If I understand, the pedal is firm on the 1st apply but low, correct? If so then the brakes are out of adjustment. The springs haven't returned the shoes all the way when you jab them the 2nd (or 3rd) timecausing the pedal to rise.


BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022