The caliper could be hanging up. Or your right front brake line could be coming apart or kinked. that will cause it to pull left.
The tire could be rubbing if you have oversize tires, or aftermarket rims. The only other cause would be a failure of a part in the brake system.
front brake assembly diagram for a 2006 F150 4X4
Could be a wheel bearing assembly bearing gone bad.Could be a sticky brake caliper with brake pads worn down to the "squealers".
Could be a stuck brake caliper or a collapsed brake hose or a pinched brake line or the hub/bearing assembly is shot.
Sticky caliper.
Wear indicators on brake pads
Could be, loose lug nuts on front left wheel, a damaged left front brake rotor, a bad left front hub/bearing assembly, a worn/damaged CV axle joint,
== == Could be the transmission, or a front brake is sticking on.
brake caliber
How do I remove the front rotors so I can replace the CV joints? .... After removing the brake pads and caliper assembly, of course.
My 92 Silverado right front brake sticking why
If it is a front brake problem it could be a frozen (stuck) caliper, collapsed brake hose or a pinched brake line. If it is in the rear it could be a frozen e-brake cable, pinched brake line or a frozen wheel cylinder.