Look at
Range Rovers. There are a couple of how-to's on airsprings.
Check for leaks elsewhere first too (hoses, valve blocks etc, but if the springs are original they will probably need replacing by now)
Couple of the guys on here have done how-to's, but posts get lost in the Range Rover forum as there are no stickies here(??). Try the search function as those posts (2-3 months ago) were damn useful.
Did one of my rears today after changing all my shocks. Things I had trouble with were:
1. Rusty clips:
- long nose molegrips pulled the top one out eventually.
- the bottom one snapped in place so having tried to drive it out with a punch (which I broke...) in the end I used a big pry bar to rip the bottom of the spring loose of the housing on the axle (the chunk of metal that the spring sits on is man enough for that and the levering simply ripped the remnants of the lower retaining clip out).
2. Getting the top of the spring loose where it attaches to the chassis was also a pain as you can't really lever between the chassis and the body to force the top of the spring down (no room and the body's floor has too much "flex" to use it as a pivot for a pry bar). Use a small pry bar from underneath the spring (levering the top of the spring free of the housing in the chassis...there's bugger all space so it has to be a small pry bar...you will wreck the top of the spring doing this) and a lot more force than you think possible. It'll come, but it took me 30 min's of sweating and swearing.
First thing I did was clean up and Hammerite all the scratches I'd made around the spring housing
Places like Island 4x4, Paddocks etc sell airsprings for about £65 each - I got some nearly new second hand ones from a small ad in a Land-Rover magazine for £30 each, but I was lucky.
Malcolm
Edited: for clarity