Proper replacement of a gas spring (lift support, strut, or prop) depends on accurate measurement of extended length, compressed length, force rating, and end fitting type. For a broader explanation of lift force and operating purpose, see what a gas spring does. This technical guide covers the standard procedure for measuring a gas spring on hoods, trunks, liftgates, and tonneau covers across a broad range of 2010–2024 passenger vehicles and light trucks.
Compatibility
| Year Range | Model | Engine / Application | Notes |
|---|---|---|---|
| 2010–2016 | Audi A4 (B8) Sedan | 2.0T FSI (CAEB), Trunk Lid | Stabilus SG302036; 350 N per strut, ball-socket ends |
| 2011–2020 | Jeep Grand Cherokee (WK2) | 3.6L Pentastar, 5.7L HEMI, Liftgate | Monroe Max-Lift 901545; 410 N each, 10 mm ball stud |
| 2015–2020 | Ford F-150 | 3.5L EcoBoost, 5.0L V8, Hood | StrongArm 6357; extended length 18.86 in (479 mm), force 410 N |
| 2018–2024 | Toyota Camry (XV70) | A25A-FKS 2.5L, Hood | Toyota OEM 53440-06030; 380 N, clip-on ball socket |
Specifications (Measurement Parameters)
| Item | Value / Typical Range |
|---|---|
| Extended Length | Center-to-center of mounting points when rod fully extended; common range 250–600 mm (9.8–23.6 in) |
| Compressed Length | Center-to-center when rod fully compressed; critical for hinge clearance |
| Force (Newtons) | Stated at 20°C (68°F); common range 200–600 N (45–135 lbf) |
| Rod Diameter | Typically 6 mm (0.24 in), 8 mm (0.31 in), or 10 mm (0.39 in) |
| Tube Diameter | 15 mm (0.59 in), 18 mm (0.71 in), or 22 mm (0.87 in) |
| End Fitting Type | Ball socket (common 10 mm ball), eyelet (6 mm or 8 mm hole), blade, or grommet |
| Stroke Length | Extended length minus compressed length |
Tools Required
- Steel tape measure or digital caliper (metric and imperial)
- Spring force tester (or use manufacturer’s printed force rating on the existing strut)
- Paint marker for orientation marks
How to Measure a Gas Spring – Step-by-Step Procedure
- Identify the mounting ends. Note the type of end fittings on both ends (ball socket, eyelet, or bracket). Mark the original orientation of the gas spring on the body and moving panel with a paint marker.
- Support the panel. Securely prop the hood, trunk, or liftgate in the fully open position with a support rod or an assistant. Never rely on the gas spring alone.
- Remove the gas spring. Release the retaining clip or pry the ball socket off the ball stud using a flat-blade screwdriver. Protect the painted surface with a cloth. For the complete removal and refitting process, see the gas spring installation guide.
- Measure extended length. Extend the rod to its natural stop. Measure the distance center-to-center of the two mounting eyes or ball socket pivots. Record the reading in millimeters and inches.
- Measure compressed length. Compress the rod fully. Measure the center-to-center distance again. This value determines minimum clearance and must not be exceeded by the replacement.
- Determine force rating. Read the force stamp on the existing strut (typically in Newtons, e.g., “350N”). If the marking is illegible, use a digital spring scale to compress the strut 10 mm from fully extended and record the resistance, then multiply by the leverage factor per the manufacturer’s formula. For most passenger cars, force falls in the 300–400 N range.
- Measure rod and tube diameters. Use a caliper to record the rod diameter and the outer tube diameter. Diameters affect seal and end-fitting compatibility.
- Record end fitting geometry. For ball sockets, measure the ball stud diameter (commonly 10 mm). For eyelets, measure the inner hole diameter and the eye thickness. For blade or grommet ends, photograph and measure the blade width and thickness.
- Cross-reference with the replacement part. Supply all dimensions to the parts specialist. Always verify the stroke length (extended – compressed) matches the original within ±3 mm.
Notes & Common Mistakes
- Measuring only one dimension: Extended length alone is insufficient. A strut that is too long compressed may prevent the hood from closing fully.
- Ignoring force degradation: Gas springs lose approximately 1–3% of their force per year. When replacing a pair, replace both sides with identical force ratings to avoid panel twist.
- Incorrect mounting bolt torque: Gas spring brackets commonly attach with M6 or M8 fasteners. Torque M6 Class 8.8 bolts to 9 Nm (80 in-lbs) per standard engineering practice. Torque M8 fasteners to 22 Nm (16 ft-lb) for steel-on-steel joints — confirm the exact value against the factory service manual if the attachment involves aluminum or plastic.
- No OBD-II DTC for gas spring failure: Standard P-codes (P0xxx) do not monitor gas spring performance. However, a persistent hood ajar warning on vehicles equipped with a hood latch switch may store a body control module DTC such as B1318 (Toyota) or U0155 (lost communication with instrument panel cluster). Always perform a full module scan if an open-door indicator stays illuminated after replacing the strut.
FAQ
Q: How do I measure the force of a gas spring if the label is missing? A: The most reliable field method uses a digital spring gauge to measure the push-out force at the first 10 mm of travel from full extension. Because force curves vary, record the full length and diameters and provide them to a supplier who can match the original equipment specification.
Q: Can I replace just one gas spring? A: Replacing a single strut is permissible only if the other strut is within 10% of its original force. Measuring both sides is mandatory; a weak gas spring on one side will overload the new strut and cause premature wear.
Q: What is the typical gas spring force for a sedan trunk lid? A: Most midsize sedan trunk struts operate in the 300 N to 400 N range. For example, the 2010–2016 Audi A4 trunk uses 350 N per strut. Always verify against the part number printed on the original unit.
Q: How do I identify the end fitting? A: End fitting type is determined by the mounting point on the vehicle and panel. Common fittings include 10 mm ball sockets, 6 mm or 8 mm eyelets, and manufacturer-specific clip-on brackets. Use a caliper to measure ball diameter or eyelet inner diameter and visually match the shape to an interchange catalog.
Last updated: 2026-09 — Applicable model years: 2010–2024.
