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1984 500 SEC
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75 Posts
Discussion Starter #1
I am following the Vacuum diagram for my 500 SEC (with 500SL Engine) and I need to run a line to the Ignition Distributor to advance the timing. My distributor has 2 vacuum ports, both of which are currently connected to the vacuum system and are almost certainly going to the wrong places. Could someone please shed some light on whether I should be using the lower or upper vacuum port on the distributor as shown in my photo. And what is the difference between the 2 ports? I have done a lengthy search but cannot find any mention of this. Thanks

2640022
 

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84' 500 Sec gray market
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142 Posts
I felt the same way about my car, and discovered that my unit was shot. Have you tested it to ensure that it’s functioning properly? I’m not exactly sure about your version but I believe it should hold vacuum at one or both ports? Perhaps someone else can jump in to confirm that?
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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3,310 Posts
The vacuum line pointing up (obvious in the photo) is the vacuum advance, and is connected to the intake manifold. There may be some sort of control valve in the path, for emission control. The other one, pointing toward the distributor body is a retard line which is definitely for emission control, and should be modulated by a device somewhere.

To get it right, you're going to need to look up the vacuum line routing diagram for your specific car in the service manual.
 

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1984 500 SEC
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75 Posts
Discussion Starter #4
Thank you both for the replies.

I am following the vacuum diagram for my car and there is only one mention of the Ignition Distributor in the entire system. And that is the intake manifold (via a strainer valve) connects to the Ignition Distributor Advance.

I suspect the current connections by the PO are useless. The top port (advance) is connected to the Vacuum Switchover Valve by the throttle body. The lower port (retard) is connected to the lower chamber of the Warm Up Regulator. Doesn't make sense to me.

With this being the case, can I safely disregard the lower port on the distributor do you think?
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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3,310 Posts
If the engine came from an SL, maybe you should compare the routing from the SL with the SEC. You can't just unplug some of the lines and leave them hanging...
 

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Registered
1984 500 SEC
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75 Posts
Discussion Starter #6
That's a good point but the vacuum systems (within the engine compartment) are the same for both cars.

This is the 500 SEC system - it doesn't show the EGR part but it is the same as for the 500SL

2640059


And this is the 500 SL System:

2640060

Both just show the vacuum line connecting from the manifold - via the strainer - to the Ignition Distributor Advance.
 
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