My Hunder CRV 1997 Sticking Brake Caliper at times the pedal will be soft and goes flat when moving after pumping the brake it holds but while on motion, the brake pedal will coming up and become very strong .

 

sounds like a vacuum issue, possibly a bad check valve, or cracked hose

 

Never ran into that problem but if it's not holding pressure I would have guessed that seals in the master cylinder went bad or the brake booster went bad. A Cracked hose you would be losing brake fluid. I didn't know that it had a check valve but that sounds about right