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!!!!
===========================================================================================

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! :P ).

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.

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

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

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!

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.

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!

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.

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

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

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.

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)

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

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.

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.

I don't know how it is on your car, but on mine the pink pod was accessible once I had the climate control system out. It's way back in there towards the upper right. I am sure there are other pods that were bad, but for some reason that single pod's vacuum had a significant effect on the shifting of the tranny.

Yes. I did this. After being persuaded by an earlier discussion with Brian I think. It didn't adversely affect the shifts at all. But I can't go so far as to say that I have tested the vacuum levels before and after and found them to be the same. I DO have the correct schematic for my vacuum system and it is hooked up right (minus the EGR removal). Also, I hunted down all vacuum leaks too so it is a tight system now (there was a huge leak in the line to the trunk actuator).

What has me puzzled is that, when in stock configuration I had that weird behaviour I mentioned above. I could attach some pictures, but actually, that was the time I discovered a bb in my line to the transmission. I have since fixed that (made shifts so much better). So I will go test the setup I have now and make sure it behaves like you guys say at idle and under throttle.

Thanks

Where did you get all those different orifices? The dealer? Thanks and good write-up.

Thanks for providing the part numbers for the various orifices:). I typically just swap them out until I get the shift I want.

Yeah, none of my vents open or close at all... I bet this is the heart of my woes. And probably the fact that the little bushing that are in the black box on the engine head are worn to nubs.

See post #8.

It applies to you.......as well.

critical transmission vacumn adjustment
 

I thought I might add my experience to this tale. Three years ago I had a remanufactured engine installed in my '82 240D @ 375,000 miles by an independent shop in Madison, WI. The engine was from an MB dealer, and had been shipped from Berlin. I spent a bundle when all was done. But this car was originally for CA with no rust and original paint in good condition, etc. The transmission had been replaced @ 200,000 miles. When I got my car back, the transmission "flared" between gears and the kickdown switch didn't work (as it turned out, a good thing initially for engine break-in). I took the car back to the shop where I had been having it serviced for ten years, and they said I needed a new transmission and that there were no adjustments possible on the transmission. They had already had trouble getting the transmission to shift, didn't know what to do (called me up and asked if I had any manuals!) but finally compared the internal hook-ups in the "black box" to another 240D that came into the garage, getting it to work. But no resolution on the shift flaring. Funny, because it had worked fine with the old engine. I drove it for 5,000 miles manually shifting between gears to avoid the flaring, while trying to decide what to do, and looking for further information.

Thanks to this forum, I read the Brotherton article and others, and called that business in Florida. I was directed to an independent MB mechanic in Des Moines, Iowa. I live in the Madison, WI area, but did not have confidence in the Madison MB dealer, where I previously had a disappointing service experience. I called the mechanic in Des Moines, explained the problem, and he said "I can fix it - I trained on the 240D 20 years ago!" I drove to Des Moines and the mechanic lost no time in quickly fixing it - checking over the vacumn lines and basically adjusting the modulator on the transmission (which I didn't know existed at the time). Cost: $120. I drove home with the transmission shifting better than it had before. Good thing I got a second opinion. The shop in Madison wanted to sell me a rebuilt trans for over $2,000, and I'll never know whether they were aware of the adjustment of the trans or not. I don't go there anymore.

I now have 396,000 miles on the car, the engine requires no oil between changes (maybe because of my careful break-in), and the transmission is still working just fine. I still have a problem with confidence in mechanics. I had the engine's first valve adjustment at the Madison MB dealer @ 15,000 miles. The service advisor assured me he had two mechanices qualified for my car. The mechanic was a young man who replaced the old valve cover gasket (none in stock) which now permits a faint oil leak around the cover base; lost the plastic retainer on the throttle for the idle adjustment cable, and left the breather hose from the valve cover disconnected. Maybe I will have to go back to Des Moines for further service...

I'm back... with a few responses !
 

"dhbecker" - It sounds to me like by now you should be motivated to roll up your sleeves and do some of this stuff yourself!

