I have a friend with a 1980 w116 300sd-- he has the dual diaphragm type vacuum pump. The pump seems to be pulling about 1/8 what it should ( we pulled everything off the pump to test it) -- also the needle on the vacuum gauge jumps in time with the engine.

The car does not smoke or shift badly-- it makes me think that the pump has not completely failed. how hard is it to fix this pump? Can he buy a rebuild kit for it- and does this mean removal of the radiator to do the job? It sort of looks that way by the layout under there.

How insane is it to try to fit an electric vacuum pump as a quick/temporary fix?

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1967 250SeC
1979 450sel 6.9 (usa)
2009 S550

I'm curious as to the answers to your questions, since I also have a W116SD. What kind of vacuum readings are you getting? If it's only putting out one eighth then I'm surprised your brakes are still functional. I'd suspect one of the valves in the pumps given the symptoms but I don't know if they are available separate from a complete rebuild kit. What symptoms got you digging into the vacuum pump?
I was able to rebuild a different early style pump on my 77 300d without removing the radiator but the 116 has a different pump.

Just looked at mine. I think the pump can be rebuilt without removing the radiator. The shroud will have to be removed I think. However, the whole pump will have to be removed to access the lower diaphragm and check valves. On my 77, I could replace the diaphragm and valves without removing the whole pump.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

They are functional, but no boost, so you have to use your muscles to stop the car, old skool style.

the engine also has a hard time shutting down. You can rev it up abit, then turn off the key, and that sometimes will generate enough vacuum to shut down. whew!

I looked at some diagrams, it looks like removing that pump is not a 30 minute operation. If it were my car, I would surely do it. Because this person has limited funds and no alternate transportation, I'm not sure he can take it to a shop to get it done right now, and thus the question about the temporary electric alternative.

I did see this: http://www.autoanything.com/brakes/69A3151A0A0.aspx

it's the SSBC vacuum pump for supercharged cars. but at $300, it still is probably better (and cheaper) to just do it the correct way and not worry about it for another 200k miles.

does anyone know of a kit for this pump? I see a lot of rebuild kits for another type of pump online, but not this one- am I missing something?

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1967 250SeC
1979 450sel 6.9 (usa)
2009 S550

In a recent thread on vacuum pumps (the one with Toronto in the subject line) someone mentioned that GM cars from ??? (late 80's? 90's?) had supplementary 12 volt vacuum pumps which might be capable of substituting for the mechanical version. They would be cheap from a junkyard.

It's not out of the question that 2 rebuild kits from an early style pump might fit the double diaphragm version since apart from having two diaphragms, they look similiar. If you could measure the diameter of the diaphragm portion of the pump on both style pumps, you might get a better indication of if that will work. I think the vacuum pump could be removed from the engine in about 30 minutes or less.

You may be able to replace the check valves without removing the pump. If my memory serves me correctly, they're under the rectangular cover held on with 2 screws. If you're not getting oil in the line that goes over to the intake, or in the main vacuum line,then I doubt a diaphragm has failed.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

that reminds me..

There is a clear line that goes to the air intake- that line has air coming out as opposed to vacuum. is that supposed to be the case?

maybe it is just a check-valve.. that would be nice.

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1967 250SeC
1979 450sel 6.9 (usa)
2009 S550

Yes, that's the vent line. If there's no oil in it or in the main vacuum line, the evidence points to a check valve.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13