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  #1  
Old 06-29-2008, 10:24 AM
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Join Date: Dec 2005
Location: San Antonio, Texas
Posts: 81
RTH Needed! Vacuum Junction on top of valve cover: 83 300D

I'm finding myself in a bind this morning and could really use some help. A few days ago I traced some vacuum leaks back to the vacuum junction (cruiser control switches?) on top the valve cover (under the black plastic cover) of my '83 300D. The plastic junction that connects the lines together was incredibly brittle and several of the connection points were broken. I purchased the correct parts and while reinstalling noticed the connection points looked like they were in the wrong position to begin with. They may have been up-side-down or backwards. After examining the new parts I'm pretty sure this is the case. However, I don't know the correct position to connect everything.

Has anyone dealt with this issue before?
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RTH Needed! Vacuum Junction on top of valve cover: 83 300D-img_0011.jpg   RTH Needed! Vacuum Junction on top of valve cover: 83 300D-img_0009.jpg   RTH Needed! Vacuum Junction on top of valve cover: 83 300D-img_0010.jpg  
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1983 300D
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  #2  
Old 06-29-2008, 10:38 AM
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Join Date: May 2005
Location: Fernandina Beach, Florida
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Have a look at the fsm at

www.pauldrayton.com/uploadfiles/merc

There are some vacuum diagrams in there somewhere.

However, the 2 switches on there are not essential. The top one engages the EGR (not essential) at full throttle.

The lower switch makes the downshift of the tranny smoother when the gas is off, and you're coasting.

I've removed the EGR vacuum switch from my 83 240D. The lower tranny switch is put in serial with the vacuum source going to the vacuum control valve on the IP. At idle it shuts off the vacuum to the tranny, so it doesnt downshift. When the throttle is engaged it switches on and gives vacuum to the tranny. So that's all you have to connect up. Make sense?

There are probably full vacuum diagrams on the sticky at the top of the forum. Have a search.
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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles
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  #3  
Old 06-29-2008, 10:40 AM
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Join Date: May 2005
Location: Fernandina Beach, Florida
Posts: 626
Heres the vacuum diagram from Vacuum Diagrams

The two switches are the same as yours, just set side to side, not on top of each other. The one on the right in the pic is the tranny switch

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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles
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  #4  
Old 06-29-2008, 11:02 AM
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Join Date: Dec 2005
Location: San Antonio, Texas
Posts: 81
Perfect. Thanks for the help. I was surprised to see all but one of the connectors was broken and sitting in such a way that they looked connected unless you physically touched them. This may also take care of the transmission downshift upon deceleration that I've noticed from time to time.
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1983 300D
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  #5  
Old 06-29-2008, 01:01 PM
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Join Date: Dec 2005
Location: San Antonio, Texas
Posts: 81
WOW! Not only does my engine actually shut off every time I turn the key off, all my door locks work correctly and my transmission shifts much better! Thanks for all the help people. No more vacuum leaks (that I've found).
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1983 300D
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  #6  
Old 06-29-2008, 03:00 PM
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Join Date: May 2005
Location: Fernandina Beach, Florida
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Ahhh, nice to have a simple repair that does so much...
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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles
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