"sailor15015" - Yes, the dealer... at least those that I did not have. Your simple "Thanks..." means a lot !

"miner" - If you haven't invested in a " Mighty Vac " yet, do so... for a simple vacuum gage is limited where the hand vacuum pump is so useful testing devices with diaphrams and when looking for leaks in lines you have plugged at the other end. I have raised a few eyebrows driving around with my Mighty Vac wedged between my wipers and windshield!

Back on what to look for with your tranny vacuum. First, use a "T" to hook your Mighty Vac to the line just where it leaves the engine compartment and dives down to the tranny OR if you have extra rigid vacuum line sections and connectors, you could even "T-off" and measure the vacuum right were the line enters the vacuum modulator on the tranny. I read this somewhere!

What you want to see on your gage is a smooth transition from the first vacuum reading....... all the way down to or at least nearly to "zero". Again, if it does not go down that far, then this is an indication that you need to either:
(a) reduce the vacuum back towards the vacuum pump with a smaller orifice [my recommendation] OR
(b) increase the "bleeding" effect by adjusting the Vacuum Control Valve [VCV] that sits on your Injection Pump [IP]. I've looked at the inside of three of these and NOT all are adjustible. The PeterSchmid.Com WebSite has 8 pages of instructions on the procedures and special equipment for performing this task!

Let us know what your test reveals about how the vacuum fluctuates downward.

"scoodidabop " - The last thing you should feel from participating in this FORUM/THREAD is "stupid". The only bad question is the one you fail to ask! I for one will give you all the help I can... either ON the THREAD or OFF if that is warranted! Did you understand Brian's reference to " See post #8 " ?

==========================================

You know when I see terms like "pink pod" when talking about what is affectionately referred to as the "Environmental" system... this makes me cring when thinking about tackling this "broken" system on my Son's 300D. But everything in it's own time. At least he has heat and defog/defrost for the front window!

Chou,

Sam

ok, so my 80 300SD doesn't have any special doodads that control EGR or ANY emissions control devices, all I have is that little green dashpot on my VCV....
http://www.peachparts.com/shopforum/...p?do=big&p=941

the car was shipped sans emissions control stuff......

So " Got_The_Benz ", do you have a question?.............
 

It's a nice photo of your engine compartment. Is that green thingy there your "DashPOT"... aka " Surge Damper " aka " Vacuum Damper "? These are all the different names I have seen used for this vacuum component, and I'm a relative "newbie"!

This brings up a point that has stuck with me as I have had the bad experience of these tranny vacuum control SYSTEMS... namely that there are so many different names being used for the same parts. It's no wonder we often get confused. Thus my strong preference to ask people to first identify the specific diagram or "schematic" from the 30+ different ones at the PeterSchmid.Com WebSite. Do you want to see one that I would not even wish on Brian!? Take a look at this "SCHEMATIC":

http://www.peterschmid.com/vacuum/1977_1985/617_95/1985_cal.jpg

Yes, this baby is a 1985 model fr#&*!@ing "California" car. Thank God my Father-in-Law's 85 is from Oregon! This vacuum SYSTEM not only has a "DashPot"... it has two of them... and a "SwitchOver Valve, Vacuum Transducer" and OH yes just for giggles, a "SwitchOver Valve, Boost Pressure Aneroid". And what the heck is this foreboding thing they call the " Control Unit ". Is that synonymous with "computer"?

The "Deutch" engineers must have just been in the midst of their first crack cocaine party when they designed this “SYSTEM”. I wonder if any of these are still out there and “functioning properly”. Serioiusly, it's no wonder they have gone away from such systems in favor of two and three computers! I challenge anyone to come up with a reference that logically explains what all of these “gizmos” does in the grand scheme of telling the tranny how to shift!

I enjoy a good challenge just as many of you do but for a daily driving vehicle my preference a simple non-turbo 240D!

