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Old 07-10-2006, 11:18 PM
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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
========================================================
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!!!!
===========================================================================================


Last edited by whunter; 09-20-2012 at 03:59 PM. Reason: repaired dead link
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  #2  
Old 07-11-2006, 01:48 AM
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do these orifices have a direction? Like is one opening bigger than the other? Or is it just a straight even opening? If I wanted to test my system, you're saying I should have a vacuum of 15 or so to the tranny at idle and that should decrease to 0 as I move the throttle open? What do the different orifices control specifically? The level of vacuum at idle or the rate at which it transitions to 0 at higher rpm or both? I would guess that the orifice controls the vac level at idle and the tranny vacuum valve on the IP controls how it changes relative to RPM. Is that right?

When I checked my system a while ago I was confused since I was getting a full 22 to the tranny and to the top of the valve on the ip, but i was getting 15 to the EGR. This was at idle. I don't have any shift problems that I know of, though, so I didn't worry about it. But it seems like that is backwards. That is why I ask if there is a direction to the orifice. My orifice is blue by the way (and please don't misconstrue that! ).

Do you know what the green dashpot does exactly? I have heard people say they give a controled leak.

Thanks for the info you posted.
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1984 300d 223k
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Old 07-11-2006, 03:17 AM
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Jackson... before I can begin to speculate anything...

about your specific vacuum setup, I would need to see the diagram specific for your vehcile.

Go to this WebPage:http://PeterSchmidTransmission.Com[url]
From this point you need to know specifically which engine you have... either 617.91x series or 617.95x series. Which engine you have determines which of three diagrams we should reference for your car.

If you can sort your way through this maze of more than 30 vacuum diagrams on www.PeterSchmidTransmissions.Com and find YOUR car's diagram here is how to give me the precise WebPage address for any of these diagrams. You initially click on the diagram to make it large and readable.
Then you right click on the enlarged diagram and select "Properties" from the pop-down menu option.
This will give you the detailed and often lengthy html address.
For example: http://PeterSchmidTransmission.Com/vacuum/1977_1985/616_617_91/616_617_91.jpg

Start at: http://PeterSchmidTransmission.com , then click on Vacuum Schematics, etc. and try to locate the diagram... then obtain the full http address as described above and POST it here or send it to me via the Forum's E-mail, then I might make some sense of your questions. If you have a vacuum component none of my brood of cars has, then I might not be able to do more than just speculate. But give it a try. You are lucky, you say you know of no problems with your car's transmission... but maybe we can help you gain a better understanding of your system so you will be better equipped to deal with any future problems!

I never said this would be simple... but it's a lot easier one I know the proper vacuum diagram/schematic is for your car!

Note that there also 7 pages of instructions on how to test the key " Vacuum Control Valve " which costs ~$200 if it is no longer able to vary the final vacuum properly.

Sam

Last edited by Samuel M. Ross; 03-17-2009 at 02:25 AM.
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  #4  
Old 07-11-2006, 07:29 AM
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Good poop , Sam. I struggled with my 300D transmission early on until I concentrated on getting the proper vacuum at the Vacuum control valve outlet per the Brotherton article. Since I had blocked off my EGR, I bypassed and elimnated my switchover valves on top of the valve cover- that may be a path for those of you not concerned with EGRs and emissions testing.

Rick
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Old 07-11-2006, 10:02 AM
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Thanks for the part numbers and the low down.

My 83 300td shifted really nasty, flared, slipped and was sloppy to boot. Due to all the reading on this forum, I "fixed it" for about 30 cents worth of vaccum hose and a couple of BB's....yepper good vacuum is everything.

Put an offer in on another 300td and the lady called me back and I went to look at the car. She had told me it was low on power and did not shift good. I took some vac hose, and bb's with me. Cleaned the plugged banjo bolt, blocked off the EGR vac hoses, replaced the vac to tranny connection....totally different car.

