84 300SD Main Vacuum Line Superceded - How To?

[Fuzzball]

So, the vacuum line that I have has been superceded by a new one that is nothing like what the old one is....

Here is what I have...note the connections for three vacuum lines in this general vicinity....One on the top of the white part (with a U shaped connector feeding the internals) then a 1 to 2 line connector on the back of the white check valve which is feeding the red with green stripe line and the brown line.....finally, a single line that feeds into the engine compartment seen right in the center of the picture.....




Then note the rest of the line here, with no vacuum connections anywhere:



And now, here is the new line that looks completely different from what I am using today:



I also had to order a new connector which is a three way connector.....and a vacuum line (which was not currently available, so I was going to fake it.....using some stock I have on hand), but there's nothing that tells me how to connect...



So.....

My question to the experts on the Shop is...has anyone done this swap and can you tell me what I need to do???

Thanks in advance!!!

[Fuzzball]

is there really nobody that has had to make this change? Nobody can help me out?

Bummer....

[toomany MBZ]

On my '83 SD the clear vac line is nearest the white check valve, {doubt it matters} goes to a "Y" connection, to the white thing on top of the IP, to a black line, I'm thinking auto trans, the other to cruise control. Can't figure how to send photos. You may be able to put a vac line off those two seperated leads on that hose. Mine, has like yours, the two just before the check valve. How did you determine the culprit is that line? Good luck, hope this helps.

[Brian Carlton]

Well, this is certainly a change. I cannot fathom why they would make such a change and which vehicle would benefit from it.

In any case, you need to supply vacuum to all the consumers that you previously had drawing on the main vacuum line.

The only question is whether the consumer has a restriction on the main line.........or not. My guess is that none of the supply line ports have restrictions with the exception of the line coming from the white valve. You'll need to verify this on the old line.

If there is no restriction, you can use any port for the vacuum. If you wish, you can get a Y or a T connector and use one port to supply two consumers.

If you don't wish to utilize any of the new ports closer to the front of the engine, then just get a rubber cap for them.

The design of this new line makes no sense as all the consumers (EGR, VCV, ignition, and climate control) all meet near the fusebox.

[Fuzzball]

Originally Posted by toomany MBZ

On my '83 SD the clear vac line is nearest the white check valve, {doubt it matters} goes to a "Y" connection, to the white thing on top of the IP, to a black line, I'm thinking auto trans, the other to cruise control. Can't figure how to send photos. You may be able to put a vac line off those two seperated leads on that hose. Mine, has like yours, the two just before the check valve. How did you determine the culprit is that line? Good luck, hope this helps.

Thanks for the suggestions......

I used my Mityvac off the Y tube (with the opposite side of the Y plugged with a golf tee) with the car running and the vacuum would bounce around from zero to 15 and back to zero....figure that has to be a problem....

When I checked the vacuum off the tube itself, it was fine...and I could pump up the vacuum into the brakes after a LOT of work....that single check valve was the only place I had a problem.

[Fuzzball]

Originally Posted by Brian Carlton

Well, this is certainly a change. I cannot fathom why they would make such a change and which vehicle would benefit from it.

In any case, you need to supply vacuum to all the consumers that you previously had drawing on the main vacuum line.

The only question is whether the consumer has a restriction on the main line.........or not. My guess is that none of the supply line ports have restrictions with the exception of the line coming from the white valve. You'll need to verify this on the old line.

If there is no restriction, you can use any port for the vacuum. If you wish, you can get a Y or a T connector and use one port to supply two consumers.

If you don't wish to utilize any of the new ports closer to the front of the engine, then just get a rubber cap for them.

The design of this new line makes no sense as all the consumers (EGR, VCV, ignition, and climate control) all meet near the fusebox.

Thanks Brian...I'll have to do a little more investigation....hmmm....

You are right, this design makes absolutely no sense...they did require a special three way connector and more vacuum line...but no explanation of how to put it all together.

I've gone through every 300SD picture I can find on Ebay (Closed and active) looking for ANYONE that has this new hose.....but nothing...

I'll figure it out sooner or later......in the meantime I'll just have to make sure I keep up the RPM's in bumper to bumper traffic for my brakes...if I have to drive the car at all.