Sorry about that "Got_The-Benz"...
you deserved better...
do you have a question?,
Sam

Uhhh.. not really, just a little curious what the different colored "dashpots" would do for my car...but yeah, we have an 85 SD at my shop, and it also has (or had) two of those green things...

Actually I like the simplicity of the ' ol dashPots '...
 

for it's my understanding that they serve much the same purpose as shock absorbers do for our suspension systems... they [dashpost] keep the VCV from bleeding off the "tranny control system's" vacuum too quickly.

Before I experienced my MBZ vacuum system " Epiphany " I was even thinking of putting one under my 240D's hood. But now I've been "reborn"... it's the simple life for me. I'm putting "bebes" [sp?] in any and all vacuum lines I see... and some day I want to see the clean lines of my 616 engine's valve cover with nothing perched on its head !

I'm getting silly... time for me to go !

Sam

Thank you, Sam, for feeling my pain. :o

Other than a leak in my climate control system, though, I believe mine is functioning properly. It's clearly taken some maintenance, though. Most of the vac parts are new and the car was regularly serviced by the dealer from '92 to about '03.

I hope to figure out exactly what all those gizmos do one day. I'll have to know so I can figure out what's wrong when things start breaking down. I'm thinking I might have to write a letter to an old MB engineer, though - if any of them survived their alleged crack addiction, that is. ;)

I never thought much about the 'control unit.' Looking at the diagram I'm not sure exactly where it is under the hood. Now I'm curious...research time...

P.S., thanks for the info. Jmana!

Sure, anytime! Just let me know if it helps your shifting problem as much as it did mine. I don't know why the climate system vacuum would be interconnected to the transmission vacuum, but I know for a fact that it is somehow. If you would have driven my car before I plugged that line, you'd think the rear end was going to fall off when the car shifted, and it acted like it had no idea at what rpm to shift at. Now it's smoother than most cars that I have driven. And the only thing I did was plug that one line. On my 87 I went to the vacuum manifold for it's climate system, tested all the hoses going into the manifold with a mitivac, and found a leaky pod, so I just took a piece of plastic wrap and put it over the nipple, and plugged the hose back in, so that's another way to do it without having to access the pod itself.

Transmission vacumn adjustment
 

I have enough time to do engine oil changes, diesel purge, and body maintenance, and that's plenty for me. The rest I prefer to leave to a qualified MB mechanic. I really can't get excited about all the talk about orifices, etc. I did a while back though do an EGR valve (defective) removal/conversion, with advice on this forum from Brian Carlton. Fortunately, where I live emissions tests are not required, and if they are in the future, I have collector plates on the car that will never expire. With conservative driving habits, mileage has improved to 30 mpg from the previous 25 mpg (probably also helped that I specified the A/C be left off - a real money pit in my estimation) when the new engine was installed.

Let's talk "DashPot" or "Dash-Pot" again... " Got_The_Benz "
 

Don't ask me how but while "browsing" for something totally unrelated, I found myself seeing that there is a WebSite/Page known as the:

"Dictionary of Automotive Terms”

So on a lark I asked for the definition for our "dashpot", you know that loveable little inexpensive green thingy usually mounted just above our Vacuum Control Valve [VCV] that is mounted on our Injection Pump [IP]... and low and behold I found two related definitions:

dashpot:
A unit using a cylinder and piston or a cylinder and diaphragm with a small vent hole, to retard or slow down the movement of some part.

dash-pot:
(DP) a diaphragm that controls the rate at which the throttle closes

These definitions have peaked my curiosity such that I might just buy one of these [< than $5] just to see what’s inside. Somehow at that price, I don’t think there is either a “piston” or “diaphragm”... and now that I think about it the green color probably coincides with the green colored orifice which has the smallest I.D. of the six "orifi" MBZ shows for these SYSTEMS… 0.7mm.

