The box only regulates EGR on your vehicle. Sam doesn't restrict his comments to specific vehicles..........speaks in generalities for all vehicles.

Remember this THREAD is about the "Tranny-shifter Vacuum Control System"...
 

Charles,
1/ Remember this THREAD is intended to help those struggling with what I have come to know and label the automatic
"Tranny-Shifter Vacuum Control System". So as you get into other issues you need to either find an active THREAD on that issue(s) or start a new one. Let me just say I'm surprised you are painting the car before you know whether or not you are facing a major expense on internal tranny problems! As to the A/C, I'm fast learning about the ACC(s) in these cars but will NOT be up to speed on the later model ACC system I believe to be installed in your car. I do now have a 2-disk set of the 2003 edition W123 chassis manuals which includes the ACC system you have. I'll see IF I can find a vacuum diagram for your ACC. Let me say something in general that I think is very useful. When working on any of the 3 distinct and separate vacuume control systems on these cars, while working on one system I would advise disconnecting and plugging up the other two... for I feel this can make for far less frustration in diagnosing problems. And then when each system works well on its own, then you can bring all OnLine and work out any interaction problems between systems. (a) Tranny-Shifter, (b) ACC, and (c) Door-Locks.

2/ - Here is the response I get back when I try and run a check on your VIN:
Datacard for VIN WDBAB33A6DB031332 is not found
1) VIN was misspelled in the request form;
2) VIN was erroneously read from vehicle body or documents;
3) VIN is not of an original vehicle and was forged by criminals;
4) The vehicle was produced in late 2005 or 2006, and is not included yet in our database
But from your description above, I'm all but certain your car is a 1983 "300TD" [NOT "300D" which ended I believe in 1981] with a 617.952 engine... and this means that the vacuum diagram for your Tranny-Shifter is most likely this one found at: http://www.peterschmid.com/vacuum/1977_1985/617_95/1981_1984.jpg
IF you are unable to download, print, and read all of the text in this diagram, let me know. This diagram is labeled such that it is for "1981 to 1984 (Federal)". I understand you bought your car in Texas, but check and read the pollution control stickers under the hood and make certain you do NOT have a devil of a California car! I know one reader in NY had a car delivered there that turned out to be a California car... it can happen.

As to the elimination of the "Black Box"... again I recommend this NOT be done until you better understand how your Tranny-Shifter System functions so first read the legend in the vacuum diagram and for components #64a & #64b and you will see that these two function as part of the Tranny-Shifter system as "idle speed shut off" and "full throttle shut off" and from reading the routing of the vacuum plumbing this is referring to shutting off the bleeding effect of the VCV. I agree, IF you can get away with it in your STATE, go ahead and disconnect the EGR system. Brian might still have a kit that will blank off bothe intake/exhaust manifold openings IF you want to physically remove the EGR... otherwise just plug/remove the vacuume lines but also make sure the EGR valve does not leak exhaust into the intake or the intake is sucking too much air through a hole down below.

I'm looking forward to your getting back to the Tranny-Shifter system on your multi-project car!
Regards,

That's the right diagram.
 

Sam.
Thanks again for your interest. That is the correct vacuum diagram. I had to enlarge it to try to read (62 year old eyes). I could follow the diagram and it is an exact match. I could not read some of the letters and numbers. Except: I see the 64a and 64b but the other numbers on that section are not clear (56 & 69? - not in the legend). I've not spotted that under the hood - is that the manual shut off device also?

