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  #1  
Old 08-26-2016, 12:55 AM
gastropodus's Avatar
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Location: Portland, OR
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Trunk lock unlocks with loss of vacuum

I've noticed something peculiar about my 240D: like many old 123's, the vacuum will bleed off over the course of a couple days if I don't drive it every day. BUT... while the door locks will stay in the locked position after the loss of vacuum, the trunk unlocks itself! This is a bad idea in our inner city neighborhood where thieves roam every night looking for cars to steal from.

So my question is, is this normal Mercedes behavior? Do I have to finally buckle down and chase the tiny leaks that cause loss of vacuum? My door key doesn't lock or unlock the trunk - perhaps some previous owner replaced the lock with one that doesn't match the VIN number; if I get a cylinder that comes with a key (perhaps even one that matches the VIN!), will I be able to unconditionally lock the trunk so that loss of vacuum doesn't unlock the trunk automatically?

Thank you for your advice.

Kurt

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- '79 240D - engine swap complete! Engine broken in! 28-31 mpg! Lovin' the ride!
- '86 190D (W201-126) - 2.5 NA engine, 5 speed, cloth interior, manual climate controls, 33-34 mpg (sold to forum member).
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  #2  
Old 08-26-2016, 01:13 AM
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I can't speak completely for the 240, but on my wagon the rear hatch stays locked even without vacuum. BUT, the fuel door is designed to only stay locked when vacuum is present, presumably since there's no other way to unlock it so they want it to fail open. So it could be like that, you'll just have to take a look and see how many lines are going to it.

Speaking of the rear hatch on my wagon, it turned out to be the main culprit in the lock system not holding vacuum. I removed the actuator and when I did that it now locks and unlocks so easily with the key that I'll probably never fix it. So yes, if you just take the actuator out you can use the key once you get a combo that works and never have to think about it again.

-Rog
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Old 08-26-2016, 01:27 AM
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If your key doesn't lock the the glove box, then it is likely that you have a valet key.

If your key locks the glove box, then the trunk lock cylinder has been replaced with one that doesn't match your VIN.

You can get a replacement master key (or a trunk lock cylinder keyed to your VIN) from the dealer with the title, current registration and photo ID.

The loss of vacuum will not override the mechanical locking of the trunk with a key.
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Old 08-26-2016, 10:07 AM
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My Wife recently lost my Fuel Tank Cap. So I had to reasearch on a new Cap. I did not buy one but I would swear I saw some locking Caps for W123s.

Also it looks like they sell the same caps for diesels that they do for gassers meaing that the caps have vents in them. While the vents or not needed there should be no reason for the caps not to work.

Anyway the non-locking Fuel Cap I bought from PepBoys made by Stant was $3.99.
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Old 08-26-2016, 11:48 AM
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Yes, well, let us know if a new fuel cap fixes the trunk lock issue, I'm dying to know...

-Rog
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  #6  
Old 08-26-2016, 10:16 PM
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Quote:
Originally Posted by Rogviler View Post
Yes, well, let us know if a new fuel cap fixes the trunk lock issue, I'm dying to know...

-Rog
Opps. I thought the Fuel Tank Door and the Trunk Lock were on the same vacuum circuit.
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  #7  
Old 08-31-2016, 12:19 AM
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Valet key

I must be using a valet key: it doesn't unlock the glove compartment (or the trunk). I think that I have a backup key around here somewhere that I ordered from the VIN number, so I will dig around and see if that key works in the trunk and glove box. The car is down at the farm at the moment, so further debugging will have to wait a few days.

Kurt
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- '79 240D - engine swap complete! Engine broken in! 28-31 mpg! Lovin' the ride!
- '86 190D (W201-126) - 2.5 NA engine, 5 speed, cloth interior, manual climate controls, 33-34 mpg (sold to forum member).
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  #8  
Old 08-31-2016, 04:41 PM
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Sounds to me like your key is in the horizontal position and trunk's actuator is not set properly. Is it possible that the previous owner put the gas cap actuator on the trunk upside down??

On my car, the key has two settings (vertical, where the key is used to unlock/push open and horizontal, where the vacuum controls the mechanism). It sounds like yours is definitely in the horizontal position.

When you have a chance to look, open your trunk and remove the access panel that covers the actuator. Look for how many vaccuum lines that you see connected. On the actuator, supply vacuum to each hose so that you can get a better idea of what is happening.

In the end, I spent on a $20 ebay keyless system and another $20 on 5 actuators. My keyless system works like a charm.

Also, if you manage to have the correct key, just put it in the vertical setting then you wont have to worry about it unlocking by itself. Take a pic of the actuator back there. I'm sure the good folks on the forum will be able to tell you if that is the correct one or not.

And finally, maybe the PO did this intentionally since none of the keys seem to work and they didn't want to risk never being able to open the trunk??

Before you start messing around, find out if you have a working key or else you might never open that trunk.

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