Had the classic hard brakes, no shutoff with key and lost doorlocks yesterday in my W116 300SD. I check all my vac connections and they are good, so I moved on to the check valve on the vacuum pump and saw this. Is it just an opening passage the whole way through. Is this normal, or should there be some kind of check inside there? I'm seeing check valves elsewhere that have something inside them.

My valve:

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'80 300SD - '83 240D - '00 E55 AMG - '02 G500

its been a while, but I recall that there should be a rubber diaphragm in the center of the valve.


Otherwise, the pump would probably have a hard time building up vacuum.

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1983 300CD Turbodiesel

I might have a spare if you need it. But they should still be available from MB.

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1983 300CD Turbodiesel

https://www.pelicanparts.com/More_Info/0049971872.htm?pn=004-997-18-72-MBZ

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1983 300CD Turbodiesel

Yepp. I guess that’s what I need. I guess those missing parts are in the bottom of my vacuum pump then.

might be a great time to refresh the pump also. rebuild kits are scarce, but you may get lucky.
stretch/army has a great write up on the pump internals.
entertaining read.
More than you are likely to ever want to know about OM61X piston vacuum pumps

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1983 300CD Turbodiesel

Probably not. I would suggest that you try to fish the broken parts out of the inlet with a magnet and/or piece of wire. That's always worked for me.
The reason for the vacuum problem is that the missing parts are blocking the inlet. The check valve is not necessary for the pump to operate; it's there to prevent oil from being sucked into the vacuum plumbing when the engine is not running.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

If this is your SD (and it is like the 126), the failure of the engine to turn off is not related to the door locks. You have a separate pump in the trunk which runs the locks. There is a junction box beneath the carpet in front of the passenger seat (front seat). The plastic lines can be tested there to see where the leak is happening. May be an actuator in one of the doors. Easy replacement to remedy door lock problem.

On a W116?

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Actually I do not know. I am guessing that it is like the 126. Maybe not.

All vacuum is run of the main pump on the w116.


There is a three way vacuum switch located on the driver side door behind the door card, there is a reservoir under the hat shelf opposite side of fuel flap, accessible form the trunk, on top of the fuel tank.

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Nosce Te Ipsum "Know thyself"

I've never heard of a separate vacuum pump running door locks, but that explains the weird buzzing noise I sometimes hear in the trunk of my roommate's W126. It's definitely not there on a W116.

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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles

Yes, I just assumed a 116 was like my 126 - but not so.

On the Piston type Vacuum Pump when the parts dump out of the Check Valve the drop down into a passages. At the open end of the passage is a Disc Valve and the Check Valve parts are too large to pass into the Valve.
In the past people leave the check valve parts (in the piston type pumps) inside and they don't remember anyone saying they caused an issue.

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84 300D, 82 Volvo 244Gl Diesel

Fact is, there have been numerous instances of intermittent vacuum failure reported on this forum, all caused by check valve components rattling around in the vacuum pump inlet.

Here is one:

Intermittent Vacuum Problems

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.