I looked at the diagram at: http://peterschmid.com/vacuum/1977_1985/617_95/1981_1984.jpg
and I think this might be the vacuum diagram for your 81 300SD... but I'm not sure. IF this is the correct diagram for your car, I agree with Brian that the vacuum switching device on top of the valve cover only controls when the EGR is sent vacuum!

What engine does your 1981 300SD have?

Sam

All W126 diesels from '81-'85 have the 617.

All W126 diesels from '86-87 and '90-'91 have the 603.

Brian - Yes I knew that any "300" model has 5 cylinders and that means it will be a 617 engine, but in order for me to track down and sort through the 30+ vacuum diagrams on the PeterSchmid.Com website, I need to know if it is a:
617.91 which uses the diagram at: http://peterschmid.com/vacuum/1977_1985/616_617_91/616_617_91.jpg OR a,
617.95 which means it might be the diagram at: http://peterschmid.com/vacuum/1977_1985/617_95/1981_1984.jpg
I don't have the ability to make quality printouts of these and the one you have from the FORUM to study so I am forced to leave this up to 300SD81 and you Brian. Maybe this exercise will prove needless... it's just that I have this thing about trying to make sure I have the proper diagram to start with... and I know these SD(s) up through 1985 do begin to get complicated!

Let me look at these two I just referenced... hmmm... I'll go blind trying to read these two on the monitor I have here now. I can tell they are different and my fuzzy memory tells me it should be a 617.95 engine and the diagram for this appears less complicated but that's all I can tell.

Sorry if all I did was to muddy the water,
Sam

I think I have the 617.95, since I only had 3 lines going to the black box, and no electric valve anywhere between the box and the EGR.

Well, I found a way to get some clarity to those vacuum diagrams… and I hope you are right about the engine being a 716.95 for that diagram is certainly less complicated with there being only 3 vacuum lines off the “Switchover Valve” –vs- the 5 lines coming off in the other 617.91 engine diagram. I think Brian is probably correct about the Switchover Valve on your car NOT being designed to directly effect the tranny shifting unless it was the source of leak(s)… but my one lingering concern comes from my NOT understanding what the function of the middle vacuum line is… this is the one that is shown just below the #71 in the 617.95 diagram… and it goes down, over to, and eventually connects via a 3-way connector to the vent line of the VCV on the injection pump. This arrangement with this connecting as it does to the VCV vent line is a marked departure from my two 123 chassis vehicles from only 1 year prior. The only thing I see that the Switchover valve could be doing with this line is for some reason porting vacuum to the vent side of the VCV under certain throttle positions… and this [I’m speculating here now] would slow down the bleeding effect of the VCV. So IF I’m correct, this would directly effect the way the tranny shifts when the throttle was in a certain position or a range of positions.

But I cannot be sure of the above. I have an 1985 300SD back at home that I might be able to further resolve what this vacuum line & connection are intended to do… but that will have to wait until I return to California!
Sorry I cannot help further now. If you are looking to optimize your car's shifting, eventually you will need to "dynamically" monitor the vacuum being sent to the tranny's vacuum modulator.

Do you have a vacuum test pump & gauge? This might seem complicated, but thank God you don't have a 1985 CA 300SD with the mirrad of "stuff" on this same system... see: http://peterschmid.com/vacuum/1977_1985/617_95/1985_cal.jpg

Best regards,

Sam

All W126 from '77-'85 use the 617.95 engine.

My 1984 300sd is slipping on the shifts from 3 to 4. I measured the pressure at the VCV and get 14 at idle and 5 at full throttle. I have tried a normal transmission flush and I have TransX in right now and will flush again this week.

I have disconnected the vacuum from the VCV to the transmission modulator and the shifts a "rugged".

It appears that the box on top of the valve cover was removed before I bought the car.

I am wondering if the test I performed was valid since I did this in the driveway in Park. Does it matter that I am not gear and driving down the road?

__________________
1984 300SD 148K Gold
1979 300SD 142K Cream
2001 Audi TT Roadster 60K
2005 Chevrolet 3500 13K

That's fixable.

The VCV has a small round dome cover on the side that faces you when you look at it. Carefully pry off this dome (need a tiny screwdriver or knife).

Under the dome is a small slotted screw.

Remove the hose from the top of the VCV and connect up the Mityvac. Pump up the Mityvac to the 14" reading that you got before. It should hold there.

Now, very carefully, turn the slotted screw clockwise about 5 degrees and watch the Mityvac gauge. It will start to drop in a hurry. When the gauge gets down to 8".........stop.

Remove the Mityvac, reconnect the hose to the transmission modulator, put the plastic domed cover back on, and take it for a test drive.

Problem solved.

“PatMan” – Especially because you are a resident of California as I am, I would ask you to determine which car you have… a 1984 “Federal” or a 1984 “California” car. When it comes to the Engine/Tranny Vacuum control systems there is a very significant difference:
The “Federal” car’s diagram can be seen at:
http://www.peterschmid.com/vacuum/1977_1985/617_95/1981_1984.jpg AND
The “California car’s diagram can be seen at:
http://www.peterschmid.com/vacuum/1977_1985/617_95/1984_1985.jpg
It's a good chance that you have a “California” version and if so this could lead you to believe that someone had removed the mechanical Switchover Valve [#64a/64b] from the valve cover… because the California version car does not have a mechanical Switchover Valve. A study of these two diagrams quickly shows that.