On your other points:
1. Yes, I'm following other threads. The one on climate control is about as involved as this one. The reason for the repaint is as follows (and offered just for interest and background): The shifting nature has been the same since the transmission was rebuild 15 years and 103k miles ago so I have no reason to think a rebuiid will be needed soon. I've decided to keep the car (I've had it since 83, maybe it will last another 25). For the last 10 years, it has been my daily driver and even though I have kept it maintained mechanically, I had ignored the cosmetics (faded paint, cracked dash, etc.) thinking I would drive it till it totally quit. In January, it got hit on the passenger side by a lady pulling in to park next to it. Dent from front wheel well to rear but doors still work and no structural damage. Her insurance is covering the repair. I was considering cashing the check and junking the car. In researching that decision, I found this forum and got inspired. Took a second critical look at what I had (great running engine, totally maintained suspension, brakes, etc. - interior shows no wear except for the drivers seat, broken visor mirror, and a cracked dash - exterior has no rust and never has, new damage to the passenger side, badly oxidized paint). Given that I'm the original and only owner and almost the only driver, I think the forum members would see this car as a keeper, right?. I made a deal with the body shop that I would do the R&R of the trim, bumpers, windshield, etc. and in return they would refinish the entire car for not a lot more than what the insurance will pay.
2. This VIN thing only has me slightly spooked since I bought the car new. I confirmed that what I gave was correct. So maybe it is the model designation. The rear badge reads 300D. Wasn't the 300TD a station wagon? I went in to my records (25 years worth) and pulled the original window sticker, owner's metal badge, and ID card with key code etc. On the window sticker, it reads Model: 300D-T 5-PASSENGER SEDAN ENGINE; 3.0 LITER OHC 5-CYLINDER TURBOCHARGED DIESEL. On the owners metal plate, it reads: 300D-T also and what apprears to be body and engine numbers: 123133-12-031332, 617952-12-052378. I read the emmission control sticker under the hood (first time ever) and the bottom line states that "this vehicle conforms to USA EPA and State of California standards for 1983 vehicles". Damm, what does that mean? The window sticker shows Houston as the port of importation and vehicle prep. ctr. I don't see any devices other than the EGR. What should I look for to identify a "devil of a California car"? The vacuum diagram you sent matches, but it does lead to other vacuum lines with multiple branches near the firewall.

What was becoming a dog of a car has now become a wonder four generation family bonding effort. Involved in the project are my father (87 year old WWII veteran and retired diesel tractor mechanic), my self, two sons, and two grandchildren. They all have taken on tasks and the biggest agrument is between the grandchildren ages 5 and 8 over which one will eventually get this car. Even if we encounter major expense for a transmission rebuild, the value of quality family time spent working together will more than compensate.

Charles

PS: Thanks again for your help and this forum!

You lucked out... 1983 California Tranny-Shifters are the same as "Federal"
 

Charles,
Your last POST has a lot to review in greater detail... but for now it looks like you lucked out... assuming you do have what sounds like a California car, then taking a look at this address: http://www.peterschmid.com/1984_617.htm will confirm that the 1983(s) were the same as the Federal car! Your lucked out. The 1984(s) and particularly 1985(s) were NOT so lucky!
Back to ya later,
Regards,

Better Image
 

For some reason, this link allows me to get a clearer image than the previous link. I can now read the numbers better and this is the right diagram. I've not found parts 68&69. Are they under the hood?

Thanks again,
Charles

This THREAD is about the "Tranny-Shifter Vacuum Control System"
 

For the Readers of this THREAD,
I am trying to help Charles from Texas [" Cr from Texas " ] OFF-FORUM with a multitude of projects and problems with his MBZ that are not directly related to the topic of this THREAD.

Please try to NOT to "glum" onto this already lengthy THREAD and discuss other topics... for this complicates those who SEARCH MercedesShop.Com's WebSite for answers to problems they have. IF the subjects/topics discussed on this THREAD drift too much and too often, it can cause readers NOT to find what they need... a way to come to grips with what I see as one of the most common and frustrating problems with the automatic transmission equipped diesel powered W123 and W126 cars... and to a lesser degree other model diesels as well.
Thank you for you cooperation,

Is the vacuum supposed to taper in a linear fashion from high vacuum at idle to 0 or near 0 vacuum at some speed?

Or is it more digital in nature, such as 8" at idle through 2Krpm, then 0" at 2+

Interesting "handle" there "12MPGHWY" !
 

"12MPGHWY" - In general I understand what is meant by " linear " -vs- non-linear and in this case, I must assume that you mean the " bleed " that the VCV performs upon this control system... namely that it would produce an equal amount of vacuum drop [expressed in inches of mercury] for say each 10 degrees of rotation as the throttle linkage rotates the VCV's actuator shaft... and to this presumed question I would say NO. This is based strictly upon my knowledge of the internal components and workings of the VCV. IF you were to instrument and analyze how the VCV performs it's task, I would expect it to be at least slightly non-linear on a graph of "Inches of Hg -vs- degrees of rotation of the VCV shaft.

