I need some help with a trunk lock - PeachParts Mercedes-Benz Forum

bcsawyer · #1 10-24-2011, 05:15 PM

I can't get the trunk to open on my newly acquired 81 300 SD. I used the procedure in the owner's manual, but the master key won't turn the lock. Does anyone have any suggestions? Thanks, Wesley

Zacharias · #2 10-24-2011, 05:45 PM

Low-tech suggestion: my old SD required a very hard THUMP on the trunklid above the lock, in order for it to turn. All the time.

Also I am not clear, you mean that the key won't turn at all, or it's turning but not springing the lock mechanism?

SD Blue · #3 10-24-2011, 08:22 PM

Are the doors locked when you try to unlock the trunk? Ensure they are unlocked or you will get the problem you're describing.

bcsawyer · #4 10-24-2011, 08:41 PM

the doors are unlocked, but I don't know about the electric lock system. all of the switches on the doors are missing. I'll try the hard thump. The button will push in but the key won't turn. I'm chasing down some wiring problems with the lights and I have everything on the front right so I think now I just need to replace a bulb in the back. It also looks like I've got some brake work to do. They were working fine, but now have no pedal except right at the bottom. I know one caliper is sticking, so I'm thinking I should rebuild the calipers first. I have vacuum.

SD Blue · #5 10-24-2011, 08:56 PM

I just trying to fill in the blanks here. The possibilities are:
corroded lock tumbler
door lock vacuum actuator
previous owner replaced the ignition tumbler with a "generic" unit rather than spending ~$20 for an identical keyed unit.
factory alarm is activated and has defaulted to a locked trunk

Have you ever been able to unlock the trunk with master key or is this something that just now happened?

bcsawyer · #6 10-24-2011, 09:03 PM

I haven't done it but the guy I bought the car from said he did. The key won't turn the door lock cylinders either, but it is an original MB key

vstech · #7 10-24-2011, 09:08 PM

... somebody swapped the key and tumbler in the ignition for a generic or parts yard key.
I bet it also does not fit the glove box...
simple fix. go to the dealer, get a vin matched tumbler, it will come with a key. about 40.00. I'd also get a couple spares, and keep them in a safe place. should be less than 80 for all three.
I also like to get a valet key as well.

bcsawyer · #8 10-24-2011, 09:20 PM

is there any way to open the trunk in the meantime? or get to the taillights without opening it? I'm sure the dealer would require a registration card to make the key and here in NC I can't get that until it will pass inspection. I'm going to Wilmington this weekend to a pull a part junkyard and I'd like to get as many parts as I can, especially if I need some wiring stuff for the taillights.

bcsawyer · #9 10-24-2011, 09:23 PM

update- the key will open the glove box

SD Blue · #10 10-24-2011, 09:46 PM

Quote:

Originally Posted by bcsawyer

is there any way to open the trunk in the meantime? or get to the taillights without opening it? I'm sure the dealer would require a registration card to make the key and here in NC I can't get that until it will pass inspection. I'm going to Wilmington this weekend to a pull a part junkyard and I'd like to get as many parts as I can, especially if I need some wiring stuff for the taillights.

There isn't a way to get in there without the correct key. The dealer I went to required a proof of ownership to order. In fact, I didn't even drive the car to the dealership. IIRC, I showed him the bill of sale and title with VIN #. A phone call telling what you have in hand and asking what would be sufficient proof to the dealership parts department might be the most painless route. I don't know where the keys came from but they arrived the next day.

funola · #11 10-24-2011, 10:16 PM

If your trunk lock tumbler is in the horizontal position and if it is laid out like the W123, this may work:

PeachPartsWiki: Breaking into 123 trunk w/o breaking anything

ColLonewolf · #12 10-25-2011, 12:44 PM

Seems like I read once that on the SD, under the rear seat/floor mat there was a series of vacuum lines on a coupler. If you pulled them off the coupler and blew threw one it would open the trunk and if you blew through the other it would lock. Could use a syringe or something rather than trying to blow air. Just a thought but might be worth the research.

vstech · #13 10-25-2011, 02:16 PM

wait... the key works in the glove box? then I'd shoot some brake cleaner spray into the lock in the trunk, and flush it clean, then shoot a spray of wd-40 in there to lube it up. unlock the trunk, then flush it clean again with more brake spray.

bcsawyer · #14 10-25-2011, 02:57 PM

it will also turn the tumbler on the driver's door, but the door lock is not working. I spoke with the previous owner today and he said that he opened the trunk with the key I have but it was difficult.

bcsawyer · #15 10-25-2011, 04:01 PM

If the brake cleaner trick won't work, will the 123 procedure listed above or the vacuum line trick work on this car?