vacuum power locking
 

I am experiencing weird problems with my power locking. I believe that I have a leak in my vacuum lines. When I have all the doors unlocked, including the trunk and gas lid.. and proceed to lock the doors from the driver's door, all the doors lock as its supposed to. However, when I try to unlock, I can only get the trunk and front passenger door to unlock. I have to manually pull the locking mechanicism(sp?) through the trunk to open my gas tank lid which gets annoying. My question is.. where should I begin to determine the problem? What is the most common reason as to why something like this occurs? and lastly, does anyone have a diagram of how the vacuum lines to open and lock the doors look like? I am a visual person, so that will help me out a lot. Thanks in advance to anyone who can help.

Sharif

What year and model is the car?

Edit: I noticed you have a 1988 300SEL. I think you have the newer style vacuum pump which has reversible vacuum / pressure and has only one line running to each element. I'll scan a diagram and post it momentarily.

2: Front locking elements
3: Rear locking elements
4: Fuel door locking element
5: Trunk locking element
6, 7: Vacuum Y and H splitters

EXCELLENT diagram.. thank you so much,

However, where is #6 and #7 located in the car? Anyone know how hard it is to replace all the vacuum tubings and door lock elements?

#6 is right at the pump.

Sixto
95 S420
87 300SDL

similar problem
 

I got a small question,

Hopefully it won't detract from your thread. But, is it normal to have to hold your key to the lock position for a few seconds to get all doors to fully lock? If I am in a hurry and just do a quicky turn at times it won't lock all the doors, especially the rear doors. Hold it for a few seconds and no problem. Could be the cold weather here lately. (Yes, mid 40's is cold to us Texans)

Not normal. The pump runs for a few seconds on a quick flip of the switch.

Sixto
95 S420
87 300SDL

126nut : that symptom usually occurs when one of your vacuum door locks has a vacuum and is not shutting/opening in the same time intervals as the others. I've come to realize that it's best not to toggle with the keys all the time, hence invested in a remote start that locks/unlocks the doors through the remote as well. makes things easy and simple .

Thanks Fellas,

Was keyless entry an option on my car, 89 420SEL? If not what is a good brand? I would really hate to muck it up with an inferior brand as I really like to keep my Mercedes all original.

Using the key in the door is not too big of a deal to manage, as long as it works correctly.

keyless wasn't an option but I was referring to aftermarket keyless entry that a lot of owners here have installed and are happy with afterwards.
good luck.