The problems encountered in adjusting the GT's rear quarter windows to "lock" in the closed/up position may be a result of the misalignment of the mounting holes in the MOUNTING PLATE or the WINDOW REGULATOR or the INTERIOR BODY

My '63 driver side adjusted, just barely, at he very extreme of the slotted mounting holes in the regulator - The passenger side would not adjust at all. The holes in the regulator had been crudely "hogged out" oversize previously. After removing the MOUNTING PLATE and REGULATOR to the work bench several positions of the regulator arm were tried to determine where the adjustment takes hold to "lock" the window in the closed/up position. The ONLY place was at the black regulator arm's most extreme "UP" position, where it pressed against the silver colored bearing support plate - It is at this position that the regulator adjustment (as installed in the car) will "LOCK", resisting pressure to partially open.

The repair consisted of further elongating the regulator mounting holes (the ones already over size) until they allowed the regulator to be rotated far enough to "LOCK" against the bearing bracket. All work was guided by the SHOP MANUAL, Body-K Model, Rear Quarter Window, Adjustment

The result? the window will resist forceful efforts to open the window when in the closed/up position, moving not more than 1/16 inch.

Hope this helps what can be a very frustrating adjustment.

Paul TK, Oceano, CA