Ok, so I bought my MityVac ($25 at AutoZone) and I hooked it up to the nipple that the brown and blue line hooks up to the shutoff valve in the back of the injection pump. It didn't hold any vacuum at all. My car has oil dripping in the dash and I bet it's working all the way around the stereo area and more so 1 thing at a time though. When the weather was colder, sometimes the car would take several (5-30 seconds) to shut off, but now it never has that problem. But the oil is definitely in the line, big time. So it would seem like the shut off valve needs to be replaced, and yes I've read about to be very careful when replacing it so as to not have runaway engine problems which would ensure that my engine is trashed in the driveway.

Here's my questions,
1) Did I do the test right?
2) If I get one of those little filters to catch stuff like this earlier in the future, how do I connect them since the vacuum lines are so tiny and the filters are at least 1/4 inch?
3) Where exactly is the brake booster so I can see if the oil has gone there? What does it look like?
4) There is this yellow plastic thing on the back of the IP. Is the valve inside this (i.e. it's a plastic housing)? If so, do I need to take off all the screws, or are some of those for adjustments and I don't want to mess with them?
5) How do I access the key switch area and behind the climate control area? I already have the kick panel off, and the oil in that area is terrible, but how can I get into that side wall on the driver's side to clean in there?
6) while I'm in there, the heat at driver's feet only doesn't work, can I fix that too? I know there is some kind of servo, but what does it look like?
7) I can't find the detailed vacuum shut off replacement direction by psfred that everyone is raving about, does anyone know where that is? (Yes I've searched many times on this topic) What info I am really missing is how to check the valve once installed before starting engine to ensure the hook is hooked correctly?
8) Since there is so much oil in the keyswitch, I'm worried it may be damaged somehow. What should I look for?

I know that's a lot of questions, but this whole vacuum thing is intimidating me right now. As much info as people feel like sharing would be greatly appreciated. Thank you all!

1. It sounds like you did the test right. When you test the shutoff diaphragm, you must hook ONLY to the rubber hose that goes STRAIGHT into the shutoff diaphragm. If you have anything else such as a Y or T connected to something else then your test is not conclusive. I'm glad you've read the precautions about changing that diaphragm so I don't have to write all that here.

2. I'm not sure that a filter will do any good, the oil will just soak through the filter. I'm having trouble understanding how the vac problem relates with the oil problem, but it could just be that I've never had a vac pump fail in this way.

3. The brake booster is about a foot in diameter and the brake master cylinder mounts to it. It is right next to the fuse box on the firewall.

4. Exactly what 123 model are you working on? If it is a later 300D, or maybe a later 240D with automatic, this is used for vacuum manipulation to simulate gas engine vacuum to make your transmission shift correctly. It has no internal connection to the IP.

5. You already have most everything off that you can easily get off. You will just have to clean the best you can. While you're there, reach up behind the instrument cluster and see if you can find the oil pressure gauge supply tube. Make sure it is connected to the back of the oil pressure gauge and see if that is leaking oil. If it were loose it would soak the underdash area pretty well. This is my first area that I would suspect if there were oil under the dash.

6. I'm not sure about the heater servo. Follow the ducting that comes out at the vent that is made up partially by the knee panel. I'm not heavily experienced with the late automatic climate control.

7. What you do after you have replaced the shutoff diaphragm is apply vacuum to it as you did in your test. When you do, the stop lever should move. If it does not, then the hook on the diaphragm did not catch the governor and you then will need to try again.

8. I would just wipe down the switch as much as possible. I don't think the oil will foul the contacts. Again, make sure that your oil pressure gauge feed line is connected and not leaking. I strongly suspect that this is your oil leak under the dash.

Best of luck,

Larry,
thanks so much for the input. I feel so much more comfortable now that I understand a little more. I have an 81 300 SD, cream, and tan.

1) The blue and brown line goes straight into the valve via an elbow rubber tube connector. There are no other lines connected to this and this is the one labeled in the factory manual as going to the IP shut off.

