300sd doors won't unlock - Page 2 - PeachParts Mercedes-Benz Forum

coolram62 · #16 11-04-2014, 08:08 PM

One thing to keep in mind is you want to stay away from spraying any type of petroleum based product in a lock. Brake cleaner can be an exception since it disapates so easily. Always use an aersol graphite product on locks. Do you know if you vacuum pump has ever gotten wet. The one in my '83 SD had to been using a snorkel when I first bought her. The interesting thing is how MB used a feature basically 10 years ahead of most others in that the driver's door not locking without the key with the car off.

ROLLGUY · #17 11-04-2014, 08:18 PM

Quote:

Originally Posted by angst

I now know that there is electrical and vacuum lock on the trunk and the electrical will not unlock even if the vacuum one does if the alarm has been triggered. It all seems pretty consistent with the symptoms. When the locks do all unlock together I can hear a moment of air noise but no mechanical noise.

I had the exact same problem with an '85. I had to unscrew the strike plate on the electric locking unit to get the trunk open. If you somehow can get the trunk open just enough to use a 10mm wrench on the bolts, you can release the strike from the latching mechanism. It took a while for me to do it on mine, but I eventually got it. I permanently removed the strike from the trunk lid so this would not happen again.....Rich

eatont9999 · #18 11-04-2014, 10:24 PM

The understanding I have of the early W126 trunk lock is that if you use the key in the position I mentioned before, the trunk will open regardless of the vacuum system's position. Assuming the 84 is the same mechanical lock with an added solenoid-actuated lock with a separate latch, it seems to me that if you can actuate the solenoid, the trunk should open with a master key. Solenoids usually operate with 12v, so find where the solenoid gets its 12v and see what you get when voltage is applied.

To answer the OP's earlier question about being able to apply vacuum or pressure to the vac lines under the carpet to open the trunk lock: yes, I have done that before. I have not run into the alarm system on later models, though. On early model W126s, I have had to drill a small hole next to the lock to push the trunk latch to open the trunk. I only have to do that when I don't have any keys to the car - IE: junk yard.

SD Blue · #19 11-05-2014, 12:37 PM

Quote:

Originally Posted by angst

SD Blue
Can't wait to try your suggestion in the morning. Is that technique a secret?
There is a wire on that harness that some PO put on there that could have been used for this purpose. It has continuity to ground.
eatont9999
Thanks I hadn't seen that link. There are a lot of other threads referenced in that thread that look like good research for this evening. An interesting approach in one of them a guy built a rod tool out of a bamboo stick and was successful going through the first aid box. That was a w123 though. I have seen more than once in searches that it wont work on w126.

Will read on. Im encouraged that im on the right track now to getting it. I now know that there is electrical and vacuum lock on the trunk and the electrical will not unlock even if the vacuum one does if the alarm has been triggered. It all seems pretty consistent with the symptoms. When the locks do all unlock together I can hear a moment of air noise but no mechanical noise.

I sent the procedure as a PM to aid in making the information "need to know". If I post it in the open forum it can be searched by Google and others and lets every ne'er-do-well have easy access to how to break into the trunk. Others may think it is over-cautious, maybe even futile, but I think it is worthwhile to try.

angst · #20 11-05-2014, 12:53 PM

Quote:

Originally Posted by SD Blue

I sent the procedure as a PM to aid in making the information "need to know". If I post it in the open forum it can be searched by Google and others and lets every ne'er-do-well have easy access to how to break into the trunk.

If a criminal had access to the alarm it means they already have access to the cabin. If they don't have a key then nothing that is done to the alarm is going to make the trunk open without a key in either the driver door or the trunk door. Right? Heck, mine wont even open with the key. A thief looking to get in the trunk would brute force it with a crowbar in seconds and not pre plan it with an internet search for threads in a forum to find out the intricacies of how the locks work.

Thank you for the tip regarding the alarm. I have messed with it for an hour today with no luck. Ive tried all sorts of combinations of starting with a door locked or unlocked. engine running or off.
The locks are back to not unlocking other than a momentarily whir that can be heard in the trunk. The alarm will still start clicking on some sequences. Im still not sure what triggers the alarm.
Ill send you a pm to see if I am doing your recommended technique correctly.

UPDATE 1:40pm A few more cycles of brake cleaner and then graphite powder in the trunk lock and I was able to turn it horizontal. Yeah! the trunk is open.
When I leave the trunk open and key lock and unlock the driver door the latch inside the trunk seems to be locking and unlocking appropriately. Im not sure where I go from here. I don't think I dare close the trunk. ha.
Now that it is open what can be done to prevent future problems? Disassemble the lock and give it a tune up somehow?

toomany MBZ · #21 11-06-2014, 07:42 AM

A locksmith once told me to not use graphite in any lock. Most folks do this routinely, the graphite builds up and seizes the lock.

Use the spray lubricant of your choice.