As to what you mean by " Digital in nature " as applied to this "Tranny-Shifter Vacuum Control System" and/or the VCV's variable bleeding action it has upon this "Tranny-Shifter" control system... well I'm sorry but I have NO idea as to what you mean!? I would expect more often to see "Digital" -vs- "analog" to be the comparison made and this is most often in all kinds of electronics... e.g. Digital TV broadcasts !

Maybe IF you give us a description of your situation and/or problem and/or symptoms, we can understand better!??
Regards,

Here is another take on "12MPGHWY's " question...
 

"12MPGHWY" - Here is another way I would like to answer "around your question" for I'm still NOT certain I understand it.

I think the " latitude " of what vacuum pressure you start at in the line leading down to the tranny's modulator and what you end up with at higher sustained throttle positions going down the highway progressing finally to 4th gear... I think this " latitude " or "range" of acceptable start/finish vacuum readings is variable in large part depending upon the age and internal conditions of the transmission and maybe to a lesser degree some of the main components in the Tranny-Shifter Vacuum System... e.g. VIVO, and modulator. This is why I am very interested to try hand pumping the vacuum the tranny's modulator sees to test and find out what specific vacuum the car needs at whatever speed, gear change, and/or load condition I'm interested in resolving a given objectionable shift problem. Given this manually created vacuum reading that seems to solve the problem or make it less objectionable... given this, then I feel I would be far better equipped to help owners with older baby-boomer aged transmission problems.

On one final vane, I think you could have taken these cars off the MB new car assembly line those many years ago and then run them through a line of the best and brightest MB engineers and I think these cars [ especially the pre 1983 models]... I think these cars would shift a bit rough compared to the 1985 models with all their add-on components that refine the vacuum shifting control system. Contrary to what some people have expressed at times [ myself included at one time ] I think additional components on the 1985 W126 300SD's [ and the W123 models that has the same external shifter system]... I think these cars do a far better job at shifting smoothly. I say this more readily after I have looked at a side-by-side comparison between these two "Tranny-Shifter Vacuum Control" diagrams:
Compare the simplicity of this system which did not even have an EGR on all of the applicable models: http://www.peterschmid.com/vacuum/1980/123_1.jpg
with the complexity of this: http://www.peterschmid.com/vacuum/1977_1985/617_95/1984_1985.jpg
and yes, I have purposely excluded the 1985 California edition at: http://www.peterschmid.com/vacuum/1977_1985/617_95/1985_cal.jpg
which is the granddaddy of complexity having I believe ~5 additional components including the dreaded "CAT" [ catalytic converter ] !
This car [ and my in-laws have one for me to try and help maintain] was the epitome of what can go wrong when you try to apply technology before it is ready for the consuming public... and the mechanics who try to maintain them.

Personally I like our two 1980 240D & 300D Tranny-Shifter Vacuum control systems for I have learned to communicate with the system and much more precisely control my shifts by letting off and reapplying the throttle... but my Wife will never be able to do this you see so for many the later models are better. And I have little doubt that my quasi-manual foot shifting technique will extend the life of the tranny! Oh yes, I did effectively add vacuum dampening "dashpots" to these cars and this helps to soften the 1-to-2 shifts some.

Sorry IF I went off on more than one tangent here!
Regards,

You answered my question.

I mean digital in the literal sense as in on or off, the polar opposite of linear.

What I was thinking of was using either a 0-5V proportional valve, or a 12v PWM valve.

The 0-5 volt valve would be easiest, and required on a very basic circuit.

A PWM would work the best, be the most tunable and be more complex.

either way the valve would take place of the complex OEM method of varying the vacuum. It would go between the vacuum pump and trans bypassing the "variable leak" system.

The system would be easy and cheap to design, what I would need to know is what parameters to base the variance on, such as throttle position, rpm, manifold pressure, road speed, or a combination of multiple inputs.

