Since the health of the vacuum system is so important for reliable operation of my '84 300SD that I just bought, I started thinking about going through vac lines and upgrading the rubber ones to silicone ones. I've also seen a few Y-fittings under the hood, and I was thinking about upgrading those to Nylon or stainless steel Y-fittings to make sure they have a long life.

Are there any reasons against using silicone vacuum lines in these diesel cars? What is the standard size for vac lines used in these cars?

I don't know about silicone lines but here's a good reason not to randomly replace fittings:

http://www.peachparts.com/shopforum/showthread.php?t=143848&highlight=glorious

Danny

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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That's a good point and a great thread - thanks for the link!

Certainly I wouldn't replace a vac fitting on my car with the one that's different in structure from the OE one - only if it's a plain ol' fitting without the special "orifice" bit or without other special custom sizing concerns that could affect air flow rates within the vacuum system.

I replaced all my rubber vacuum lines with silicone hose I had. The rubber lines were all brittle. I have a 85 so my transmission vacuum line is feed through the vacuum modulator.

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85 300D Turbo

Why? The rubber connnections are good for about 20 years and are really cheap to replace and work great. Unless you just like to spend lots of time on something that will not give you a payback, then just replace the connectors with new ones.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

Maybe you're talking about something different than the silicone tubing I use for fuel line... but I think it would make terrible vacuum line and connectors. Very easily torn, hard to use with clamps... blah. The only reason I use it for fuel lines is to see if I get air in my veggie lines.

Bill

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'87 300SDL, intensely modified Greasecar setup, with nickle plated heat exchanger, 3 valve setup, 312,000 miles
'95 Suburban diesel, Greasecar basics, 16 plate heat exchanger, mercedes fuel lines, Racor filter
'85 Renault Alliance converted full electric vehicle

I am not sure if silicone is the best choice for vacuum lines on Mercedes diesels (im just starting to learn about them), but on usual gasoline-engine cars that I'm used to, silicone is pretty much the best choice out there for vac lines. It stays tight, flexible, doesn't crack like rubber, and can gracefully withstand temperature extremes. I think silicone vac lines are pretty much forever, unless they are exposed to petroleum fumes or oil, which would degrade them eventually.

Perhaps MB uses superior rubber formulation in their vac lines and connectors. But rubber is rubber - it does toughen over time if exposed to the elements and becomes less flexible, which leads to loosening at vac line joints and causes leaks.