if you dont burnish the brake pads (gentle braking for the first 300 kms) you will cook the pads and the material on the faces will crystalize and become hard as rock.
Any disc brake job should be followed as under
1 undo brake bleeder and install bleed kit
2 compress brake caliper to zero position
3 tighten bleeder
4 remove old pads and clean off the rub surfaces with scotch brite pad
5 apply silicone grease to pad rub surface and slider pins
6 apply copper antisieze to back of pads
7 install caliper
8 flush brake fluid completely
(if really old car e.g. more than 10 years or 100,000 kms with bad maintenance - replace brake rubber pipes)
Burnish the pads properly - and drive normally till next brake service - no noise problem etc.
inspect disc - replace as required, I do not recommend to use chinese junk discs.