Trunk Locking itself?

[NalgeneSF]

Trunk just seems to randomly lock itself after being opened and closed a few times. Never touched the key, just pushed the button and pulled and nothing happens. Tried spraying some wd40 in but to no avail. Any suggestions?

[NalgeneSF]

If it helps, the vacuum locking has a leak I haven't been able to diagnose yet.

[Randys01]

Irrespective of vacuum system leaks, if you open /unlock the driver's door then all doors and flaps assume the open position. The boot however  has a manual lock overeride via the key. You should be able to lock and unlock the boot with  the key.
There is no way the boot vacuum actuating system can come on and lock the boot by itself/randomly/intermitenetly.
Try totally depleting the vacuum resevoir by operating the lock/unlock function until it is exhausted.
This will set everything at the unlocked/open position. Try the boot. If it is locked try the key.

[revilla]

As stated above, vacuum not working properly doesn't explain your symptoms. The problem is rather related to the locking mechanism inside the trunk. Sometimes is either a weak spring (there's only one there) a bent rod, a bent base, a worn out plastic/rubber pusher.  I'd open the lid (4 screws) right under the lock. Take several pictures to facilitate reassembly, not very intuitive. Disconnect both vacuum lines. Move the main rod left/right. Understand how it works. Pay particular attention to the pusher that only acts in key open position (turned left). It's a hit/miss situation. If the assembly is bent, misaligned or wobbles it'll miss the "push". I bet your problem is coming from that. Happens often on these W116s. The fix will depend on your observations. There's no one "fix-all" solution.  WD40 won't hurt BUT RARELY fixes the problem (a bent rod for example will laugh at oil).
Please let us know so we can guide you through the right direction. Pictures and understanding of the mechanism is key here as is mandatory in anything related on this hobby.
Please let us know.
Good luck.

[NalgeneSF]

Okay, will update when I work on the car tonight, but my symptoms are this: doors are all unlocked but I have a vacuum leak somewhere in the system. I blocked off the vacuum lines leading to the passenger compartment, so that I would have better vacuum on the engine. I confirmed that my drivers side door lock is in the unlocked position, and I have fully unlocked the trunk. To normally open the trunk (I always left it unlocked), I would push the button and release. Now, after not doing anything to it, it has locked itself. The button moves in and out great, and the key has no trouble turning. I can push the button in and pull to open the truck, but it stays locked. @revilla, you're saying that I should open the lid under the lock? I am still unable to get the trunk open, so that will be my first move after getting this to open up.

[Alec300SD]

To unlock the trunk when vacuum has been lost, insert square head master key in trunk lock, rotate key fully counter clockwise to the stop,
and then (while the key is still in the full ccw position) push key and trunk button inward to release the trunk latch.

If this doesn't work, then there is binding in the lock assembly.
Downward pressure applied to the trunk lid is sometimes helpful to relieve binding in the latch mechanism.

[NalgeneSF]

Okay, got the trunk unlocked by pushing down. Thank you @alec300sd! I've attached a video of what happens when I push the button in, and recorded what the lock looks like. Anyone have a good idea of what is happening? I think that clip inside the trunk latch is supposed to move forward when the button is pushed, but is no longer doing so. I tried to attach a video but the file size is far too large. Attached are some photos of the mechanism.

https://imgur.com/a/QWQ76Ut

[NalgeneSF]

More photos... I think it is because this knob here is smashed... any solutions on how to fix? I'm thinking of throwing on a rubber head or finding a washer.
https://imgur.com/a/QWQ76Ut

[rumb]

I'd fix the vacuum leaks on the interior first and see if that fixes things.  The plunger looks worn but not enough to cause issues.  It's the position of it, not the length that is important for the lock to remain unlocked.

[NalgeneSF]

I'd prefer that the trunk doesn't lock itself unpredictably like this though. It just seems strange that the plunger doesn't push on the rod even though it seems to turn just fine. You think it is coming from the vacuum leaks?

[rumb]

Im wondering if the vac rods are not aligned correct because your vac lines are disconnected?
I'd think your just going to have to get in there and try a few things.

[NalgeneSF]

Okay, I've done some testing and confirmed that it is the pusher sliding off the rod. How best to solve this? Im thinking of putting a bunch of heat shrink on it to make the surface more grippy?