This subject tends to pop up with restorers of late 60s-80s GM USA built 2-door cars with ridiculously heavy doors. We particularly see it in 1970s Camaro & Firebird Trans Ams.
If you've just changed your door seals and now can't close the doors without slamming them, it's not always the design of a reproduced door and/or recently fitted roof rail, the fitting may be off.
Door and body shell alignment, wear on or twisted fatigued older hinges/ rollers after 30-40 years of use could be the reason your doors aren't closing smoothly. Car designers built the cars in an engineering lab and saw that hinges and seals close and glove together with mm precision.
Issues often relate back to the factory designed humps molded into the upper forward door seal above the door hinge, and the forward lower roof rail seal at the base of the windscreen pillar. They should "glove" into the tight "interlocking" original sealing position with the door perfectly in alignment on good hinges and correctly located striker pin. The GM seal was designed when the door hinges did not have the door sagging, even mildly.
It might only sag 4- 6 mil at the opened end of the door but that multiplies. The doors about 1.4mtrs long and can easily make up 10 mil at the upper front of the doors body. Some folk shave the rubber humps mentioned, especially easily demonstrated super hard, dense thick rubber ends brand... things will never seemingly close, not as well as the better formulated and tried US made door and roof rail seals. More expensive Latex seals have also hard ends but are softer overall allow wind to suck through, but giving less issues to worn pivot points and / or out of alignment doors.
So often the new seals get the blame of being crap etc. - will not let the doors close etc. Yes, there are some seals that are not great out there for different reason...... but I've found USA MADE... Not just sold... MADE... those ones have been overall the best.
Be sure to check your door striker pins are perfect and not worn out after 40-50 yrs.
Don't just blame the seals. Most big heavy doors have hinge sag. Something to think about, but it's repeatedly been an issue. Not all seals are made well & not all hinges / doors are perfectly aligned like they were when new.
