Hello,

I imagine that one of you is reading the title and immediately thinking "obviously its a vacuum system issue, classic W123".
So a couple days ago I noticed that the doors were not locking on my 1977 240D.

I can put the key in the drivers side tumbler and feel no resistance as I turn the key CW and CCW, this does not actuate the door plunger at all.

On the other side (passenger), I put the key in the tumbler and feel it get "stuck" as I turn it CCW to lock it, still will not actuate the plunger, but I can see it twitching as I try to lock it from the passenger side.

When I am driving, say, on the highway, and the engine is running, I can push the plunger on the drivers side door down and it will lock all the car doors. As soon as I turn the car off, I can no longer manually actuate the doors.

I am pretty sure this is a vacuum leak, but I have not dove deep into it yet. Has anyone had experience with the symptoms I am experiencing who can point me at either a part or a section of vacuum tube to check?

ALSO: What is the best tool for diagnosing vacuum problems? Is it a simple hand pump I can get off amazon? Should I splurge for an electric vacuum pump? let me know.

thanks,
Jhu805
1977 240D 4-spd Burgundy Red

Update for anyone who may be experiencing the same issue:
Took off the drivers side door panel and manually moved the master vacuum switch, was able to lock the entire car by doing it.
I determined that the problem was with the door lock itself, so I took that out of the car and found that a white delrin cone had broken off. See pictures for reference. Aint a chance in heck that I can fix it without it breaking again, currently in the process of finding a replacement cone.

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I recall there are a few threads about this here.

On my 300D this part is really worn and deformed on the driver’s side. I used heat to straighten it out. My cars are both opened with remotes so I never use the key to open the door. If I did they likely wouldn’t last.

That is an odd looking part and I don’t think you’ll be able to get it by itself new. Your best bet is hitting the junkyard and getting one there.

It’s such an odd shape. I wonder if there is a way to make something to replace it that has simpler geometry.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

My solution was to find a 1979 W123 and salvage the door latches from it ~ they have a pot metal piece here, this plastic one often breaks as Germans pioneered the use of bio - degradable plastic beginning in the 1960's .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I talked to the guy that did a 3d model for this part.

You can get a printed version here for lots-o-money

mods.... please remove link if against rules


https://www.shapeways.com/product/M36WSAQ7H/metal-door-lock-assembly-piece-for-w123-mercedes?optionId=11461985&li=marketplace

THANX ! they also make W123 ~ T alignment wedges for the rear hatch , I need a pair .

Lots of nifty W123 models as well .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Wow that 3D printed part is awesome. It’s metal.

The design looks easy enough…just a bunch of cones and cylinders. The metal is the difficult part. I notice there are a bunch of services in China that will take a 3d file and print it up in metal for an inexpensive price.

https://3d.jlcpcb.com/

$45 sounds about right. He has to make some money for his efforts.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

I’ve been thinking more about this part.

Looking at how it works makes me wonder why it is that shape. It’s hard to make. I suspect it’s an anti theft feature. It looks like you can do the same job with a simpler geometry if you don’t care about anti theft.

It may be possible to redesign the part so it is very easy to 3D print without the mechanical weaknesses of a 3D printed part.

I think I’ll grab a couple of door locks next time I’m at the JY.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

I was in my storage room yesterday, and I have a lot of 123 doors and door parts...
Been sitting inside for 20 years...
I could check next weekend if I have one.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I actually found that part on Shapeways, but it was for the passenger side. I messaged both the shop owner and Shapeways to see if they can mirror it for the drivers side, but I got no reply from either.

I ended up getting out the calipers and modeling and printing the part myself. I attached a photo.

I am going to test it out today, see if the part will fit in the door and actuate (not put any real force on it). If it works well, then ill get this made out of either metal or glass filled resin.

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Nice work. I wonder how hard that would be to get cast out of a low temperature zinc alloy. I’ve seen ones that can be done in silicone molds.

Does it really need that cone shaped interior? That makes it weak for 3D printing in plastic. It’ll separate along those layer lines on the thin spot eventually.

I wonder if you can get away with a thicker wall. It seems like it can be redesigned to be 3D printer friendly.

ETA - hey I take that back about home casting. Pewter would be a low temp metal that can be cast in silicone. But, I just looked at some of the prices at JLC 3D printing in China. This thing will likely cost less than $20 to print in stainless

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

Update from my 3d printed door lock plastic piece.
I put it in the drivers side door and it actually works really good.
The weak PLA Filament part is actually holding up with the key and all the forces to actuate the door lock.

Maybe ill order a metal one online, maybe ill just purchase some glass filled Nylon 3200 for the 3d printer!

Heres a link to the .stp file if anyone has a CAD program.
https://www.dropbox.com/scl/fo/otauww4ofbuq7jzc8tgei/h?rlkey=d5nwsxhyuzwjmz70djesu62ja&dl=0

Hey thank you for sharing that. That’s great that it works in PLA.

Is the passenger door just the mirror image?

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

Jhu,

I just printed this out. PLA+, 210 deg C, 100% infill with a 0.28 mm layer which works well for strength on my Creality Ender 3 for some reason. $0.20 of filament. 1 hour to print two.

Anyhow bottom line, your part is strong. I twisted it hard at the likely places I’d expect it to crack like the little tang on the end of the lever and on the cone section. This thing won’t break under the loads from the lock. It may get weaker over time as it gets heat cycled and vibrated. However gentle heat cycling seems to make PLA stronger over time.

I made a mirror image one. I assume the passenger door needs the mirror image?

Very impressed! Thanks again for sharing this.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

Wow, that's amazing C .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better