In fact, the combination of a few off the shelf components would do it. Some electronic boost controllers use a simple 2D rpm to duty cycle variance, with several adjustment points that interpolate.

... digital tranny-shifter valve...........!?
 

Well you are out of my league when it comes to modifying these old vintage diesels. Again, I don't think there are precise input parameters by which you can then convert them into a signal that would be used to vary the vacuum to the tranny modulator. As I previously stated above, I think the varible vacuum needed for each of these old trannies is also a variable depending upon the condition of the tranny.

It might help IF we knew what YR/MODEL you are talking about and complexities of your particular "Trannyj-Shifter Vacuum Control System"

Right now I'm installing a combination digital ammeter / Analog Volt-meter that fits into the space of the ashtray & cigarette lighter... and IF you ever build one of these babies you are speaking of, I'll be happy to test it for ya ! I'm not at all sure that such a project is worth the effort and expense. Most modern transmissions might very well have such shifting but they have multiple internal solenoid/ hydraulic valves.
Regards,
Sam

PWM explained here better than I can explain.

http://en.wikipedia.org/wiki/Pulse-width_modulation

Sensors would need to be added most likely.

Your probably right, its probably better to just work with unit as it comes stock.

Much tweaking and still not right
 

Well here I am back again after spending quite a bit of time and experimentation tweaking the vac system on the 300TD and still dont have a satifactory result, I am starting to wonder if my VCV could be at fault, roughly how much vacuum should the VCV be bleeding off, Mine as Brian pointed out is the one used on later turbo diesels and I am trying to use it on an 81 tranny, perhaps I would be better off fitting the plastic type from the earlier models, Is it right that these are adjustable to increase/decrease the amount of bleed, could anyone furnish me with a part number for this valve? thanks

Felix

Where are you installing the orifice to limit the vacuum to the VCV? It's got to be upstream of the VCV.

What's the diameter of the orifice?

With a proper orifice, the vacuum should fall rapidly when the rack is opened.

You'll need to T into the modulator line and route the gauge into the vehicle to monitor the gauge while you drive it.

have tried four different orafices, not sure of the exact diameter, the colours were red, yellow, blue, and green, I tried them in the line directly downstream from the main tee in the brake booster hose, will try teeing into the modulator line and reading the guage whilst driving and will report back, thanks for your quick response

Felix

Umm I need to clarify what is meant by upstream and downstream here, starting from the vac line at the main brake booster hose heading for the VCV is this heading down or up, pardon my question ?

The orifice must be inserted in the line that goes to the VCV. The vacuum at idle should be approx. 10" or so and it needs to drop from there as the rack is opened. If the orifices don't affect the results, the VCV may be non-functional.

The main vacuum hose is upstream of the VCV. The orifice must go ahead (upstream) of the VCV.........between the main vacuum hose and the VCV.

Yes I thought so. I have tried this and the orafice does not affect the high reading the only measure I came up with to reduce the vaccum reading is to wind in the throttle cable partially depressing the 3:2 valve on the cam cover thereby bleeding off all the time this kind of produces the desired effect but only on warm engine as soon as I start again from cold I am back to square one i.e very late shifts, I did try fitting a ballafix valve ( on off water valve) on the modulator line to act as a further restriction but this did not really achieve the lower reading consistantly either, as you suggest I will tee into the modulator line and read the guage whilst driving and report back

If your problem is late shifts.........the vacuum level most likely will not help with this.

See if the vehicle has a Bowden cable. This cable is attached to the throttle linkage and is tightened as the throttle is opened. It leads down to the transmission and is usually on the right side of the engine.

This cable affects the timing of the shifts and it can be adjusted if you can find it.

No cable but now that you mention it there is two nipples on the throttle arm as though a cable should be there, did the cable supercede a rod arrangement? my 280 coupe has a rod that goes to the transmission tightened by the throttle action, incidentally, the transmission on the coupe and the one on the TD are identical looking apart from the arm and rod arrangement, what is the purpose of the cable/rod, is it to do with shift timing? I assumed it was to do with the kickdown, could I retro fit a rod or cable to my TD transmission? I have a spare rod and arm that came with a transmission I took from another 280 Coupe as a spare for mine, I ought to be able to fabricate a linkage from my throttle arm to the rod fairly easily if this is the answer, it could be that the original rod has been removed previously for some reason I will have to make a closer inspection. perhaps this is where I have been going wrong all along ie a vital part of the setup not present ?