I’ll bet ya there is at least an orifice inside this “thingy” that is 0.7mm! In any event I think these were initially added to certain engine/tranny combos that needed to delay one or more of the shifts. For instance what if the tranny shifted well from 1-2, 2-3 but then 3-4 was too quick or as some say “ too soft ”. I can envision such a chamber with small restricted orifice acting to delay the eventual decline of the vacuum the CVC is bleeding off... and this might just correct such a 3-4 shift while not necessarily causing the others to change significantly. My Son's 300D with brand new tranny has such a problem.

Q1 – Has any of your dissected one of these green “ thingy(s) ”?
Q2 – Any other thoughts or ideas from anyone?
Q3 - Anyone want to wager on one of these fixing my 3-4 shift problem?

Just clearing a brain _art,
Sam

Went and put the mighty-vac on the line to the modulator. Got 13 in. at idle and went smoothly to 0 when the lever on the vacuum valve hit its full load stop. This is with a blue orifice and the EGR lines removed. So this seems fine. I am not going to worry about what was wrong before.

Thanks for the posts.
I've been lost in the dark and scarry world of past owner's son selling the Becket, control panel including wood ('79 300 SD) and this thread has shed some light on rebuilding the vacuum system. I now have defrost and heat, blower stays on high, but I've lived through worse in WI winters. Vents would be nice.
Trany shifts fine untill 18-20 MPH downshift which ... clunk.
Thanks again. Please keep this thread alive.

This is intended to be my closure to this THREAD...
 

When I started this THREAD I intended it to mainly cover the vacuum control system for the automatic transmissions on these cars. So when a couple of response POSTs strayed to and included how you had experienced what I will call “interactions” I was not prepared to respond… so I didn’t. This is where a completely different vacuum system causes another to react or not function properly… e.g. someone’s climate control causing the transmission to shift. Well now I have a greater appreciation for such “interactions” and wanted to kind of wrap up this THREAD with these comments about vacuum system “interactions”.

Since I started this THREAD, I had need to hunt down vacuum leaks in the door LOCK/unLOCK system. [ See my THREAD on this at: http://www.peachparts.com/shopforum/diesel-discussion/160169-w123-vacuum-interlock-diagram.html which is now in the “General Information” FORUM ].

What I’m leading up to is the fact that between the vacuum pump and the vacuum brake booster reservoir there are typically two “T”s and I think that most [ if not all ] of these incorporate a restricted orifice in them. Over coffee with my MBZ friend at lunch one day a realization came to me and so I quizzed my friend [40 years of work on these cars] as to what the “other” vacuum users were in these cars. Well guess which one he forgot to mention… YES, the most IMPORTANT… the power brakes!

As a retired safety engineer it had come to me that these “T”s branching off the large, main, vacuum line were restricted because the designers wanted to give priority to the brake system such that you could suffer a failure in any of these multitude of other systems and still have much of the vacuum available for the brakes.

These same restricted orifices also serve to minimize interactions between systems… e.g. the A/C causing an unwanted shift of the transmission. So along come mechanics and owners who correctly clean out the “guck” and crud that ends up clogging these “T”(s) and inline orifices and in some cases they also drill out these “T”(s). The white “T”(s) on the two 1980 cars I show below are about .8-to-.9mm in size and I have seen on this FORUM people recommending they be drilled out to 1/16 inch which is ~1.6mm… and such a dramatic change in size of these IMPORTANT restricted orifices clearly can upset the balance that was designed into these cars… balance that gives the BRAKES their needed priority over other vacuum users… and balance that prevents interaction between unrelated vacuum using systems… the tranny and the A/C.

Just my closing thoughts for this THREAD!

Sam

The purpose of the restricted orifices is to isolate the components downstream of the restriction from the brake system. If there is a failure in a vacuum pod for the climate control or a failure in the EGR valve, the restriction prevents the main vacuum line from dropping too low in vacuum. Most of these consumers use very little airflow and a .9mm orifice is sufficient provided one is willing to wait 15 seconds or so for complete actuation. The time is not a factor for these devices so the system works as designed.

If you were to remove the orifices completely from the system, the system would still function perfectly well, with no interactions between the various systems, provided that there were no leaks in the system.