Can you take these two diagrams [from the WebSite of a tranny rebuilder here in the S.F. Bay Area]… take these and determine which car you have. I’m sorry but my limited experience with the 83-85 models of these vintage diesel MBZ(s) forces me to work first from information on the diagrams… plus I have this need to know with more certainty which car I’m advising you on before I give any advice.

Q – Have you read this article which [IF NOT] I know you will agree is germane to this subject? http://www.continentalimports.com/ser_ic60442.html
Regards,

Thanks Brian and Sam. I am honored to have your guidance. As soon as I pry the car away from my daughter, I'll check it out. I have tried to determine if I have a Cali or Federal car. From my initial investigation it appears that the car was first sold in California. I looked over the Cali and Federal diagrams, but without the car, I can't confirm. Thanks so such for pointing this out.

Sam, just as you figured, the "stuff" on the top of the valve cover has previously been removed. I noticed the 3 holes on the top of the valve cover and it was obvious that something was screwed in at one time (shiny metal). After my reading of several threads, I believe someone did the "get rid of that box and bypass the EGR" thing some time back.

I will follow Brian's suggestion and follow the adjustment routine. I have the Mityvac and am prepared to get my nitrate gloves dirty.

I have read the Steve Brotherton article and a couple of other useful threads related to "vaccum tuning" the transmission. I've done the flush. I'm on the Trans-X and will reflush and change the filter this week. Now its time for a little "adjustment". I love it. I will read the article that Sam suggested.

I can't say enough about all the great advice both of you have given and the appreciation I have for you willingness to share you knowledge. Thank you.

Patman

__________________
1984 300SD 148K Gold
1979 300SD 142K Cream
2001 Audi TT Roadster 60K
2005 Chevrolet 3500 13K

and IF you do have the '84 "Federal" car rather than the "California" model, count your blessings!!! In either event, don't forget that those restricted orifices are "critical" to helping to establish the proper balance between the multiple vacuum [ aka "lower pressure"] zones so that the VCV can properly bleed off the vacuum and accurately simulate throttle position in these Engine/Tranny control systems.
Regards,

Thanks for reminding me. I went out yesterday to get some vaccuum line, "T's" and the orifices to make a test tool. I could not find the line and orifices at your normal auto parts stores in this area. Could you give me some hints on where I can find this stuff?

__________________
1984 300SD 148K Gold
1979 300SD 142K Cream
2001 Audi TT Roadster 60K
2005 Chevrolet 3500 13K

Managed to do some checking on my '87 300D Turbo today.

At hot idle, got the following -

Small connection on vacuum pump itself - 22"

At 3 way connector to vacuum amplifier and vacuum reservoir - 15"

Line from vacuum amplifier to tranny, measured after green damper - 9"

Line from green damper on vacuum control valve to amplifier - 1"

Does this sound like it's anywhere in the ballpark for normal readings?

__________________
Just say "NO" to Ethanol - Drive Diesel

Mitchell Oates
Mooresville, NC
'87 300D 212K miles
'87 300D 151K miles - R.I.P. 12/08
'05 Jeep Liberty CRD 67K miles
Grumpy Old Diesel Owners Club

... and in this instance I did a SEARCH on this WebSite/Forum for "orifices p/n" and came up with hits on two of my old POSTS that give us this on the orifices:
Color-----I.D.-----------P/N:
Yellow……2.0 mm..……..1162760929
Red……….1.1 mm….…….1162761029
Blue………1.0 mm…………1162761129
Brown……0.9mm….……..1162761429
White……0.8 mm…………1162761229
Green……0.7 mm…………1162761329
I think there are 1 or two other colors... black. I see that the sponsor of this WebSite has the yellow one for $1.67 at: http://catalog.peachparts.com/item.wws?sku=1162760929 ... but I come up empty when I try the other p/n(s) in this series. I think you will most likely need the smaller ones in this series of p/n(s) so IF YOU DO NOT find these resonably priced through your local MBZ dealer's parts department Contact "Phil" at our sponsor "FastLane" at: www.Phillip@MercedesShop.Com or by Telephone at 888-333-4642

IF you have NOT purchased a "Mity Vac" pump/gauge [~$20 to $60], you can purchase one in a KIT which often has a whole selection of adapters, caps etc that can be invaluable in vacuum sleuthing. Select a hand pump that is metal [not plastic]. Check out this ad at:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92474
Regards,

Brian, you da man!!!

I did just as you explained and it's shifting without flaring in any gear.

There was either confusion on my part or a slightly different configuration on the VCV. Once I pulled the cap off, there was a bolt with a nut. I was expecting to see an adjustment screw. I had read some posts that indicated that these VCVs were different including some the had no way to adjust. The bolt just seemed to be connecting a lever that is related to the accelerator. I thought it was just holding things together. I first "tightened" the nut and took some measurements. The vacuum was at 16 (vs. 14) and there was no reduction at throttle. I then "loosened" the nut and adjusted until I could achieve "0" at full throttle instead of just setting at 8. I ended up at about 10 at idle and 0 at full throttle.

After reconnecting everyting, the test drive proved it was working just fine.

I agree with Sam's initial assessment at the beginning of the thread. Now it might be time to make adjustments to the modulator and/or the throttle adjustment (I forgot what the official name is), after getting the VCV in order. I think I will take my daughter out for a ride and see how she drives the car before making adjustments. I could probably soften up the modulator a little, because I firmed it up last week in desparation.

BTW, Sam, it is the dreaded California configuration.

Thanks again Brian and Sam for you guidance and wisdom

__________________
1984 300SD 148K Gold
1979 300SD 142K Cream
2001 Audi TT Roadster 60K
2005 Chevrolet 3500 13K