2) the filter is just to be able to see when the valve goes bad, as far as I understand, and slow it down slightly to catch before it creeps along the line farther. Just a tool.

3)Thanks! I think I found it. Is it the big round black thing that sits behind the brake fluid reservoir? I see a line, about 3/8, threaded into this round thing, and coming off that line a few inches towards the engine is this white cylinder inline with the hose, and it has this pointed white little 'hat' on the cylinder that has a vacuum line attached. Is that the booster or the big round black thing?

4) I figured out the yellow plasitc thing is linked up with the throttle somehow, and it sits on top of the vacuum shut off. It has 2 allen key bolts to take it off and then the vacuum should be accessible. Is there anything I should be aware of when I remove this part of the throttle as I haven't done that before?

5)Isn't there anyway to take out that climate control pillar? It would sure make it easier. I did get from the searches about the oil pressure sending unit, but the SD has an electric gauge, not manual, so no oil should be present under there. It's definitely coming from the key area anyway, I can tell fom the drippage, on the accelerator area.

6) Ok I'll keep looking.

7) Is the vacuum enough strength to move that big stop linkage?

Thanks again for the replies!

1. Okay as long as there was nothing else where the vac could have leaked off except the shutoff diaphragm.

2. Understand.

3. The big round black thing is the brake booster. That large line that goes forward, goes directly to the vac pump. There should be several nipples off this line that feed vac to the various accessory circuits.

4. As I said it does not connect to the IP internally, just remove it and replace it like you found it. You may have to remove it to get it out of the way to replace the shutoff valve.

5. I didn't realize that you are working on a 126 car. I know that this is a HUGE task on a 123 and I assume that it is equally daunting on a 126.

6. This could be different on a 126, but you still will just have to look for the flap and actuator.

7. Yes, if the shutoff is hooked in properly the mity vac will make enough vacuum to move the stop lever. When you hook the shutoff in place, you need to move the stop lever in order for the hook to catch it. Experiment until you have it in place and vac will move the stop lever.

Good luck,

Yesturday, after looking at the vacuum lines and following them, but not disconnecting htem, now my door locks don't work Where should I look first? I know I should look for obvious cracks etc. Does the big white vacuum line lead to the doors? Or is it something else because doesn't the 126 have a separate pump for door locks? Is everything failing at once? AHHHHHHH!!!!!

Again, I have to plead ignorance re: the 126 chassis, but I think it has an electric pump like a 124 car. If so it is probably under the back seat.

On a 123 car the line at the firewall that feeds the locks is yellow with a stripe.

Good luck,

1. vucuum pump on 126 is in the area of the trunk, electrically
powered for the locking system ONLY!

2. There is a separate engine powered vacuum pump for all
other functions.

3. If you have suffered an Injection Pump shutoff failure
(not a big deal to replace the Vacuum powered shutoff)
there is the possibility that the vacuum has pulled the
sump oil (which lubricates the I.P.) as far as the A.C.
system controller AS WELL AS THE VACUUM POWERED
IGNITION SWITCH.

4. I had the very same problem with an '84 300SD.
(engine oil leaking from the upper console; I lost it!)

5. Problems correctable with patience , even if it doesn't
seem so at first!

Looks like Compress Ignite is giving you some valuable info that is more specific to your particular model than what I am able to offer.

Good luck,

drum roll please.......
there is oil in the t back in the trunk!! Well, I'm expecting my part from Phil very shortly so I should be able to fix the shut off valve problem, but in the meantime, I think I should stop the oil floating around. Can I plug something off so this doesn't happen? How bad is is to drive without vacuum? I think I need it for the tranny right? And how in the world idid oil get into the locki system? Isn't it a completely separate system in the SD? I need an SD expert to explain this routing...
and by the way, how do I remove the riveted in trunk side liners? I've popped half them through stuidity.

can someone please tell me how oil got into the locking system of an SD?