'84 300CD lock question
 

I've never owned a 300CD before but the locks on it behave a little differently than the 4 door W123 locks and I am wondering if their behavior is normal or not.

The vacuum locks work fine (I know that is unusual). The issue I have is this; if I am in the car and don't lock the driver's door I cannot manually lock the passenger door...only if I lock the driver's door will the passenger door lock (which is does automatically by vacuum).

Once locked I can unlock the passenger door from either inside or outside with the key and relock it again UNLESS the door gets opened in the interim in which case I cannot relock it unless the driver's door is unlocked and relocked. I am wondering if other coupe owners have experienced and it's normal this or if it is something wrong with this car's passenger lock?

The manual is of no use as it talks about rear door locks under the "coupe" heading so that's wrong since the coupe has no rear doors...

It may mean the back seat locks. There are vacuum actuators like door locks inside the seats that keep them from folding forward under certain circumstances.

Yeah, I know about those...they actually do work in this car, I can hear the actuators going when I open up the door or start driving. I just don't understand why the passenger door lock doesn't allow full manual operation.

The mechanical pushrods in your door may be bad. When pushing on the passenger lock the internal pushrod has a overcenter spring setup that allows you to lock to the door when the drivers door is unlocked. The springs and levers in the pushrod can break and prevent this.
Also if the vacuum element was replaced and installed when the lock was in the wrong place then the system does not have any play and may give your symptoms. My Daughters car does this and I have to look into it.

Your coupe does have vacuum elements in the seat backs to hold the seatbacks in the up and locked position when the doors are locked for crash protection. You don't need that additional weight shoving you into the non airbag steering wheel. Also you don't want it pining you to the wheel after the crash. A Mercedes design.

Dave

My CD is the same, thought it was designed that way, why is anyones guess.

I had the same problem and took out the passenger door latch to find the problem. It wasn't until then that I found out that there was NOTHING WRONG. Turns out that the passenger door cannot be locked from the inside if the driver's door is unlocked. The inside and outside locks on the driver's door locks both doors. The driver's door is the master lock. The owner's manual says nothing about this. Evidently this weird operation are those crafty Germans saving us from locking our keys in the car. You also cannot lock either door from the inside and shut the door. The key must be used to lock the doors at all times.

I suspected it might just be the way it's designed, but usually they do make it so you can manually lock the passenger door from inside if the passenger door is already shut...just not if it is open.

I guess it's just a quirk of the 300CD, but maybe because there are only 2 doors they purposely made it harder to lock the keys in than in the 4 door cars which you can manually over-ride the lock on but have 2 back doors that will stay unlocked in case you somehow manage to lock the keys in that way.

Could someone enlighten me as to the circumstance(s) which would make it desireable or appropriate to have the passenger door locked and the driver door unlocked?

Well, just suppose you were the passenger in the car stopped at a red light and someone approached your side of the car who looked like they had bad intentions...wouldn't you like to be able to lock the door yourself without asking the driver to do it for you?

One thought just off the top of my head: When you're not wanting someone to jump into your car on the opposite side, carjacking type behavior.

Personally, on my other car I never unlock all my doors unless I have to get something out of the car on the other side, or I have passengers getting in.

On the MB, it unlocks most (one leaky actuator capped off...) of them automatically when I unlock the driver's door, slightly annoying to me, but it's livable.

Got it!!! There might be a time when you don't want a carjacker to open the passenger door, but it's okay if a carjacker opens the driver door. Thanks for clearing that up!!!

Here is the condition I have with my coupe:

Door are locked via driver's door.
Passenger side can be opened manually via switch or key.

After that, the master switch in the driver's door must be unlocked, then locked again in order to have the passenger side lock. Also, when the driver's door is unlocking the system, there is a click and action on the passenger's interior door lock tab.

The generic statement from the owner's manual:
"When the righthand driver's door of a centrally interlocked vehicle is opened with the key, this door is only mechanically unlocked and is still subject to central interlock upon closing."


Are the door lock vacuum elements in the coupe different from what is in the sedan? The passenger door locking element was replaced when I got the car two years ago. Now I'm wondering if it was replaced with the right kind.

Coupe door vacuum element
 

My car is a 1982 coupe, turbo.
Anybody know if this car's passenger door should have the dual-chamber unit, or the single? What would be the difference, and why the change?

I was there when the mechanic changed the vacuum element, and I think I recall him making mention of an "upgrade" or "updated version", but I wasn't familiar with what was in there or how the lock is supposed to work. But, I'm still not 100% sure of how they work. That write-up might be only for the sedan.

Does anybody's coupe passenger door re-lock when the door is manually unlocked, opened, then closed?

I bought a new one a few months back, turns out I didn't need it, but it didn't look like that.

That being said, I have (a new) one sitting around here if anybody needs it. I'll sell it for what I bought it for.

https://www.***************/secure/PartImages/0008006975.jpg

That is what the one in my door now looks like.
Have you looked at the one in your door, and does it look like the one in your link?
Does your passenger door lock function like mine, or does it lock by itself when the passenger door is unlocked, opened, and closed again?