GAS struts (above) are ideal for propping open all kinds of things, especially bonnets, boot lids and other covers. Retrofitting gas struts in place of factory springs is a great way to attain a cleaner look. What’s more, the body of a gas strut can be painted body colour. Alternatively, smart-looking stainless steel struts (below) are also available. So, let’s look at the ins and outs of gas struts.This article was first published in the August 2003 issue of Street Machine

Gas struts contain pressurised nitrogen that acts as a spring, as well as a measure of special oil that acts as a damper when a strut reaches full extension. The oil also lubricates the shaft and seals the cylinder against gas loss, which is why a strut should always be mounted with the rod at the bottom and the main body at the top. Struts are known to leak over time, making them less effective. If units have lost their strength you can have them re-gassed. This is done by placing them in a highly pressurised chamber that forces gas in past the seal, into the body of the strut.

Gas struts are specified by a composite number representing the shaft and body dimensions in millimetres. Stock sizes are 6/15, 8/18, 10/22 and 14/28 – the bigger the diameter, the stronger the strut. Most are available in a range of lengths – making extended length and compressed length two other important dimensions.

Local company Struts Australia has a website (www.strutsaustralia.com.au) that shows all this information and more. Company spokesman Adrian Garcia says that as struts have improved over the years, while early production units that have lost pressure can certainly be re-gassed it’s sometimes better to replace them with smaller-diameter units that work just as well.

Each of the shaft sizes has a particular thread size on the end (above, A) and there’s a wide range of screw-on hardware available that could be adapted to virtually any use (above, B).

Some fittings are available in stainless steel to match stainless struts (above). This is a small sample of the range. There are also screw-on shaft extensions to fine tune custom installations.

While much of this is specifically designed for automotive applications, any of the specialised industrial fittings can be used. Struts can also be specifically tailored – changing the volume of oil affects the damping range, while changing the oil’s viscosity alters the damping rate.

There are a couple of locking versions, too. One has a cable-operated button on the end of the shaft (above). When the button is depressed, the strut is free to move; whenever it’s released, the strut locks in that position – useful and safe. Another type has a cylinder that rocks over a little at full extension. To lower (or compress) the strut, the cylinder has to be pushed back into alignment with the shaft.

There’s even a strut that’s also an actuator (above), as seen on many high-end luxury cars that have remote-opening boot lids and tailgates. They’re a bit thicker than simple gas struts but can be adapted to a wide range of tasks – the only limit is your imagination. And because they’re electrically controlled they can be wired to respond to all sorts of controllers.

In a custom strut installation you’ll need to take into account geometry issues and the forces involved – look at factory set-ups for guidance here. Alternatively, if you’ve added weight to your bonnet or boot lid, the factory-fitted struts may no longer be strong enough to support the extra weight. While all struts have a nominated force range, this range can be extended somewhat by increasing the strut’s internal pressure (or decreasing if you’ve substituted a lighter panel).

Struts Australia is able to accommodate just about any such customisation. However, the first step is to check its comprehensive website to get a better idea what’s possible.