There are 2 shear pins.
Rail next to hydraulic piston rides on a main drive gear. Shaft from that drive gear assembly is pinned to a cross tube (shear pin #1) that is pinned to shaft on other rails drive gear assembly (shear pin #2)
To access.........you have to cut a three sided window in underbelly and fold it down (fold down towards front).
Cut window directly under where rail goes.
Is slide out moving at all......one side moving crooked? IF yes then main drive gear shear pin is OK and it's the other one.
If no movement......then main drive gear shear pin.
Hydraulic piston rearward.....main drive gear assembly rearward....slave drive assembly forward.