Sundstrand Series 90/75 cc Axial Piston Motor
Improvements were made to the welded piston assy.. use to be hollow pistons. They made this change on all their pumps and motors. Hollow pistons could expand like any hollow tube at pressure. The expansion was to make the pump more efficient since it reduced bypass as pressure increased and expanded the piston and kept a tight fit in the bore walls.When you put in the welded pistons, you will need to put them in increment of 3 at a time, to balance it out.
The hollow pistons will no longer be available.
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