I have a 80' 300D with the old style pump. My car blows out light grey smoke on idle and alot more when acceling from a red light. The car shuts off If I rig the door lock vac switch. But no leaks in door lock system. I get about 19 reading on the vac guage. Is the diaphram leaking, is that why the smoke is coming out? should I upgrade to a newer style pump?is it possible?

My first MB was a 300CD. Needed some TLC. Alot of vacuum stuff not working properly. Came time to change the air breather element. Found the inside of the breather moist with oil. Not much though. Being a diesel I just thought this was normal. After about 1000 miles on the clock the car would not shut down with the key. Found the stop button under the hood.
Researching the vacuum system and tracing the lines I removed the air breather lid and found a pool of oil along with my new breather element soaked in oil.
I dismantled a similar car at the junk yard to locate everything I needed to look at involving vacuum. That lead me to the vacuum pump up front of the engine. I discovered the cause of my problem was a severed diaphram. So I collected a few good ones and returned home to clean up my oil soaked CD. After cleaning the dashpots, blowing out the lines and putting in a better diaphram, all my vacuum devices worked!
You need alot of patience during the cleanup. But you will be glad when it's fixed.

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i dont want to steal the thread. i just worked on my 240D's vac pump also and it makes an odd sound now. i have a newer vac pump like what is in my 300D, and if i cant figure out what is wrong, then i might want to switch also. if anyone knows how the small round valves are supposed to be inserted, or has some pictures of their pump, then it would help a lot. could that sound come from one of the valves being in there the wrong way? i should have taken pictures, and i may have to now, the next time i take it appart.

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Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

I went through this last year on my '80 300 TD. It developed lots of vacuum symptoms (no shut off, no brake boost, no door locking, funny shifting) so I opened up the vacuum pump and found the diaphragm had a quarter-inch hole. I didn't observe the position of the check valves while disassembling, but by looking at the tubes that were connected to the pump I figured out which way it sucks (It sucks a vacuum on the line that goes to the brake booster.) and by looking at the valves I could tell which way each one should face. I tested them by sucking and blowing by mouth and found them both functioning. It's still working. Steve

well it turns out that the previous owner was an idiot. he tried to fix his vacuum gremlin with the wrong size rubber vacuum lines. they are way too big and there is no way for them to hold any vacuum. so i took some lines out of my 300d just to test my theory and the car works great again. i went to autozone to buy more, and i will spend some quality time replacing all the vacuum lines in the 240D. either way the diaphram had 2 holes in it, so it was good that i fixed that, but bad vacuum lines make it real hard on the vacuum pump. so if anyone needs a newer vacuum pump, i bought one from a forum member for $50 that is for sale again.

80300Dbenz,

what do you mean with "rig the door lock vac switch"

no leaks in the door lock system is good. does your car only have the smoking issues? if it turns off, and you have no leaks, and if you have an automatic that shifts fine, and it holds a 19, then i would not suspect a bad vacuum line.

i can notice smoke off a red light if i push it somewhat, but that is normal. i am not sure about the color, and another member would have to help you out.

if you could spell out your symptoms more, then we can start eliminating your problems and locating your problems to check out more.

if you need an old style pump, the guy that i bought my $50 vac pump from, has a old style for only $30.

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Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

Sorry for the hijack. This thread makes me think about my own car I'm just getting into. I have oil in the vacuum lines in the dash. Does it always mean a bad pump? I have a theory about my own situation:

Mechanical oil pressure gauge leaks and blows oil everywhere inside the dash. PO doesn't get to it before the oil gets all over the two vac lines at the ignition switch. Those rubber bits swell and leak, and suck in oil. Those lines go to the four-way connector under the hood, where the climate control and door locks meet it. Those lines also become contaminated (though the yellow check valve protected the locking system). So what you end up with it a bunch of wrecked rubber vac parts and a few ruptured diaphragms in the climate control mechanicals. Does anyone disagree with that reasoning? My pump pulls a 20+ or so on my vac gauge at idle, and I have everything mostly working now. I feel like I should get all the oil out of there before putting in new rubber, or I'll be sorry. Any tricks for doing that?

Thanks,
Jerry