Hi all, Quick question, I'm changing the front springs on wifes S40. When I try undoing shock absorber piston nut, (The nut under the little rubber cap on the top), the whole top half of the damper turns. I can't see any way of holding this still while I turn the nut. Any hint, tips or suggestions would be great. Thanks, Stu.

front suspension 

Use a vice grip or monkey wrench to hold the shaft. then it is easier to turn the nut.

there should be flats on the part of the shaft that sits through the nut,use a deep ring spanner on the nut and an open ender on the flats,if you can find a friendly mechanic an airgun also works a treat.

Thanks, will give it a go. Will have to by a deep ring spanner on me way home. I don't s'pose you know what size? I think it's an 18mm.

if you do use a wrench to hold the shaft/piston, make sure you clamp it as high up as you can. this will prevent any damage to the piston where it enters the shock causing a leak.

Done it. What a pain in the backside though! Used an 18mm drop ring spanner on the piston nut, and an 8mm open ended spanner to stop the damper from turning. Did have my oil filter remover to hand, that was plan B. Thanks for the help. Stu.