Hello, on my 84 300d I have been having some hard up shifting. I fixed a few vacuum leaks I found which helped a little but still shifting quite hard. I tested the main line at the brake booster and found a very erratic vacuum jumping around to 22 hg. I also am finding oil in the vacuum lines. Does this sound like a check valve issue? Or more like a worn out vacuum pump?

If you remove the main Vacuum Line at the Vacuum Pump you can unscrew the Check Valve and look in side and see if the Parts are still there.


I can't recall anyone posting they were getting pulsating vacuum before so I can't comment on if that is an indication of a Check Valve Issue.

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84 300D, 82 Volvo 244Gl Diesel

Quite often for some reason the check valve begins to disintegrate which may be causing your problem. A new valve is around $75. If your car has more than 250,000 miles you also may want to consider a new vacuum pump as a general maintenance item. Vacuum pumps can explode internally taking major parts of the engine with it. Cheap insurance to change the entire pump.

Oil in the vacuum lines may be the transmission modulator leaking. I might check that first.

If the issue happens to be with the vacuum pump - check out the below link to our DIY fix on it. If you have any questions on the procedure, feel free to post a Comment just below the article and we'll do our best to give you specifics.

Mercedes-Benz W123 Vacuum Pump Replacement | 300TD 1977-1985 | Pelican Parts DIY Maintenance Article


-Dmitry

I likely missed some info. I think if you are checing the main line Vaccum to see if it is the Vacuum Pump or Check Valve you ought to disconnect the rest of the stuff and cap off where those hoses were so that will not influance the test.

There could also be a leak in the brake booster that might not be bad enough to effect breaking but bad enough to cause the other issues.

When my Engine would not shutoff I had low vacuum in the main line. I removed the check valve which in my case had not come apart and hosed the inside out with WD-40 (don't use Brake Cleaner) and that fixed the issue.

I am trying to post a pic of a Vacuum Check Valve that came apart. Sometimes the parts fall inside out of site but don't cause damage because there is another valve that keeps them from going into the pump further.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Thank you, I'll look at the check valve and see if it looks OK. I did change the rubber hose right at the vacuum modulator and there was no sign of ATF in there. The oil seems to be in the 3 way connectors that are around the oil filter housing, and also in the main line when I disconnected the brake booster. I haven't noticed any brake fluid loss.

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1984 300D Turbo 200K

Oil in the lines is often from the "shutdown valve" on the rear of the injection pump. It's brown tube runs to a vacuum switch at the "ignition key". Another brown tube runs to the main vacuum source. Don't mix up the two tubes (colored stripes, forget which). Best to plumb a small clear filter in-line w/ the shut-down valve so you can see when its rubber diaphragm fails and sucks oil thru. That is better than waiting until oil drips on your right foot. You can buy such filters as fuel filters for lawnmowers. Some VW shops keep them in bins. A similar clear filter is factory, in the black vent tube between the cabin and the VCV (on top of IP).

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

To update this situation, the check valve was still intact. The shifting problem turned out to be due to a restriction in the first port that runs off the main vacuum line to the modulator. I reamed it out with a 1/16" drill and now it shifts normally. I haven't been getting any oil in the new vacuum lines I installed as of yet. Everything in the vacuum system seems to be working now.

FWIW ;

that primary vacuum pipe has two nipples on it, the first one is 0.6 and the second is 0.5 ~ since the tranny doesn't seem to need a lot of vacuum I run the first 0.6 nipple to my key switch (brown) and HVAC (green), the tranny shifts great and the HVAC comes on nearly instantly and the engine stops before I can withdraw the key plus it's very difficult to stop the engine my hand under the hood .

It seems every 123/126 I see has different routing of the vacuum hoses and pipes .

The tiny black cabin vent pipe with the clear screen it, goes to the side port of the white VCV on the top of the IP, correct ? .

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-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

Yes, the side port on the VCV is hooked up to that vent line. On top of the VCV is the green regulator, connected to the transmission and supply line from there.

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1984 300D Turbo 200K

Thanx ~ just checking to make sure as i was replacing the IP Wednesday and managed to unhook more vacuum lines than I meant .

This car ('84 300CD) came with a gasoline i6 hose map decal on the core support....

It seems to shift fine and the HVAC and shut off work well so I think (hope) I reconnected everything properly .

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-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