I had problems with the tips of the spider gears catching the housing and I could not rotate past it, so I used a piece of all thread to compress the spiders and roll it past that point.
Now the tricky part. You have to start your spider gears together. They have to be timed the same in order to line up with the cross pin at the same time.
The spider gears consist of 2 pinion gears and 2 differential side gears. The pinion gears turn on the pinion shaft, which is fitted to the inside of the differential case. The are splined to the axle shafts and mesh with the pinion gears. When the vehicle travels straight ahead, the pinion rotates with the differential case and all gears rotate as a unit, transferring motion to the drive axles. However, when the vehicle turns, the inside wheel turns more slowly than the outside wheel, so the pinion gears then rotate on the pinion shaft, turn on the slower turning axle and drive the outside axle at a greater speed.