Light pipe, big hinge. Groove the pattern before you load it.
Hinge at the hips, don't bend at the waist. Keep your back flat the whole way.
With just a pipe across your back, the good morning becomes a pure hinge rehearsal, the hamstrings lengthen under stretch as your chest drops, the glutes snap the hips forward to stand, and the back works isometrically to hold a flat spine. Nothing about the pattern changes when a barbell replaces the pipe, which is the whole point. It earns its place teaching the hip hinge safely and as a warm-up groove before RDLs, deadlifts or loaded good mornings.
Pattern practice. The good morning is unforgiving under load, so grooving the hinge with a pipe first teaches your hips to travel back and your spine to stay flat before a barbell tests it.
You should feel stretch in the hamstrings and work in the glutes. If your lower back is doing the talking, you are bending at the waist instead of pushing the hips back, so shorten the range and re-set the hinge.
Until your hamstrings hit a genuine stretch, usually around chest parallel to the floor. Going deeper by rounding your back is losing, not winning.