The sole purpose of the restriction is to prevent a leak from dumping vacuum from the brake system. The size of this restriction is not magical. It depends on the capability of the vacuum pump. If you open a .8mm restriction to 1.6mm, you get 4X the flow, however, this flow is still insignificant when compared to the 6mm?? I.D. of the main vacuum line. I seriously doubt that a wide open 1.6mm restriction would drop the main line vacuum more than 1" of vacuum......or so.

A quick test of a wide open 1.6mm restriction on the main line would confirm or deny this theory.

Brian... I truly respect your knowledge of these cars we Love and sometimes Hate...
 

but as a former safety professional [ now retired ] let me try to make sense using an analogy of what in my former profession is called "Safety Factor".

Way back when steam boilers were blowing asunder, the first design safety factors were developed and these were originally 6… which is to say that the pressure components were designed to hold at least 6 times the maximum operating pressure of these vessels. In more recent times our laws have allowed the lowering of such design safety factors… now to as low as 4 and obviously we have not returned to the days of trains and heating boilers blowing up and killing hundreds of people as was the case in the early days of steam engineering design.

However, IMHO I would not think of serving as a professional witness to explain how it was OK to play around with whatever the safety factor the German engineers designed into what I see as a critical system [because of the BRAKES]. Why do you think by 1985 these same German engineers added a completely separate electric vacuum pump and system just to supply those notoriously leaky door LOCK/unLOCK vacuum elements and lines? IMHO there is a good chance they did this because they had learned of the problems we are still today dealing with... and the designers wanted to remove any possibility that this leaking system could compromise the brakes in their later models. If this had been seen as an emminent problem, today it might have been the subject of a recall.

Yes, I have given professional testimony several times in courts but personally I would not even think about doing such on this subject matter.

I fully appreciate your comments about how most of the vacuum using components... how they are largely "static" and use the vacuum for short periods. The vacuum control valve on the IP that actively bleeds off the vacuum is the only actively "dynamic" vacuum component that I have discovered [thus far]... so yes, most of these components do not use much vacuum air... but in the safety field you must assume systems fail and then try and figure out what will be the results of such failures.

For the same reason they put the two tail lights on separate fuses they [the German design engineers] have been trying to make this main vacuum system that supplies the brakes... trying to make this system as reliable as practicably possible and IHMO these orifices are are a CRITICAL part of their design efforts. Why do you think they built these orifices into the "T"(s) rather than putting them "in-line" separate from the "T" as the other orifices were done... IMHO THEY PURPOSELY TRIED TO MAKE IT HARDER FOR US TO DEFEAT THEIR SAFETY DESIGN.

IMHO the #1 reason these "T"(s) are being drilled out is to clear the dirt from the orifice to restore the system to operation... so it is the need for maintenance and repair that is the initial problem. What I have done is to add an in-line air filter onto the under-the-dash vent... this to filter out dirt from where I see most of the dirt enters the vacuum system. This I learned both from this FORUM and from my recent friendship with a 40-year independent MBZ mechanic.

So IMHO I canNOT recommend to others to go where my professional SAFETY experience tells me not to go... DON't drill out the orifices in the main vacuum line that runs between the vacuum pump and the brake booster reservoir !

Best regards,
Sam

One final thing... a testimonial from a friend...
 

who upon reading this THREAD a short while ago related his experience as to what can happen when mechanics play around with brake booster vacuum supply lines:

"I have to go with your thinking Sam... I have had a massive booster vacuum hose failure at highway speed on one of our Saturn station wagons... It tested my heart rate thoroughly... I heard a backfire and then the engine went full throttle because of the massive unthrottleable air intake into the intake manifold (gas engine)coupled with Little or NO BRAKES ! because of power booster vacuum gone... lucky me was able to coast to shoulder... upon inspection the stupid mechanic shop thought the big booster line would be a good place to put the Vacuum Tee for the cruise control (no clamps either) just pushed onto the hoses... the backfire in the intake manifold blew the tee right out of the booster hose!!... I called the shop that installed it and they said they have hundreds out there right now with no problem...
I asked if he had a good lawyer on retainer....."

