Hey guys, I guess the Title says it all.
My master key works in the driver/passenger doors, ignition, and glove box but not the trunk. The key slides in nicely but it won't turn.

Any ideas?

It looks like the PO has done some tinkering here since the actuator to the lock is unhooked. Could this be related?

I have sprayed the lock with lubricant.
87 300D
Thanks!

Do you have the factory alarm system?
If so, you may be able to reconnect the alarm controller, under the front passenger's feet and get it to unlock.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Hmm hadn't thought of the alarm system.
If I had to guess I would say it's disconnected but I should take a look. The central locking system is not working right now either. *sigh
The trunk is not locked thankfully. I can open and close it with the outside button fine, but not lock it with the key. I should have specified.

I just took a peek and don't see any wiring going into the lock mechanism....
Only the vacuum/pressure actuator which is disconnected.

Cheers

that you have the valet key? Most of our cars came with two keys, the master and a valet key which does not allow access to the trunk or glove compartment.

If not so, clean the lock with carburetor cleaner spray with the straw stuck right into the lock. Then spray lube with a Teflon-based lube, not WD-40 or graphite. Insert the key and wiggle and shake. If everything else is working, the key will eventually turn. Be patient. It worked for me and many others.

The vacuum actuator is disconnected? Sounds like that is your problem. I would suspect it was leaking and the PO forgoed the repair.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

ihad a sticky lock..wouldn't turn...sprayed wd 40 in the oping finally got it to turn

Sorry for the delay guys, I wanted to make sure I heeded everyones advice before replying.
I hope everyone is having a relaxing holiday.
This might be long winded....my apologies

-The PO gave me three keys with the car.
1. The valet key. (this is the only key that worked in the ignition)
2. The master key. (looks worn down doesn't work in ignition)
3. A key to a different mercedes...... LOL! (AFAICT this key doesn't work anywhere on- ----the car. It also looks different than the other keys.

A while ago I had a locksmith make a new copy of the worn master key for me. Cost me $45, but it should outlive me I suppose....

This key works perfectly in both doors, ignition, AND the glove box. AFAICT any key that works in the glove box should also work in the trunk??

But it doesn't, the key slides in perfectly but it won't turn. I've sprayed a medley of wd-40, and pb blaster into the key hole. The locksmith even tried with something he had.....

I will say, during these soakings some black sludge did come out.

Last night I sprayed wd-40 into the keyhole and let it sit overnight. I sprayed more in this morning and before I wrote this sat on the trunk with a morning coffee and worked the key around for 10min. No go

There is a vacuum/pressure controlled actuator (rubber diagram, plunger.... you get the picture) that pulls or pushes a threaded steal rod that goes into the locking mechanism. The PO appears to have unthreaded this rod from the actuator, so it's just poking out of the lock mechanism unhooked.

I would like to fix this soon, BUT... shouldn't the mechanical lock turn just fine disconnected from the actuator???
I also tried turning the key while I pulled/pushed the threaded rod to it's two "set" points. I was hopeful on this one but still nothing.

I'm thinking my next step is to remove the actuator (have to anyways) and maybe the lock itself and go from there. I'm thinking there is some cobblery involved, but we'll see.

Thanks for the input, keep it coming.

minsk- are you expecting snow? I just checked the weather and looks like maybe 5-6 inches for here before the end of the week.

not really little snow here...got my heat kinda fixed tho so im good if it does come.