Hey guys,

I've got an 81 300d with a 722.118 transmission. I think the connections are messed up on top of the valve cover. Note that it has 3 vacuum switches up there: 2 at the low throttle position & 1 at the high throttle. I've never seen a diagram that includes all 3, usually just 1 or 2.

Note that I'd rather not do the 'just disconnect a bunch of it & it'll be fine" approach. I've seen several diagrams that cover all the connections that are visible, but not for the connections from the 5-position to the actual vacuum switches.

Thanks in advance!
-tony

It would help if you post pictures of the current vacuum system routing.

Start with these two links.

It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...
http://www.peachparts.com/shopforum/showthread.php?t=158216

Transmission:
http://www.peachparts.com/shopforum/showthread.php?t=142395





Have a great day.

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Guys,

I've been off visiting my dad in the artic north.

OK, first question. Roy had said to see if the transmission modulator vacuum valve held a vacuum, & it didn't. I got a replacement (actually had ordered one a month or two ago out of suspicion). But the problem is that the original one has a metal rod & spring on it going into the transmission. The replacement does not. So the question is, is the new one defective, or is there a way to pull them out of the old valve & put them into the replacement.

OK, second question. Below is my vacuum diagram in text format. Again, this is a 81 300D with a 722.118 transmission. Are the lines connected correctly?

First, the 5 line connection on the housing on top of the valve cover looks like this:

X X
X X X

5 connections, I'll number as such (as viewed from the front of the car):

5 4
3 2 1

Note that on the inside of the housing is 6th pin, above pin 1 & to the right of pin 4, I'll call it pin 6. It is connected on the inside of the housing, I suspect it's just capped off but haven't checked. To the engine compartment here is how the lines are run:

1: top of modulator behind fuel injection pump through the green plastic restricter
2: side of modulator behind fuel injection pump, continues back through line that is open inside the passenger compartment
3: EGR valve
4: T's, one line goes to the transmission and other side goes to vacuum pump
5: vacuum pump

Now inside the housing there are 3 valves. Two stacked that are pressed just above idle and one on the left that is pressed when at very high throttle. I replaced all three of the little plastic part that goes between the rotating nylon part (moves when throttle pressed) and the metal pin inside the vacuum valve. Looking at them from the front & above, there is 1 connection on the left (pin A) & 2 on the left (pin B & C). Let me say pin B is further back (connected to pin A when at idle) and pin C is further front (connected to pin A when accelerating). So, a diagram would be (ignore the periods, they're there to make things space right):

(nylon rotating part)

. . . |-- B
A --|
. . . |-- C

(to front of engine compartment)

So, for connections:

left valve, top position
A: right valve pin B
B: connector position 4
C: open

left valve, bottom position
A: connector position 3
B: capped off
C: connector position 2

right valve:
A: connector position 1
B: top left valve pin A
C: connector position 6 (capped, open?)

Anyone have the same 3-vacuum switch setup on top of their valve cover? Otherwise, the vacuum system generally run around looks like the diagram at http://home.comcast.net/~phantoms/vacuum/egr_82_300d.jpg .

If I missed anything, please let me know & I'll add more details. Any help here on either question is really appreciated...

Thanks
-tony

This will get you started.

Modulator Replacement Help
http://www.peachparts.com/shopforum/showthread.php?p=2069428

Hey, many mucho thanks! The referenced summaries talk about adding a shim that applies to 722.3 -> 722.5 transmissions. I've got a 722.118, so I'm not sure that the shim applies to me.

But regardless, it looks like the metal pin & spring should just pull out from the old modulator, & insert into the new one. With that I should get things running again.

I will also be replacing the ATF dextron 3 fluid & tranny filter now. In the near/mid term timeframe I also plan to replace the K1 spring. If I still have the 2-3 flare left, then I'll look into doing this shim. I will come back here then for details regarding that.

So I think this answers my vac mod question unless I misunderstood something.

Let me put a bit more verbage behind my valve cover vacuum switch question. With it as connected today, here is what is connected at the 3 throttle positions:

Guys,

Good news first, the pin on the trans modulator valve came out. Took a bit of a tug a few times with the pliers, but it did come out. It didn't stick too well into the new valve, but it didn't easily fall out & with a little wiggling went back into the transmission. So progress there. Also drained just over 5 qts of tranny fluid & changed the tranny filter tonight, so tomorrow I'll refill & see if anything shifts! Adjustments will be fun.

Oh, one minor note. I had to remove the bracket for the muffler for easy access to the trans modulator valve. Not a big deal, but a note for anyone trying this.

