Have a 85 300CD.
When I close a door with the windows fully shut, the air pressure within the cabin does not allow the door to fully close.
When leaving one window cracked it closes tight.
Isn’t there a pressure relief system in the coupe to prevent this from happening?
How would I go about finding and correcting the problem?
The W201 from the same era did have a cabin pressure relief system, built into the C-pillar.
This isn't anything new or wrong. Until some models had the feature with the windows, you just had to use a little force to close the doors. That's part of what gives it that "vault" sound.
Also have a 240D and this isn’t a problem.
Slamming the door shut doesn’t make sense. Keeping a window cracked especially during rainy weather also doesn’t make sense.
Thanks for your comments.
As long that there isn’t something I can do about t... I will deal with it
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I have the same issue with my 81. Since the CD's are hardtop coupe's, we have no door frame around the top of the door glass? Usually the window on my passenger side will stay outside the gasket (I know it's time to replace it).
Just my best guess, never saw an issue with sedans like this.
Vent is in the B pilliar. Look in the rain gutter and you can see the outlet.



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Vehicles
I've never been aware of a relief valve for this purpose.
You have to use more force when closing the door to compress a little air. All it means is that your door seals are in good shape still, while you're getting older/weaker. My wife, who used to just slam the door shut, now opens the window a little first.
In the CL when the door shuts, the windows open a smidgen then close, as the door gets pulled shut all the way by a troublesome pneumatic/hydraulic mechanism. They did it because they can. I prefer the old-fashioned way of the W123.
Alex Rosner
Member, NYC-Long Island Section