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'73 450 SEL Vacuum Central Locking

Started by C.Lindon, 01 July 2020, 04:50 PM

C.Lindon

Hello all,

New member here with my initial post.  I inherited my father's '73 450 SEL a number of years ago after it sat for most of the last 20 years of his life.  I know that sitting unused for an extended period of time is the worst thing that can happen to a car and yes its condition reflected that.  I knew that it would have problems but there were more than I could have ever expected.  Nevertheless over the few last years I have sent it through a thorough mechanical rejuvenation first at the local Mercedes dealership and then at a respected aftermarket German car specialist shop
and no Mercedes will never see this car for service again!! I then had a complete repaint done with any necessary underlying body work being addressed so it is now in quite good shape.  Not concours level but certainly very very good.  There are of course a few remaining niggling issues, especially with the electrical as can be expected with a 47 year old car and I am continuing to work on them.   

Of particular relevance right now is the vacuum operated central locking system.  Plain and simple it is not working at all and in truth it has not worked properly/reliably since the mid 80s.  Is there a consensus on typical failure points and how to address them?  Given my own choice I'd ignore it but Quebec requires that we lock our cars when parked in public so I need to get it functional for the odd occasion I do park on public lots or at the roadside.

Any guidance would be much appreciated.

Thanks and Cheers
Carl

ptashek

Hi Carl, and welcome.

The vacuum central locking is a weak point on these cars. There can be multiple causes of failure, in no particular order:

- cracked diaphragms on the actuators
- dried out / hardened seal on the vacuum reservoir under the parcel shelf in the trunk
- broken vacuum lines (if the cars sat for a long time, maybe rodents had a go)
- leaking master cylinder in the driver door
- leaking rubber connectors on the rigid vacuum lines

The diaphragms are an easy fix, but pricey. Last time I've checked they cost ~14USD/each.
The hard lines I believe are at least partially available from MB still.
The rubber connectors are just standard vacuum hose, I think 5mm ID  (I'm sure someone will know exactly).
The master cylinder is still available from MB, and also cheaper as an aftermarket option. So is the reservoir seal.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

rumb

Start in the drivers door and see if vacuum holds on the master switch. then go door to door and check the diaphragms. A miti-vac with gauge can be used to see what holds vacuum. Dont forget the gas door and the trunk.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

revilla

Welcome to the club Carl.

There's a key first question: does the lock system operate with the engine running? Or not at all?

The answer to that will determine the course of action.

There's one level if the system is simply not holding pressure, but things can grow significantly in complexity if it isn't even working with engine running.

In any case, one VERY usual suspect and VERY easy to test are 3 little check valves on the engine compartment right next to your fuse box. I ALWAYS start there, one because is the 'root' of that vacuum system and two because the probability is HIGH they are shot.  I bet they're blocked so your system is not even seeing vacuum at all.

They look like little barrels with in/out nipples. About 10mm in diameter and about 15mm long. Colors vary but either blue/black or white/black.

I would simply disconnect all of them, reconnect the lines, run the engine, driver window down, close door  and test pulling up/down the driver's door lock.  Have a seat, you might be surprised of the results.  But don't get excited just yet as the fun is just about to begin if your system is not holding pressure.

Please let us know of the results so we can help you further. 

Cheers

This is how they look like:

https://www.google.com/search?q=checkvalve+w116+vacuum&rlz=1CDGOYI_enFR862FR862&oq=checkvalve+w116+vacuum&aqs=chrome..69i57.20383j0j7&hl=en-GB&sourceid=chrome-mobile&ie=UTF-8#imgrc=ByX6TujOut2ueM






C.Lindon

#4
Thanks for the welcome gents.  While the vacuum central locking was innovative for its day, yes it is inherently problematic and increasingly so as it ages.  I thought I had rid myself of vacuum accessory problems with the demise of my brother's 67 Thunderbird and its vacuum operated headlight covers and breakaway steering column - obviously not the case  :( ::)

In my case the central locking system doesn't work at all, engine on or off, so I think Revilla's guidance is the first to follow and then Rumb's about the driver's door.  Through the mid 80s and into the 90s the system became "quirky" in that it would not lock from the drivers door.  Dad would have to close the drivers door and then reach in from the rear drivers side door to press the locking knob down at which point it would all lock and would be fine until the next locking cycle.  Clearly sitting from about 1992 - 2014 without much use helped everything dry out perhaps exacerbated by dirt accumulation.  And Rumb, while I remember the trunk is[art of this system thanks for the jog about the fuel tank door - I didn't even think of that because I have no memory of it working even as a kid but I just checked the car and there is indeed a hole in the door that lines up with a hole in the housing which would be just right for a locking pin. 

