On this date [February 22, 2008] I officially bestow this THREAD with the following secondary subject line title:
"The W123/W126 ' Tranny-Shifter Vacuum Control System ' "

Now back to my original POST below:
Samuel M. Ross
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So what am I talking about?… well let me see if I can make this POST a bit of a cliff-hanger with the really GOOD stuff at or near the end!

When I purchased a 1980 300D [na] to fix up for my 27 year-old starting-out banker Son, I wish I had known more about the automatic transmissions in these vintage MBZs. But I didn’t and so I took the car to my now independent MBZ mechanic friend and felt like I was doing the prudent thing.

Well as it turned out, and as I suspect is often the case, my now MBZ mechanic friend really did not really have a good grasp of the transmission vacuum shifting system on these cars. As I found out later, not only was/is he a bit too quick to blame poor shifting on “an internal transmission problem”, I also found out that he really did not have a good understanding of the “external” vacuum system that controls the shifting of these car’s automatic transmissions. In his defense however I now judge this to be the case with a lot of MBZ mechanics… even those who have relatively recent automatic transmission training as a MBZ dealer employee. IMHO too many just do not have a full appreciation of the intricacies of these old 721, 722, 723, etc trannies. Now that I think about it the recent MBZ grads probably receive even less training on these transmissions than my older friend did in the past… and more of their training is probably concentrated on the modern, computer controlled, transmissions that are still under warranty! Make sense?

In any event I gave up on my Son's car's 300K mile tranny and invested in a rebuilt from http://peterschmidtransmission.com here just south of San Francisco in Redwood City, CA… mainly because the dealer wanted ~$6K+ and I had read good things about Schmid's work and they have a 2-year warranty and usually insist that a warranty problem be brought back to them for adjustment under their warranty… even if it meant a long flat-bed truck tow at their expense. I later found that I used this warranty adjustment due to leak at the linkage output shaft on the side of the tranny !

I had the transmission ordered and swapped by the "experienced ex-MBZ dealer mechanic" who was starting up his new independent MBZ specialty repair shop. Well I think you will not be surprised to hear that it was evident that the newly rebuilt $2,000+ transmission job did not shift properly when returned to us and even the kickdown did not work at all. The young mechanic clearly did not have much training or experience with customer relations either. He acted insulted when I suggested some extra-curricular reading up on the subject of vacuum control systems was in order. I offered him a copy of the outstanding article by Steve Brotherton written in 2002 [ see http://www.continentalimports.com/ser_ic20242.html ] that this FORUM led me to. You know the article on how to set up the vacuum controls on these trannies! Well I guess I could have taught the young mechanic a lesson in a local small claims court where I feel quit comfortable presenting a case… but instead felt he might be more inclined to actually learn something if an old DIYer "break winder" like me tactfully adjusted what he obviously didn’t want or couldn’t adjust properly himself. So off I went gritting my teeth muttering “ I’ll teach this young wipper snapper ya ” !

A basic premise in Brotherton’s article had stuck in my mind... that you first need to concentrate on all the vacuum components that are external of the transmission [NOT including the modulator] and yes when I asked the mechanic to see his vacuum diagram, it turned out that he did not have the correct one and had hooked things up contrary to how they should have been. So the first thing I did was to obtain the correct diagram from http://peterschmidtransmission.com/.

This is where I have something NEW to relate to YOU, the regular readers of this FORUM… new and I THINK very significant addition to what Brotherton wrote in his article and so let me first repeat a portion of his article:

The vacuum source is a mechanical pump run off the injection timer. The "quantity" of vacuum is most important and is achieved by allowing flow of vacuum through a specifically sized orifice to the modulator. Control is done by leaks. A proportioned vacuum leak is attached in parallel. The leak is achieved by a valve attached to the injection pump (see Fig. 1 and Fig. 2) and regulated by a lever attached to the throttle linkage. The leak increases with throttle rotation.

I’m NOW talking about those 6 different nickel-N-dime “ RESTRICTED ORIFICES ” that I had a difficult time getting the p/n(s) for so that then my MBZ dealer's parts counter could order them for me... Sound familiar? Actually it was one of their mechanics who later passed on the p/n(s) to me in an e-mail. These orifices are shown on many of these car’s vacuum diagrams without telling you anything more… not even their size or color.

I started with the orifice shown for my 300D that was originally incorporated into the vacuum “T” on the main vacuum line that runs between the pump and the vacuum brake booster. There is very often one or two other orifices downstream of this and they effectively divide the system into multiple vacuum [pressure] zones… with the EGR usually the 1st zone, then what I shall call the shifting zone downstream [upstream if you think in terms of the actual flow of air in this "dynamic" system... yes, I think IF you stop and think of how air is moving inside the plumbing helps me a lot ! ].

It is in this 2nd zone that you find the different vacuum manipulating gadgets that “bleed”, switch and otherwise “tweak” the vacuum profile that is seen by the tranny’s vacuum modulator shifter.

I’m lucky for on my 1980 MBZ(s) these vacuum control systems are much simpler than say my father-in-law’s 1985 W126/617 300SD California delivered limo… and so I think cutting my teeth on the 1980 W123(s) as I have has made the learning curve easier! Of course if you are unlucky enough to own a newer model that is also a “California Car” then you could really be in deep “kimshy” for they are far more complicated.

Be patient now guys [and any gals IF any out there] for what I believe I have found is that understanding how to properly use these restricted orifices is KEY to getting the external vacuum components/system properly balanced and functioning. This external system together with the VCV must pass onto the modulator a variable vacuum that decreases from ~15 inches of mercury ["Hg"] vacuum down to or near “zero” as you drive and put the petal-to-the-metal! Yes, the main reason I am brow-beating you with this is that I want to REALLY emphasize that you MUST get this part right before you start adjusting the modulator… and my purchase of and having all six of the different colors/sizes of orifices was the best nickel-N-dime investment I made through all of this experience.

It appears that my “T” that branches off from the main pump-to-booster vacuum line had been replaced and no longer had its 1st stage of restricted orifice. So I ended up putting the smallest orifice in-line here and eventually was able to eliminate a 2nd orifice down stream of this for I found that this “California Car” runs like “poop” if you try to get the EGR to work properly… it just “ ain’t ” possible [ at least for me ] ! It causes the engine to loose power and put out black smoke when the pedal is down hard... the way these over-powered cars are driven by many of us!

So there, I’ve brow-beat you enough and will leave you be on this subject… that is unless you are foolish enough to come back for more of my verbiage!

Actually I should give out the p/n(s) and colors of these orifices again… and this time the sizes [I.D.] however these are questionable… so I recommend you use your “mark-one” eye ball looking through two or more at a time into at bright light to judge for yourself. My brown was smaller than the green but maybe it had been drilled out by someone as I already had it with the car:
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
Black.....0.6 mm.........____?_____
Orange..0.5 mm.........____?_____

I hope this helps someone out there… for that would make me feel like I have paid back a little for all the help this FORUM has been for me as I learn about my 3 MBZs! I'm out of here!!!!
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