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#1
03-05-2012, 02:01 PM
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Vacuum Leakage
I think that my main supply line might be leaking where it connects to the brake booster.
Also there's a noise coming from the vacuum pump. I installed a different used check valve in case that was the problem. They are audible when pumping vacuum into the system from the brake booster. Here is a video of both: vacuum.MOV - YouTube It's an 82 300sd 
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#2
03-05-2012, 02:29 PM
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Perhaps try spraying some mineral oil where you might suspect it is leaking? If the oil is sucked in, you know where your leak is.
We would do this to locate intake leaks, but using propane, or other combustables. When the idle was effected, we knew we were close. Note for others reading this: Clearly this vac leak is not to the intake manifold, but the closed vac system, so in this case there would never be any effect to idle. My reference above is typcal to gas powered motors. No mention in OP, did you try tightening the connections? I am currently working through some vac issues. It effects all systems on these cars. Best of luck.
__________________
83 300TD (need rear wiper assembly dead or alive) 84 300SD Daily driver 85 300TD almost 400k miles and driven daily. 98 E300D *sold 86 300SDL *sold and made flawless 10 hour journey to new home. 
Last edited by Renntag; 03-05-2012 at 02:31 PM. Reason: clarification.
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#3
03-05-2012, 02:33 PM
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I tried tightening the connections, yes. I have swapped the brake booster thinking that was the problem.
The high-pitched squeaking noise from the connection at the booster is the same noise as when I loosen the connection, which make me think it is definitely the supply line. I tried using soapy water and didn't see any bubbles. Don't have mineral oil on hand... The noise by the vacuum pump is dumbfounding me completely, unless it's two bad check valves.
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#4
03-06-2012, 03:30 PM
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Blew into the connection by the booster and was able to get the same squeaking noise, isolating it to the white plastic connector that the larger vac line comes off of.
I put some RTV sealant around the area between the end caps and the main body and the squeaking went away. I think it's still leaking a little bit, but some of the vacuum-related problems improved a little bit. So, I definitely want to find a good used main source line. Cheapest new one I can find is $74. And need to figure out what this noise by the pump is...
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