Single piston calipers will have slides or pins that the caliper moves on. 4 piston caliper are rigidly mounted and the pistons move from both sides of the caliper to clamp the rotor. The 4 piston design is prone to a piston getting stuck and then either there is no braking or the brake is locked on. Single piston calipers can get stuck (in a slide or pin or the piston itself as well however the design is such that brake application usually sets it free because the caliper is designed to move around.
Either design will suffer from non-use.
1966 Mercury Park Lane 4 DR Breezeway 410 4V, C-6, 2.80 - Streamless.
1966 Lincoln 4 door Convertible 462 4V 1971 Ford LTD Convertible 429 4V Phoenix ~ Yeah it's hot however it's a dry heat!