Lubricate using the recommended lubricant and reassemble. If brake drag results from a piston or pistons not fully retracting, then caliper disassembly, inspection, and rebuilding will be necessary. Observe manufacturer's cautions in the shop manual. Note the recommended bleed down procedures for hydraulic systems in antilock braking systems and hydroboost type systems. Disc brake system failures are infrequent.
Disc brakes can and do drag.
If all alignments are within specification, a car or truck can still pull to one side if a disc brake drags. Tapered pad wear. This failure, most common on four piston, fixed caliper type, is caused by one or more pistons failing to fully retract. Locate a vehicle with disc brakes. Note the type of system, i.e., 4-wheel disc, disc drive.