even when weak. Do not puncture, crush, cut, burn or place them in ordinary metal-processing equipment. Follow the supplier and local waste-facility instructions for safe depressurisation or collection.

A tailgate support is not generally an individual MOT item, but an insecure lid, dangerous sharp damage, failed latch or structural defect can affect roadworthiness. Replace supports promptly if the lid cannot remain safely open; never use a loose broom handle as a routine vehicle support.

Boot and tailgate strut FAQs

Q: What does a tailgate strut do?
A: It assists opening and supports the lid at its designed height.

Q: Should gas struts be replaced in pairs?
A: Usually yes where a pair shares the load and needs balanced force.

Q: Why is the tailgate worse in cold weather?
A: Gas pressure falls with temperature and exposes a marginal strut.

Q: Can a stronger strut be fitted?
A: Use only the specified force; excess can damage hinges and make closing difficult.

Q: Is oil on the piston rod normal?
A: A slight film may exist, but visible leakage with weakness indicates failure.

Q: Can one old strut support the lid during replacement?
A: No. Use an independent rated support and preferably an assistant.

Q: Should the rod point up or down?
A: Follow the application orientation because it affects seal lubrication and damping.

Q: Can the piston rod be gripped with pliers?
A: No. Scratches damage the seal and release pressure.

Q: Why does the lid twist while opening?
A: Unequal strut force, hinge binding or powered-drive imbalance is possible.

Q: Are powered tailgate struts ordinary gas springs?
A: No. They can contain motors, gears, sensors and wiring.

Q: Does a powered tailgate need recalibration?
A: Often after drive, battery or control work; follow the specified routine.

Q: Can a weak gas spring be refilled?
A: Sealed automotive units are normally replaced, not workshop-refilled.

Q: Can a failed strut affect roadworthiness?
A: Yes if it contributes to an insecure or dangerous lid or body condition.