I'm preparing to replace the pneumatic regulator diaphragm in my 1972 220D this week.

I've read all of the threads I can find on the topic but I'm still uncertain how the diaphragm is attached.

From what I understand it is held in place with either a cir-clip or a cotter pin.

Can anyone help me identify where that fastener is located in this image?

I believe it is item 5 in the first picture below. Let me know if you need more info because I have this ancient Bosch document which deals with our older cars. The second pic is from the FSM, in case that is helpful.

Attached Thumbnails

   

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

Thank you for posting that first image.

The same illustration is in my copy of the factory service manual but for some reason the parts listing was omitted in the Mercedes publication.

By comparing your image with the diagram I posted it appears part number 33 is the clip I'm hunting for.

Please let me know how this turns out.. I'll be doing this same job on the same year/engine in a few weeks. BTW, where did you buy the diaphragm?

I ordered the replacement diaphragm from Mercedes-Benz of Medford through their e-commerce site, mbzwholesaleparts.com.

It was $80.60 plus $15.00 shipping.

In addition to the tear in my diaphragm, my regulator was also leaking further back.

To renew the poppet cam housing at the rear of the regulator, I purchased the o-rings from a local Bosch injection shop and laser cut a new paper gasket.

I placed the housing on a small piece of rubber sheeting in order to make sure it would seal.

It now holds vacuum, but only after adding a small plastic washer under the factory shims on the poppet cam shaft as suggested by Phil Forrest.

I ended up with extras of all the parts I used so if you PM me your address I can send over some o-rings, washers, and a paper gasket. You might try to tackle the rear housing before ordering a diaphragm. You might not need one after all.

I managed to get the new diaphragm installed today. That little e-clip is a difficult thing to remove and replace but locking needle nose pliers helped. Also, using a little axle grease will help hold the small parts inside the new diaphragm shaft while installing it.

While I was in there I did my best to renew the bracket that holds the stop start cable. The rubber isolation pads were broken in half so I used some plastic spacers from the hardware store until I can order the correct parts.

The EPC says the part number for the entire bracket is 621 070 17 40 but my bracket is slightly different as the rubber isolation bolts can be replaced separately from the bracket. I have a feeling the parts I need are very similar to the rubber bolts used in mounting an air cleaner assembly on a 300D.

Unfortunately, the car still smokes. It smokes at idle and throughout the rev range. It's grey to black smoke so I'm guessing my next project will be to test injection pump timing.

I would look into rebuilding your vacuum pump, that can cause smoke as when the diaphragm tears....it will case oil to be sucked from the engine into the intake.

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You might be right as the translucent vacuum lines are very dirty inside.

I ordered the parts to do the vacuum pump last night. I think I will try to get that done before trying to check the injection pump timing.

The following thread conveys my experiences with changing out the vacuum pump diaphragm. This may all be old news to you, but in case it is helpful....
Vacuum pump diaphragm replacement, a beginner's perspective

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

I actually read that thread last night. Thanks for writing that up.

I managed to get the vacuum pump off of the engine this morning but unfortunately the flat head screws holding the front cover on are seized.

I got one screw out and broke the head off of another. They are soaking with PB Blaster right now so hopefully I have better luck tomorrow.

The pump internals look good and I'm expecting the gasket to be leak free. I don't know why I did not perform a vacuum test on the brake booster line before I pulled off the vacuum pump. I'm not sure what I was thinking.

From what I understand, the vacuum pump draws air from the brake booster and pumps it into the intake manifold. If the vacuum pump is not functioning correctly, is it possible that this lack of air in the intake manifold would cause the engine to run rich and thus smoke?

If those screws are seized. I greatly doubt the diaphragm is in good shape. This would mean it was never replaced. Before rebuilding it, I would also read up on how to check the barrings in the pump....they are known to go bad, drop the balls into the engine and kill it...

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Your first statement is true, but no, the air added to the intake manifold is trivial compared to the air from the air cleaner. So it is not for that reason that you are checking the vac pump. If there is a tear in the diaphragm, oil can get pumped up to the intake manifold and then burn as it goes into the engine. My vac pump had tiny tears right at the big middle washers, and they were hard to see until I got the diaphragm free of everything else. But the tube from the pump to the intake was black, so that is how I knew that I had a problem that needed to be addressed.

Sorry to hear about those screws.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

Ok, now I understand.

I guess I just thought that when the car was idling and the throttle plate was closed, the only air to the engine would be coming through the small venturi hole. This made me think that possibly the additional air coming from the vacuum pump would be enough to change the mixture in a meaningful way. Guess not.

The line from the vacuum pump to the intake is quite clean but the line to the brake booster is pretty dirty. Regardless of the diaphragm's condition when I finally get it open, as you said, it's probably original and should be replaced anyway.

So now I'm kinda back to square one. For those keeping score, the car I'm working on is a recently acquired 1972 220D.

Within the last 2 weeks I have replaced both fuel filters, installed 4 fuel injectors rebuilt by Greazzer, installed new pencil style glow plugs, adjusted the valves, replaced the injection pump regulator diaphragm, and renewed the regulator poppet cam seals.

The car still smokes like crazy and I'm running out of things to try. Next up is trying to check the injection pump timing.

Pictured below is the car in question.

Noah-
Have you checked the compression? I suspect that is easier than timing the IP, so that is probably where I would head next. But I am also intimidated by timing the IP because I have read some threads where folks really struggled to get it right.

On a vaguely related note, I decided to replace the vacuum tube between the pump and the brake booster. Mine was yellow and kind of eroded on the outside, and it wasn't that expensive from the dealer. I forget how much though.

Hope you can figure out the smoking. Please keep us posted.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

When I had the Stuck Vacuum Pump Screws I think I broke 2 of them. After that I heated the Housing where the Screws Threaded in and I used a Manual Impact Wrench with a Screwdriver Blade on it that you hit with a Hammer and the rest came out OK.

In the Past People who road Motorcycles (like Myself) used the Manual Impact Wrenches.

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84 300D, 82 Volvo 244Gl Diesel