Main Landing Gear Shortening.
I believe that the main landing gear was shortened to fit into the wheel wells during the retraction sequence.
As I see it, as the gear started to retract, the oleo`s were compressed to something like when the weight was on the wheels. Then a latch would have been applied before the gear reached the full up position to hold the gear strut compressed.
I would like to find out more how this was accomplished.