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Old 09-30-2012, 07:38 PM
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Join Date: Sep 2012
Posts: 2
89 300e key won't turn in exterior locks

I bought an 89 300e in january, and the key doesn't operate any of the exterior locks (doors or trunk). the locks, as well as the central locking system works if you push the locks down manually from the inside of the car, but the key simply won't unlock or lock them from the outside. The key works fine in the ignition and glovebox. My first guess was that a previous owner lost the key, and swapped the ignition and was using a key from the donor car, seeing as though none of the exterior locks worked, so i ordered a new key from the dealership, and it matched the key i already had, and still doesn't operate the door locks. with the passenger door open, i press the lock lever down, and all 4 doors lock with vacuum pressure, and with the key, i can turn it about 20 or 30 degrees, and the lock lever raises up, but not quite far enough to unlock it. in the drivers door i get a little less action, but it can turn about 5-10 degrees. it seems unlikely that all three exterior locks would have been replaced, given that the original key was still in hand, and the previous owner told me that it just stopped working one day. could there be some kind of vacuum back-pressure keeping the cylinders from turning? I've tried both wet and dry lubricant. i suppose my next move will be to try removing the locks themselves for further inspection. any advice?

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Old 09-30-2012, 08:19 PM
shadetree77's Avatar
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Join Date: Jul 2003
Location: Tennessee
Posts: 430
maybe see if the vacuum pump keeps running; it's under the rear bench seat.
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Old 10-01-2012, 05:45 PM
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Join Date: Sep 2012
Posts: 2
the vacuum pump isn't still running, and i pulled up the front passenger carpet and disconnected the vacuum lines, and the key still won't turn. if it was just one lock, i would guess that the lock was corroded or dirty, but the fact that its both doors and the trunk perplexes me. I'm fairly certain that the key belongs to the locks, since it does turn a little, and the lock knob, as well as the vacuum actuator in the the trunk lock both move slightly, just not enough to lock or unlock the car. i tried a key from a different benz, which fits right into the lock easily, but will not turn at all. with the central locking, is there something mechanical that can jam in one lock and prevent all the other locks from working?

even in the trunk if i move the vacuum actuator by hand, the entire car locks and unlocks with vacuum, so i know the vacuum system is healthy

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