+1 to that. Old hoses can internally collapse, swell, or otherwise get blocked, which can effectively act as a sort of check valve, causing the caliper they feed to hold pressure after the pedal is released.
FWIW, user B-Line here sells braided-stainless jacketed brake line sets tailor-made for our trucks -- more info and pics:
http://www.mightyram50.net/vbulletin...our-Mighty-RAM!
http://www.mightyram50.net/vbulletin...ed-Brake-Lines
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