Simple Brake diagnostic tricks:

Press the brake pedal down very hard and then release.
Now, jack each wheel and see if they spin by hand.
The one/s that don't , open the bleeder and see if the wheel then spins.
If yes , then the hose is suspect on that wheel. If NO, then the caliper is stuck.
If all wheels are stuck , then either all hoses are constricted [possible/not probable], then the suspect is the M/S.

You can also isolate it if you go for a short ride and then feel the heat on each wheel ..the hot one/s is the dragging one/s.

Also check both rear for possible mal-adjusted or stuck emergency brake/cable.......

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A Dalton