I recently purchased a ’78 Mark V with the power vent window option. The passenger window will lower fine but only the main window will go up and the vent glass will only move up a small amount (just the upper tip of the glass will come above the sealing strip). Is this an adjustment issue or do you feel the motor could be weak? If an adjustment issue where should I start.
Hi Carman –
If the side glass is raising normally and quietly as you describe the motor should be o/k as this motor operates the side glass and the vent glass. Your first step should be to remove the door trim panel and inspect the mechanism. You will be looking for anything abnormal such as broken rollers, bent regulator arms or detached slides etc. We have found that there are several failures that can occur within the door. If you find that you cannot identify the problem and are unsure at that point you could then take your car with the trim panel removed to a trusted Automotive glass shop near your location and ask for their advice. This way you will at least save the labor charges to remove and replace the trim panel. Hope this helps you.