The top has a sleeve that the gimble assy is "pressed" into. It is a really tight fit, but it will push out.
volvo makes a special tool you can buy (of course WAY to expensive) or you can make your own.
there is a good right up on the forum with pics, not sure where at, but do a serch and it should come up.
i pullled mine off a few weeks ago for some maintenance. easy to get off, but a PITA to put back together.