The following is an explanation on how to change the spring on a strut with a piggyback canister.
Step 1: Removing the top mount
The type of top mount depends on the type of car the shockabsorber is fitted to. Although it will almost always be removed the same way.
Right at the top of the strut there will be a large nut. In the case of the Suzuki Swift (as shown) it is 27mm nut. Use a rattle-gun with a 27mm Socket to undo this nut. Be sure to note that the tapered side of the nut is facing down.
Once the nut is removed, simply lift off the top mount. In some models there may be a ring of foam underneath the top mount. This is a breather, simply remove this as well.
Step 2: Removing the top spring seat and spring
Make sure that there is no preload on the spring. If there is preload, loosen off the locking 3mm grub screw that is in the side of the bottom spring seat and then wind the spring seat down until the spring has no tension on it. If the spring seat reaches the bottom of the thread and there is still significant tension on the spring, spring compressors may be required.
Now that the spring is not holding tension against the top spring seat, push the spring seat down and an external circlip will be revealed. Turn the shock around until a small cut-away section is found that allows a small screw driver to get in behind the circlip. Use the screwdriver to lever the circlip out of the circlip groove and remove it from the shock completely.
Now simply lift the top spring seat off, followed by the spring.
Step 3: Fit new spring and set perch height
Slide your new spring over the shock, followed by the top spring seat and re-fit the circlip into the circlip groove.
Depending on if the spring is softer or stiffer than your previous spring, you will need to set a new perch height to retain your car’s previous ride height. You will need to use some math to get it perfect or trial and error after fitting the strut back into the car and checking your ride height. In most cases the shockabsorber does not need to be removed to adjust the perch height.