I advise checking ALL vacuum connections as THE starting point on these older cars....it can make a world of difference!
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  #6  
Old 07-11-2006, 10:20 AM
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My 300SD always slammed into gear, and I always suspected that there was an internal problem too, especially considering it has over 300k miles. Anyway, I drove it like that for several months, then one day I was trying to get the center vent to work, and realized that the pod was shot. Not wanting to bother with the pod, I took it apart so it was always open, and plugged up the tube. After driving it I was shocked that it now shifted like butter, and the shift points were right where they are supposed to be! With as many Benz's with bad pods out there, I would say that be the first place a person should look when they have a rough shifting tranny.
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Old 07-11-2006, 11:08 AM
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Quote:
Originally Posted by Jmana
My 300SD always slammed into gear, and I always suspected that there was an internal problem too, especially considering it has over 300k miles. Anyway, I drove it like that for several months, then one day I was trying to get the center vent to work, and realized that the pod was shot. Not wanting to bother with the pod, I took it apart so it was always open, and plugged up the tube. After driving it I was shocked that it now shifted like butter, and the shift points were right where they are supposed to be! With as many Benz's with bad pods out there, I would say that be the first place a person should look when they have a rough shifting tranny.
Jmana - how did you plug that line? Did you do it at the point where the vac line runs from behind the CCU to the center vents?

I'm having this same exact problem you had. The leak is definitely in the climate control system and the center vents are a good bet, though I'm not positive yet. Ever since I figured out where the leak is I've been turning defrost on right before I shift because this makes it smooth.

Quote:
Originally Posted by Samuel M. Ross
...Be patient now guys [and any gals out there] for what I believe I have found is that understanding how to properly use these restricted orifices is absolutely KEY to getting the external vacuum components/system properly balanced and functioning. This external system must pass onto the modulator a variable vacuum that decreases from ~15 inches of vacuum down to or near “zero” as you drive and put the petal-to-the-metal! Yes, the mail 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....

Sam
I noticed on my car, which is a CA car, the vac going to the tranny is 20.5" hg when it seems to be working correctly. I'm not sure if this is the 'proper' number or not, but I suspect the CA models with the blue transducer are different in this respect. As you mentioned, we CA owners have some unique aspects of our cars to puzzle over.

Another great write-up, Sam!
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Old 07-11-2006, 11:48 AM
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Quote:
Originally Posted by miner
do these orifices have a direction? Like is one opening bigger than the other? Or is it just a straight even opening? If I wanted to test my system, you're saying I should have a vacuum of 15 or so to the tranny at idle and that should decrease to 0 as I move the throttle open? What do the different orifices control specifically? The level of vacuum at idle or the rate at which it transitions to 0 at higher rpm or both? I would guess that the orifice controls the vac level at idle and the tranny vacuum valve on the IP controls how it changes relative to RPM. Is that right?

When I checked my system a while ago I was confused since I was getting a full 22 to the tranny and to the top of the valve on the ip, but i was getting 15 to the EGR. This was at idle. I don't have any shift problems that I know of, though, so I didn't worry about it. But it seems like that is backwards. That is why I ask if there is a direction to the orifice. My orifice is blue by the way (and please don't misconstrue that! ).

Do you know what the green dashpot does exactly? I have heard people say they give a controled leak.

Thanks for the info you posted.

The orifices have no direction. They are simply a narrow plastic tube with a specified inner diameter.

You vacuum at idle should be less than 15". Somewhere around 10" would be preferred. I've got the SD set at 8" and the shifts are crisp but don't bang.

The orifices control the flow rate. Under a steady state condition, they have no effect. But, since the VCV works via a bleed, the orifice serves to control the amount of flow to allow the VCV to attain 0" vacuum. Without the orifice, the VCV could not leak sufficient air to reduce vacuum to an appropriate level.

The green dashpot is also similar to an orifice. It dampens the changes in vaccuum level to the VCV.

Get rid of all the lines to and from the black box on the valve cover. Two of them go into separate "T's" on the driver's side of the engine. Just take out the T's and connect the remaining ends with a section of vacuum hose. Many times, the source of poor shifting is due to excessive leaks via the 3/2 valves inside the black box.
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Old 07-11-2006, 12:29 PM
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Thanks Brian, I see you beat me to answering a question POSTED earlier...

but here is a photo of the 5 orifices I'm not using... and you know what they say... " let Sam post photos and much less verbiage!" At least I hope my photo is attached after all the trouble I had getting it down to less than 65K size!

Brian - I have learned to agree with your observations and advice... but let me supplement a little where you have said:

"You[r] vacuum at idle should be less than 15". Somewhere around 10" would be preferred. I've got the SD set at 8" and the shifts are crisp but don't bang."

When I say ~15 in of vacuum, I'm talking about what it starts out at just before you first depress the accelerator and the vacuum switch on top of the valve cover brings the IP's Vacuum Control Valve [VCV] into the circuit and begins to bleed off the vacuum levels. On my car this initial drop in vacuum is to ~10 in just as you indicate. So we are talking the same number once this clarification is made. Some day FORUMs like this will allow me to attach a short digital video clip of my vacuum gage readings and an accompanying audio track explaining what's what.

