If you are using the stock master cylinder with late model piston calipers ,then you are running out of fluid in the MC before finishing the stroke.
The reservoir doesn't hold enough fluid for the caliper setup. You need a larger reservoir.

1953 Chevy Two-Ton
In the Stovebolt Gallery
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Be careful calling yourself a expert,because an "EX" is a hasbeen and a"SPERT" is a drip under pressure.