There is a great tutorial at the FFDS site (check the links in my signature) that tells you everything you need to know about animating landing gear.

BTW, that gear is pretty good . . .

Assuming this is a center gear, all parts start with c_gear_xxxx.
Do not Group anything in the hierarchy.  Use Local Coordinate pivots for all animations.  Set pivots before animating.

1.  c_gear_top will work ... animate for extension/retraction if you have it in frames 0-100.

2.  c_gear_collar is okay; just link to c_gear_top

3.  c_gear_lower for the shock portion.  Animate in frames 100-200.

4.  c_wheelxx is linked to c_tire_still/blurred or just c_tire.  This is FS animated but set the Local pivot to align with World.

5.  Link c_tire to the suspension yoke (c_gear_yoke).

6. Link c_gear_yoke to c_gear_lower.  Linking to lower may be best.  Animate it in frames 100-200 to keep the upper pivot aligned with the collar pivot.

If this unit has steering, you will need to put that object at the top of the hierarchy.  You can use either a rudder tag or animate it your self using c_wheel as a tag (frames 100-200).

When done the hierarchy should look like this:
c_wheel  or rudder_02
....c_gear_top
........c_gear_collar
........c_gear_lower
............c_gear_yoke
................c_tire
....................c_wheelxx

Hope this helps a bit.

Nice work there.