OK, now for my new question. The 5 line vacuum connection to the 3-way vacuum switches on top of the valve covers. Mine has a 6th connection on the inside that is connected. Using my mityvac, I found that it actually goes to lines 3, 4 AND 5 of the connector (per my numbering system before)!!! I suspect this means that this little piece of plastic is broken. It's late, tomorrow I'll check the same plastic part on my other 300d & see if it is the same. Again, likely one more part of the puzzle. Would anyone please let me know what that 6th connector is really supposed to do?

Thanks again,
-tony

I got rid of all the crap.You need one vac line with a 3 way connector,from the a green dash pot,and rubber line to modulator on the injection pump.The bottom fitting vents to the air .From the other 3 way connector to black trans line.
So once again vac line to 3 way green dash pot to mod. on I.P. other end of 3 way to trans.
Bottom fitting on mod on I.P. goes to a vac line with no vac.

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Oldsinner111,

Let me repeat what you wrote to see if I understand how you routed yours.

You do not use any vacuum switches on top of the valve cover. Instead you have 1 vacuum line & only use the vac modulator by the injection pump.

You have it routed:

Vacuum line -> T (one side to green pot other side to tranmission)

other side of Green pot -> top of vac mod. by inj pump

side of vac mod -> open vent line in passenger compartment

Is that correct? So, let me describe how that will behave. At idle the vac mod is closed so the transmission is getting full vacuum. As I press the throttle, the vac mod slowly opens and decreases the vacuum. It will never get to zero due to the green dashpot, but it will lower the vacuum.

How about the EGR valve? Is it connected to anything?

I was looking at this picture: http://www.peterschmid.com/vacuum/1980/123_1.jpg . It is very similar. But it does tie the EGR to the tranny line, and it uses one vacuum switch on the valve cover to connect the EGR / tranny / vac to the top vacuum modulator by the inj pump via the green dashpot when above idle. Very similar bahavior, but does tie in the EGR.

Anyone else care to comment here? The help is really appreciated.
Thanks
-tony

Let me

No got rid of egr.Thoose little valves are a headache,rubber plug leaks,and the little connector to plug breaks.
Unless you are in California,then it has to look stock.

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

This is most likely your schematic:



You'll need to be a bit careful in randomly removing hoses from the connector because you do need the orifice in the transmission circuit.

Proceed as follows:

1) Remove the line between the connector and item 36 and toss it.

2) There is a T to the right of the #63 orifice. Remove the lower line of this T (goes to the five way connector) and toss it. Plug the opening in the T.

3) There is a T to the right of #65, the vacuum control valve. Remove the line from the T to the connector and toss it. Plug the opening in the t.

At this moment, you've got two remaining lines on the connector.

4) Pull those two lines off the connector and connect them with a short piece of hose.

Now, you're finished...........the transmission gets proper modulated vacuum..........and the EGR is disabled completely.

You can remove all the switches inside the black box..........the throttle pedal will have a smoother action.

Thanks Brian. OK, so you are confirming the same thing oldsinner111 said.

So to summarize:
1. open line to passenger compartment -> side of vac modulator.
2. top of vac mod. -> green dashpot -> tranny & vac line.
3. EGR unconnected.

So that will leave me with just a couple of adjustments:
1. Throttle link length to the vacuum modulator.
2. Vacuum modulator 'key' down at the transmission.

Put that way, adjusting it may be a piece of cake! Ah, but I'll hold my breath there until I get it done. #1 above will give me a way to reduce my vacuum going to the transmission at a given throttle. #2 above if screwed clockwise will give me a harder shift with more pressure and a later shift, counterclockwise will be a softer shift with less pressure and sooner shifting...

Changes are lined up for more experiments tonight. I'll need to reconnect the muffler bracket, put in about 5-6 qts of ATF, and redo the vacuum lines. Then it's out for a quick test to see if I can get past 1st gear, and finally into these 'adjustments'... I'm curious how much all this woudl have cost at a shop that knew what to do (or maybe I'm not wanting to know this!!! I've seen the $1-2k price that it would have been to rebuild my front end which was almost 10x the parts costs! (ball joint, UCA,tir rod, etc etc)).

Thanks again everyone, you've been great. I'm actually going to try to get to the Houston rally at the end of the month, if time permits & the wife doesn't get upset (as I've been in the garage with my metal 300d girlfriend a bit too much lately!).
-tony

If it's shifting too firmly, you're really not concerned if it reaches zero vacuum. That would just firm it up even more.

If you've increased the modulator pressure for no good reason, now would be a good time to return it to the original position.