Anyway, I'll report back as I get the chance to investigate - mind you don't hold your breath for immediate progress -  but I'll certainly remain open to further suggestions and your "war stories" with this system.


Thanks and Cheers
Carl

ptashek

Quote from: C.Lindon on 01 July 2020, 10:58 PMThrough the mid 80s and into the 90s the system became "quirky" in that it would not lock from the drivers door.

That's a smoking gun pointing at the master cylinder / switch in the driver door.
This is the part you're looking for:


Quote
with a hole in the housing which would be just right for a locking pin. 

So there's no actuator for the fuel filler flap? Could be another point worth checking, especially on how the hard line that would normally go to it is terminated.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

revilla

Excellent Carl, keep us posted on your findings, even if it takes some time.

Priority 1 is to ensure you're getting vacuum supply to the system, starting UP UP UP stream at the vacuum source. Once that's secured, let the vacuum leaks hunting begin :)

The analogy is like working on fixing a carburetor without ensuring first fuel supply from the pump. I've seen that and it's not fun seeing people 'playing roulette' changing parts hoping it'll miraculously fix the problem.  However, if the hobby is to change parts for the pleasure, I can understand that too.

Upper diaphragms are on the top of my list as next suspects. FYI, I fixed several vacuum switches for literally cents using 4 o-rings that replace the conical rubber pieces inside. Fun little weekend project.  So far no failures (yet :))



Cheers




C.Lindon

#7
Quote from: ptashek on 02 July 2020, 04:25 AM
Quote from: C.Lindon on 01 July 2020, 10:58 PMThrough the mid 80s and into the 90s the system became "quirky" in that it would not lock from the drivers door.

That's a smoking gun pointing at the master cylinder / switch in the driver door.
This is the part you're looking for:


Quote
with a hole in the housing which would be just right for a locking pin. 

So there's no actuator for the fuel filler flap? Could be another point worth checking, especially on how the hard line that would normally go to it is terminated.


I came across comments about the driver's door master cylinder years ago when dad had made made overtures about trying to sort out the locking system.  But he only ever took the car to Mercedes dealerships and the cost of them going on an invasive "hunt" around a "minor" system was just too high.  Thanks for the re-prompt about it and any chance you have a part number readily at hand?

Yes the actuator for the fuel door lock is in the car, just hanging loose in the quarter panel.  It is yet another legacy of things not quite going back together properly after the 2016 repaint.  While this was by far the best of the three repaints the car has had thee are quite a few niggling things that were not done or re-assembled quite right.  In the end it is easier and fast just to sort these things out myself than "bang heads" with the body shop.  One more little task for when the system as a whole is working better.

Thanks and Cheers
Carl

floyd111

Do the cops really care, check and fine people for not locking cars. in Quebec?

C.Lindon

Quote from: floyd111 on 02 July 2020, 01:54 PM
Do the cops really care, check and fine people for not locking cars. in Quebec?

Not the cops but Bylaw Enforcement sure do.  Last year I got a ticket at 04:00 hrs because my wife's car was parked on the road in front of our house with the doors unlocked! Downright creepy that someone is pulling car door handles at that time, but then again we are Anglos in a french province where our only value is to pay taxes and tickets.

ptashek

Quote from: C.Lindon on 02 July 2020, 09:28 AMThanks for the re-prompt about it and any chance you have a part number readily at hand?


This PDF has the complete parts list for the central locking system. Actuators, hard lines, check valves - the whole lot, with pictures :)
https://www.dropbox.com/s/fbs0gt4lb3bkcao/C116032_CentralLocking.pdf?dl=0
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

rumb

Quote from: C.Lindon on 02 July 2020, 06:25 PM
Quote from: floyd111 on 02 July 2020, 01:54 PM
Do the cops really care, check and fine people for not locking cars. in Quebec?

Not the cops but Bylaw Enforcement sure do.  Last year I got a ticket at 04:00 hrs because my wife's car was parked on the road in front of our house with the doors unlocked! Downright creepy that someone is pulling car door handles at that time, but then again we are Anglos in a french province where our only value is to pay taxes and tickets.

Some States in the US you could probably shoot someone if they tried getting into your car.  :o
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio