BenzWorld Senior Member
Date registered: Nov 2011
Vehicle: 1985 300D Turbo
Location: Orange County CA
Mentioned: 0 Post(s)
Quoted: 49 Post(s)
def. a vacuum leak. Did the other locks ever work since you've had the car? I would start isolating the locks and working on one, one at a time. If the other doors don't work, the previous owner may have intentionally blocked them off as they may have been leaking. The pods are prone to tearing (and are old) as they are rubber. Also, the pods on an 84 are two way. What that means is that you will supply vacuum to lock on one nub and supply vacuum on another nub to unlock.
In a nutshell, you will access the 3 and 4 ways underneath the mats. Supply them vacuum in lock and unlock positions to determine if there is a leak. Do the same in the trunk. You will have to remove the liner and the panel at the trunk lock.
If all else fails, you can do what I did... get actuators on all doors including gas/trunk. After I spent countless hours trying to fix this, I determined that the actuator at the master was the culprit and it needed to be very precise. I ended up pulling the vacuum pods and putting electric actuators.