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1973 450SL
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Discussion Starter #1
Does anyone knows what this part does? It goes on the vacuum line that goes to the rear of the car. I took it out to replace the fittings and clamps and it has a foam in the back that disintegrated completely when I pulled it out. I wanted to understand what it does in order to repair it. Also, aside from the fuel filler door lock, what else does this line feeds? I see two lines going to the back towards the trunk latch but I believe the latch in my car is mechanical. Thanks
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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31,892 Posts
I have been under a '73 countless times and don't remember seeing that. Trunk lock is part of the vacuum central locking system. It has a diaphragm.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Are you sure it's vacuum? Looks like fuel hose. Is there a part number on it? The return line is in that area. Expansion tank vent related?
 

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1984 380SL
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2,343 Posts
Are you sure it's vacuum? Looks like fuel hose. Is there a part number on it? The return line is in that area. Expansion tank vent related?
On my 380SL, the hoses in that area are connected to the evap system. There's a small L shaped diaphragm that allows pressure to escape the fuel tank when it jumps above a certain threshold.
Here's what I am talking about:


Is this a really early style fuel evap / charcoal canister system?
 

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1973 450SL
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Discussion Starter #6
Are you sure it's vacuum? Looks like fuel hose. Is there a part number on it? The return line is in that area. Expansion tank vent related?
It is. Someone connected a small fuel hose at some point to connect it to connect it to the main line. It is the vacuum hose that feeds the vacuum connections at the rear of the car.
 

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1973 450SL
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Discussion Starter #7
Ok, I was wrong, It is indeed a fuel tank vent valve, that functions to direct fuel vapors, in cars thru '73, to the crankcase for storage, and from '74 onwards to a charcoal canister. The use of that valve may have continued into the W123s.
In cars delivered into areas where evaporative controls were not used, the line from the tank terminated (at the point where the valve is) in a simple screened vent fitting.
 

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1973 450 SL
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That is part of your fuel evaporation control system (emissions on USA coded cars). Covered in this article from the 107 service manual. The foam can be replaced - I did it on a salvage part.
 

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1973 450SL
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Discussion Starter #9
That is part of your fuel evaporation control system (emissions on USA coded cars). Covered in this article from the 107 service manual. The foam can be replaced - I did it on a salvage part.
Thank you, this is very good information. I can see that the foam is used as a filter for the under-pressure condition and needs only to filter air being drawn into the gas tank. A simple air filter foam should do the job.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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I tried to find it in the EPC but when I ran the part number it came up with the one Beast posted.
 
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