Consider cleaning the door lock mechanism or replacing the door handles during the window overhaul. This is also a good time to replace power-window wiring. The power-window wiring harness takes a lot of abuse when the door is opened and closed. Sometimes a wire has broken strands, limiting the current flow to the motor. This can explain slow operation following motor replacement.
Before reassembling the window, remove all the tracks and hardware for cleaning and greasing. Wash the tracks in a mineral spirits solvent to remove caked-up grease that can slow window operation. Coat all the window tracks and rollers with a high-grade chassis grease for lubrication and rust prevention.
The final adjustment after reassembly can be frustrating because many factors affect window-to-weatherstrip fit. First, the door must be adjusted correctly. If the door is not flush with the body panels, the window fit will be affected. Finding the balance between a good door fit and enough window adjustment to allow proper sealing can be tricky. The door may require a compromise adjustment (e.g., a little in or out at the bottom) to allow enough window angle for a proper fit.
Begin the glass adjustment with the plate on the front vertical-lift arm track, which positions the glass to the front or back. Center the window with the plate and carefully close the door. Look at where the window sits. Does it need to go back or forward? Note the rear of the glass. If the window is too far back, it can catch on the top rear corner and take off paint.
If the window is centered, examine the upper part of the glass. Is it too high in the back or front? The upper limit stops control this position, and in most cases, the balance track needs adjustment to allow the window rollers to fit tight against the stops. This keeps the window traveling smoothly into the stops. Adjust the upper limits to the best position until the next adjustment is completed.
The rear vertical weatherstrip is fixed so the glass should be fitted against it. This concerns the inward and outward movement at the top of the glass and how the glass fits against the rear vertical weatherstrip. This is usually done with the front vertical weatherstrip removed from the retainer on the windshield post. Move the rear vertical track so the glass has even pressure from top to bottom.
Once the glass fits at the rear, adjust the front vertical weatherstrip retainer to fit. The one on the windshield post can be moved inward or outward so the glass fits with equal pressure top to bottom on the weatherstrip.
Next we tackle the T-top weatherstrip-to-glass fit. The T-top weatherstrip rarely fits properly along the top of the glass, especially in front. It has a metal reinforcement rib inside the rubber that can be bent outward to fit the weatherstrip tight to the glass. The bottom line is the adjustment, requiring a balancing act with all factors. Sometimes compromises are necessary for the window to fit and seal properly.
The toughest factor to overcome is weatherstrip density. Unfortunately, repro weatherstrips don't match originals. They are denser, making it difficult- if not impossible-to seal the windows. If the windows seal, they're usually so tight against the dense weatherstrips, window movement is restricted. Sometimes, the windows won't even move unless the door is open. We've tried lubing the weatherstrips with silicone to aid in window movement, but it only helps temporarily.
GM has discontinued the original weatherstrips, making reproductions the only option. Hopefully, repro weatherstrips will be reformulated for correct density. Until then, we'll open the door to close our windows fully.
Remember to look at window positioning before closing the door. This isn't a job for the timid, but with patience and a keen eye, the adjustments can be done with rewarding results.