So if any of you don't agree to my cautious approach in the interest of safety, then let's agree to disagree and move on to other subjects...
for I would rather be giving back to this FORUM than beating a dead horse!

Sam

There really is nothing wrong with your cautious approach to the subject. However, as an engineer, I don't accept your conclusion because you don't provide a single piece of data to support it. In reality, you do not even have the data that shows the size of the orifice for every Mercedes vehicle that is currently operating.

My SD may already have a 1.6mm orifice in the T. If that's the situation, then drilling out the orifice to the existing 1.6mm would present a result that is no different than the factory intended.

So, while anyone is free to make an opinion on this forum, I'd certainly appreciate it if you toned down the rhetoric and the underlined bold letters because your opinions are not based upon any data and they might just mislead others and cause them unnecessary expense. People on this forum have been drilling those orifices for many years prior to your arrival and not a single individual has reported an unsavory incident due to that procedure.

For the record, I'll do some tests and determine the exact size of the factory orifices on the SD and will subsequently post them on this thread.

I may even drill the orifice to 1.6mm.........if it's not already there.........and measure the vacuum loss with an open line.

Brian,
IMHO I have not attacked you so why the strongly worded POST(s) when I express my opinion?... and why suggest that my free speech should not include bold face and underlining? I noticed you used some boldfacing above. Is it my rhetoric that needs toning down?... for I must say that it is your rhetoric that has touched a raw nerve at this end and I am not intimidated by such. If I'm breaking one of the FORUM's rules by using logic and reason to press home a point for SAFETY's sake, please show me the rule and I'll muzzle my "tone"!
Sam

You've broken no rules and I've made a simple request to prevent you from misleading others who may wish to drill those orifices and save the cost of a new main vacuum line.

As I told you above, folks have been drilling them for years prior to your arrival without any unsatisfactory results. You have ignored this bit of data.

You're free to express your opinion as you see fit. There is absolutely no reason to use boldface and underlining to scream said opinion to the forum.

However, again, as I mentioned above, although you remain adamant that such a drilling procedure should not be done, you've accomplished no testing to prove the unsafe nature of the practice.

Best Vacuum Guage??
 

This was an excellent discussion and answered a lot of questions for me. I just bought an '84 300D that shifts hard into 2, a little better into 3 and very smooth into 4. To get started, I have a few questions:

1. What kind of vacuum guage should I purchase to get started.
2. I printed a schematic diagram of my vacuum system from the peterschmid web site (an excellent resource) for my car but the color codes are too fuzzy to read. Are there any other sources out there for diagrams?

Thanks again for the discussion and any further help.

Richard

1. If you don't have a Mityvac, that tool will be the best purchase you can make. It can test for vacuum or supply vacuum, depending on your needs. The cost of the Mityvac is just slightly more than a vacuum gauge.

2. Here is your diagram:

http://home.comcast.net/~phantoms/va...gr_82_300d.jpg

Thanks, Brian. You guys on this forum are quite an asset.

Richard

Since you have the proper diagram, do yourself a favor and eliminate all the vacuum lines the come out of the #71 plug. Just remove the lines and plug the two T's (or remove them as well). You'll eliminate most of your vacuum problems by getting rid of the vacuum supply to the 3/2 switches in the black box.

OK. If I am reading this diagram correctly, it looks like I am eliminating a vacuum signal to the EGR system. I read references to the 3/2 switches before. Is this referring to a switch that signals a shift from 3rd to 2nd gear or am I way off. Does it all have to do with emissions controls?

I also read references to BB's. I am assumig this means literally BB's that you use in a BB gun because they are the right size.

Yep, the 3/2 valves in the black box serve only to control the EGR system. It has nothing to do with the shifts. But, if it's leaking, the shifts will be affected and will be firmer than desired.

