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83' 300d
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Discussion Starter #1
So i definitely have a vac leak. I've tracked it down to the solid brown line that is attached to the 4 way connector that also provides vac to the locks and i think climate control. I've found a bunch of vac diagrams, but none say anything about this brown line.
I know that it somehow controls engine shut off b/c with it unplugged, the engine will not turn off with the key.

Where does this brown line lead to??? The vac leak is fairly fast, but not suuuper bad as if something isn't plugged in. Got any diagrams of where this solid brown line goes to?
 

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'86 W123 200, OM617 non-turbo, bastard 5-speed; '95 W202 C250 Diesel, OM605 non-turbo, 5-spd man
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Here

It's really straight-forward: it enters the cabin, along with the brown-blue tube, to the ignition switch. That's where things get tough - get a proper guide.

Refer to the FSM. It's available here somewhere. Google is your friend.
 

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83' 300d
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Discussion Starter #3
Before i try to troubleshoot this...

This brown tube that leads to vacuum switch on the ignition is supposed to hold vacuum, right??

So far, i put my fake MityVac on the brown tube by the brake booster and brought it up to like 20mmhg. It leaked down to nothing in like 10 sec. I take it that is NOT normal???
 

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'86 W123 200, OM617 non-turbo, bastard 5-speed; '95 W202 C250 Diesel, OM605 non-turbo, 5-spd man
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I admit 10 seconds sounds a bit extreme.

I have found some of the black connectors to be too big, thus allowing leaks. I've also had some vacuum tube a bit too small. But mostly, people forget that these tubes are brittle and cannot tolerate being bent around sharp corners; so most were just damaged by people working on the cars. Mechanics are especially rough, and then they'll easily tell you the vacuum pump (an expensive compnent) is shot, while actually it's just one of these tubes leaking from a brittle crack.
 

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1984 300D
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5,070 Posts
Before i try to troubleshoot this...

This brown tube that leads to vacuum switch on the ignition is supposed to hold vacuum, right??

So far, i put my fake MityVac on the brown tube by the brake booster and brought it up to like 20mmhg. It leaked down to nothing in like 10 sec. I take it that is NOT normal???
I cannot remember which brown line has the stripe but one goes from the Vacuu Shutoff Valve to the Steering Colum Vacuum Switch and the other goes from the Main Vacuum Supply to the Vacuum Switch on the Steering Colume.
So the 2 ends are under the Hood.

With the ignition switch off disconnect the Vacuum Line from the Shutoff Valve on the Fuel Injection Pump and plug that line and then apply vacuum with the a.k.a Mighty Vac.
If it leaks you have an issue with the Rubber Conector tubes, Plastic Tube or the Vacuum Valve itself.

If when you pulled the Vacuum Line off of the Fuel Injection Pump Vacuum Valve you had Engine Oil in the Line your Vacuum Shutoff is going bad. However, if it still shuts down the Engine you have some time to save for a new one.
 

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'86 W123 200, OM617 non-turbo, bastard 5-speed; '95 W202 C250 Diesel, OM605 non-turbo, 5-spd man
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4,275 Posts
I cannot remember which brown line has the stripe but one goes from the Vacuu Shutoff Valve to the Steering Colum Vacuum Switch and the other goes from the Main Vacuum Supply to the Vacuum Switch on the Steering Colume.
So the 2 ends are under the Hood.
Brown/blue is the line that feeds vacuum (what an oxymoronic concept, "feeding" by actually consuming...) to the ignition from the main vacuum on the booster and reservoir. Brown only shuts down the engine; it goes from the ignition switch to the IP.
 

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W-1-2-3 Go!
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If you have a leak in the brown line, it could be a bad shutoff valve, or bad ignition switch.

Plumb your handheld vacuum pump separately to the shutoff valve orifice and see if it holds vacuum independent of its attachment to the brown vacuum line. If it leaks, you've found your problem. If not, it may be the ignition switch.

If the shutoff valve tests okay, pull the other brown line connected to the 4-way connector but make sure you do NOT switch the two brown lines. Cap this line and test the other brown line (originally connected to the shutoff valve) for vacuum leaks. If you find a leak, then it's most likely the ignition switch. If not, your vacuum problem is elsewhere (beyond the capped line).

Reconnect both and test each system (climate control, central locking) the same way by isolating them from the main vacuum lines and testing if they hold vacuum.
 

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1981 Mercedes-Benz 300TD
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871 Posts
Cool, this solved my vacuum problem. Yes, DON'T reverse the lines or you WILL end up with a leak. Solid brown line from ignition to IP actuator and Brown w/ blue stripe from ignition to vacuum source.
 

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1981 Mercedes-Benz 300TD
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Thats weird... My car was the same way and I don't remember mixing them up but all I know is it leaked vacuum when I had it like yours and after swapping the lines I don't have a vacuum leak. Are your locks and HVAC vacuum pods connected to the system? I masked this problem for a while because I had minimal vacuum items connected in the first place.
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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My locks are out of the loop, but the HVAC and seat back lock systems are connected.

But hey, as long as it works.

In the first pic, you can see the solid brown line going toward the cabin.
 
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