RTH Needed! Vacuum Junction on top of valve cover: 83 300D - PeachParts Mercedes-Benz Forum

bnaquin · #1 06-29-2008, 10:24 AM

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?

pdrayton · #2 06-29-2008, 10:38 AM

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.

pdrayton · #3 06-29-2008, 10:40 AM

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

bnaquin · #4 06-29-2008, 11:02 AM

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.

bnaquin · #5 06-29-2008, 01:01 PM

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).

pdrayton · #6 06-29-2008, 03:00 PM

Ahhh, nice to have a simple repair that does so much...