IMHO, the main thing here is that when you start testing the the car with the vacuum gage held securely under your windshield, you want to see the reading approach "zero" just as the accelerator reaches the floor. If the vacuum is not dropping low enough, you have two options: (1) to try and adjust the VCV and get it to "dump" or bleed more of the vacuum off, or (2) to further restrict the vacuum at or near its source. I find the latter more appealing... but we should always be ready to try (1) as well.

Again, the game plan is to get the vacuum being seen at the connection going to the tranny's vacuum control modulator to vary from ~15-10 down to zero as the car is driven and the accelerator is pressed.

Enough for this clarification! I hope my photo is there when I submit this... right NOW!
Sam

Last edited by Samuel M. Ross; 03-17-2009 at 02:25 AM.
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  #10  
Old 07-11-2006, 12:30 PM
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I feel a little stupid. I really want to do this. My 300td shifts like junk. Kinda sloppy all over, and really hard 1-2. What kind of gauge do I use to measure the vacuum?? Where do I connect it to test the 15" reading? What purpose do the bb's serve?

I know, I feel stupid.

Thanks,
Chris
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  #11  
Old 07-11-2006, 12:34 PM
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Quote:
Originally Posted by Samuel M. Ross


When I say ~15 in of vacuum, I'm talking about what it starts out at just before you first depress the accelerator and the vacuum switch on top of the valve cover brings the IP's Vacuum Control Valve [VCV] into the circuit and begins to bleed off the vacuum levels. On my car this initial drop in vacuum is to ~10 in just as you indicate. So we are talking the same number once this clarification is made. Some day FORUMs like this will allow me to attach a short digital video clip of my vacuum gage readings and an accompanying audio track explaining what's what.
When I say 10" of vacuum, I'm talking about the setting at idle, simply using a Mityvac into the port. When you first depress the accelerator, the vacuum will start at 10" and begin to drop from there.

15" is too much vacuum, IMHO, and the transmission will shift fairly softly.......somewhat mushy.........under most driving conditions.

As I mentioned, the SD is currently set at 8" at idle.
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Old 07-11-2006, 01:30 PM
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Quote:
Originally Posted by Maroon 300D
"Jmana - how did you plug that line? Did you do it at the point where the vac line runs from behind the CCU to the center vents?
I'm having this same exact problem you had. The leak is definitely in the climate control system and the center vents are a good bet, though I'm not positive yet. Ever since I figured out where the leak is I've been turning defrost on right before I shift because this makes it smooth."


I just plugged the line going into the pink pod. I also pulled off the cap, and extended the rod fully, so now I have full time air out the centers (which I can control with the slider)
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Last edited by Brian Carlton; 07-11-2006 at 01:47 PM.
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Old 07-11-2006, 02:05 PM
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Brian... to solve my photo POSTing problem...

I deleted some of my past larger attachements !

Back to something you POSTed earlier... where you said:

"Get rid of all the lines to and from the black box on the valve cover."

Do you mean this literally?... if you are you speaking of what is often called the 3-in-1 vacuum valve? Well on both my 240D and 300D MBZs I have concluded this vacuum valve not only switches the EGR on/off but also turns on/off the "bleed" effect of the VCV on the IP. I'm not certain but I think this has something to do with preventing the tranny from prematurely down shifting when you let off the accelerator.

I have to go now but will be back later on this IMPORTANT subject.
Sam

Last edited by Samuel M. Ross; 03-17-2009 at 02:26 AM.
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Old 07-11-2006, 02:13 PM
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Quote:
Originally Posted by Samuel M. Ross

Do you mean this literally?... if you are you speaking of what is often called the 3-in-1 vacuum valve? Well on both my 240D and 300D MBZs I have concluded this vacuum valve not only switches the EGR on/off but also turns on/off the "bleed" effect of the VCV on the IP. I'm not certain but I think this has something to do with preventing the tranny from prematurely down shifting when you let off the accelerator.
If I didn't mean it, I wouldn't have said it.

They are referred to as 3-2 valves and the vacuum setup on an '84 is different than yours. He can remove everything that goes to the black box.

You can't.
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Old 07-11-2006, 03:20 PM
Cabernet red, actually
 
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Quote:
Originally Posted by Jmana
I just plugged the line going into the pink pod. I also pulled off the cap, and extended the rod fully, so now I have full time air out the centers (which I can control with the slider)
Sounds like you took the dash off. I'm trying not to do that...I think my idea of plugging it behind the CCU might work but the center vents would likely stay closed.

Oh well.

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