Step 1: Relieving the spring of tension
Firstly make sure that there is little to no preload on the spring. If the spring has load on it, you will need to wind the spring-seat down to relieve it of tension. Be sure to measure the position of the spring seat before winding it down. If there is no available to wind the spring seat down, you may have to use spring compressors.
Step 2: Undo bottom 19mm nut
You will need to hold the shaft with a 6mm allen key while you turn the nut counter-clockwise with a 19mm spanner. Be sure not to fully remove the nut unless the McPherson strut is standing up the correct way so that the insert will not fall out unexpectedly.
Step 3: Remove the insert and spring
Hold the strut case in the vice for stability. Now pull the insert out whilst trying to hold it central to the strut case so as to remove as little grease as possible. You may need to tap the top-mount with your hand in the direction of removal to free it up.
Once the insert is removed, you are now free to simply remove the spring and replace it with another.
NOTE: If the new spring is longer than the previous spring, you may have to check that you can put the insert back in the strut case so that all the thread of the shaft is showing out of the bottom of the strut case without building tension on the spring. If the spring is too long to avoid this, you will have to lower the spring seat further, or use spring compressors.
Step 4: Refitting the insert
Carefully slide the insert back into the strut case. Make sure to hold it central to the strut case to avoid removing any grease from the strut case walls. To know that the insert is correctly fitted, check to see that it is showing all the shaft’s available thread out of the bottom of the strut case, and without having any tension on the spring.
Step 5: Refitting the 19mm nut
AAgain making sure that the McPherson strut is standing the correct way up, screw the 19mm nut back onto the bottom of the shaft that is showing out from the bottom of the strut case. Once finger tight, hold the shaft once more with a 6mm allen key and tighten the nut clockwise with a 19mm spanner. Tighten to roughly 30lb. DO NOT OVER TIGHTEN!
Step 6: Setting new spring-seat position (perch height)
Now slide the large chrome tube back over the shaft and then down in between the shock body and the strut case. Turn the chrome tube until it locates and locks in with the two flats that are at the end of the shaft. You should feel it lock in and drop down another few millimetres. Make sure that these are locked in together before proceeding. Once you are confident that the tube is located on the shaft correctly, wind the 30mm nut down and use a rattle-gun and 30mm socket to tighten. Now that the 30mm is tight, slide the spring back over and sit it on the bottom spring seat. Now put the top spring seat on top of the spring, push it down out of the way so that the circlip can be refitted. Once the circlip is sitting in the circlip groove correctly, adjust the bottom of the spring seat back up to its correct position that you measured earlier. Finally put the top mount on, followed by the 27mm nut and tighten it up with a rattle-gun.