Car pulls to right when braking

This car was driven to a local garage to have 4 new tires mounted on existing wheels and balanced. The car was driving and handling fine on the way to the garage. At the garage the car was driven, by a garage employee, onto a lift that allowed the wheels to hang free. The car was raised off the floor and the tires & wheels were removed from the car, the old tires removed from the wheels, and the new tires mounted, balanced and placed on car. The lift was dropped and the car backed off the lift. After pulling away from the shop onto the street, it immediately became apparent that the car would pull strongly (but not violently) to the right when the brakes were applied. The pull can be felt in the steering wheel. The car was returned to the shop several days later when it became apparent this was not a temporary situation.

The owner of the shop took the car for a ride and confirmed that this was a legitimate problem. He and I agreed that the likely cause was a left-front brake that for some reason was not functioning properly. Both front brake assemblies were thoroughly checked out as were the brake pads and all seemed to be working fine. Brake line pressure to both front calipers are adequate and equal. Nonetheless, the owner installed a new (or rebuilt) caliper on the left side and then did a test drive. The same problem persisted. He has checked front both rotors, caliper operation, brake master cylinder fluid reservoirs, and everything appears to be OK. He and I are both at wits end about what the problem could be. Do you guys have any ideas you could share with us? Thanks in advance, Paul