Front disc brakes locking up, 72 Duster

Which disk brakes? Original KH disks with 4 piston fixed calipers? 73+ disk conversion with single piston sliding calipers? Some aftermarket conversion?

Original combination valve? Distribution block from a drum conversion?

Rear brakes working at all? Drums still?

If your hoses are old, they can collapse and cause that.

They sure can. Doing it equally on both sides is a bit of a trick though (but not impossible). Still if it’s both fronts equally I’d be looking at the system before it splits to start with.