The BB is the perfect size to plug a vacuum line. But, in your case, if you eliminate the T's and connect the remaining lines with a short section of vacuum hose, you'll have a much cleaner setup.

I'll give this a try and see what happens. Thanks for the advise.

Richard, Brian and I are in agreement here...
 

(1) Vacuum Testing Equip - A combination gauge/hand vacuum pump that is metal and thus more durable is in order and I do believe the MityVac fits the bill,
(2) Obtaining the Clearest Diagrams from PeterSchmid.Com - Back to your obtaining the Vacuum Diagram for your '84 300D and it turing out to be a BIT "fuzzy". I too have had this in the past, so I just completed an experiement to test the two different ways I know of that results in a file that you can use to make a quantative judgement of the resolution... namely the "Copy" and the "Save" methods and found that although the easiest way might be the "Copy" method, however for me this resulted in a file of only 45KB size for example the " 616_617_91.jpg " which I believe is for your car [it depends upon what engine you have... the 617.91... or the 617.95 ] and the "Save" method resulted in a file size of 113KB. So unless you used the "Save" method, you might not have the best clarity possible from the PeterSchmid.Com resource.
So here is the SAVE method:
(a) Go through the menu/pop-up windows until you have the diagram you want... and if your engine is a 617.95, you will also need to know if it is a CA car [I hope not] or a "Federal" car,
(b) Initially left click on your graph selection while it is still small on the screen... this will expand the graph until it mostly fills up the screen,
(c) Right-Click on the graph and you will see several possible selection choices: "Save" "Copy" "Print" etc.
(d) I recommend you "Save" this file to your hard drive... and later use the file to print later. Make sure you are using the higher resolution options that most printer "driver software" offers... and if this still does not quite give you the needed clarity, you might want try a special "photo" paper to squeez out a little more.

I don't trust the print resolution you obtain from printing something via an OnLine link. Don't ask me for a technical reason why... I just don't. This suggestion is purely based upon the different file sizes I obtained a short time ago while experimenting with these two methods. Give this "Save" method a try, print it, and let us all know if you think there is a significant improvement. If there is, many of us will benefit the next time we download a vacuum diagram from PeterSchmid.Com.

Regards,
Sam
P.S. - To all who have read my all-too-often lengthy POSTs... my excuse is that I type at ~100 words/minute! This is not to brag... just an explanation of my affliction that I'm happy to have for it has also helped me tremendously over the years !

Richard, I'd love to know for certain which diagram...
 

you are using and the best, most definitive, way is to obtain and pass this along to us on this THREAD is to:
(1) Right-Click on the enlarged diagram,
(2) select the "Properties" in the pop-up window and then you will see the "URL address" in the middle of the next pop-up window you get,
(3) triple-click with your cursor somewhere on this URL address and this will highlight/block the entire address,
(4) then it's the normal copy and past

For e.g. - http://www.peterschmid.com/vacuum/1977_1985/617_95/1984_1985.jpg

This way I can follow along with this lesson... and maybe even contribute.

Sam

Pardon me gents but I find myself playing catchup here...
 

Brian,
I now see the diagram you posted earlier that appears to come from a file with the HTML address of: http://home.comcast.net/~phantoms/vacuum/egr_82_300d.jpg that I'm guessing is a personal WebSite of some sort... and although Brian's diagram is named as though it is for a 1982 300D "EGR" system, it appears to be all but identical [except for how the text legend is formatted ] to the one at:
http://www.peterschmid.com/vacuum/1977_1985/617_95/1981_1984.jpg. This latter diagram is for 1984 "Federal" and 1983 CA cars with 617.95 engines and is labeled as such right in the graphic. Brian's diagram has no application lable on the file's graphic.

Most important, I notice that Brian's diagram has considerably higher resolution which gives better clarity.

Brian - can you tell me the original source for your diagram?... also I'm puzzled as to how you were able include such a high resolution graphic right in the body of your POST? That must be the "Attachment Management" feature that is titled "Upload file from a URL"??

Sam