Felix

It's very difficult to help you because that vehicle appears to be very different from those over here and, furthermore, it doesn't appear to have all its hardware.

The older vehicles had a rod and bellcrank affair. This was subsequently replaced by a cable in later vehicles.

In any case, this mechanism serves to delay the shifts. If the rack is opened a large amount, the transmission will remain in the lower gear and allow the engine to rev reasonably high.

yes and It probably does not help that I have matched an 80/81 tranny to a an 82 engine with bits and pieces and guesswork ie not sure if the bits I have will work together anyway, kinda wish I hadnt started the project, but that just makes me more determined to finish it. thanks again for all your help though much appreciated

Felix

Going back... did you test the VCV...
 

Felix - Have you tested your VCV as I have recommended? Since your VCV is so different from what we are accustomed to seeing, I think this would be appropriate... I would put the hand vacuum pump on the port [where a line is connected]... on the port that goes to the tranny vacuum modulator. Pump the vacuum pump to see if the vacuum holds. For the sake of continued discussion, I'm going to assume it does NOT hold the vacuum. IF this is the case, then put you small finger over the "vent" port connection that normally runs through the firewall and then ends with the line open to the atmosphere. Put you small finger over the vent port while you pump the hand vacuum and see IF it holds vacuum.
Report back on this... for we must find out why you are unable to successfully bleed down the vacuum on the Tranny-Shifter Vacuum control system's vacuum.
Regards,

Some closure at last
 

My "INDY" [ Independent Mercedes Mechanic ] sometimes says...
 

Felix - So vintage diesel Mercedes in GB have 4 different models of VCV(s) and similarly you have matching color coded transmission modulators. I'm a little surprised the German engineers didn't create RED - WHITE & BLUE for us here in the U.S. - My Hungarian "INDY" friend here in the U.S. often laughs and jokes about such things on these cars as being are examples of " Hitlers Revenge " !

In any event you have proven the original title of this THREAD to be accurate... that it is critical to understand the vacuum system on these diesels vintage Engine/Transmission-Shifter Vacuum Control Systems... and to [ one-at-a-time ] systematically isolate any problems with it. And yes, understanding how vacuum is NOT really negative pressure but rather it is pressure below 14.7 psi [ 1 "Bar" ] and that very similar to electrical circuits until air flows in a vacuum control system, you WILL NOT see andy pressure drops... so there is the STATIC state and there is a DYNAMIC state in vacuum control systems. AND YES, these trannys do shift a bit "stiffly" until the fluid has warmed up some !

Thanks for letting us all know how you solved your car's problem there on your side of " the pond " !
Regards,

Most diesel vintage mercs in the UK had manual transmission, The auto set up, notably the colour of valves (which I now know to have different vacuum dumping properties), addition of a rod or bowden cable coupled with triangular throttle linkage etc varies according to year the earliest being the simplest much the same as it does on the US set up, I am guessing here but I think the white plastic VCV was developed specifically for US cars to work in conjunction with the black box and EGR system, Guessing again but the addition of a rod or cable would help to eliminate the rough late changes on cold fluid by adding some persuasion to the change other than just vacuum. anyway the car is going on a 200 mile round trip tomorow before it is passed back to its owner and then the next project looms a FWD audi a6 TDI engine rebuild Oh joy :)

leaky vacuum transducer
 

My '87 300tdt was not shifting right so I checked the vacuum line coming off the vacuum transducer and leading to the transmission modulator. No vacuum. Incoming vacuum line was checked out OK. Where happens in the transducer?

Wes

.......... We need a Vacuum Diag for your Car..........
 

Wes,
Your car is newer than any others we have tried to help with this THREAD and when I look at: http://www.peterschmid.com/vacuum.htm, my favorite resource for vacuum diagrams does NOT cover your model [station wagon?].

So IF you can identify a source for the Tranny/Engine Vacuum Control System in your car, otherwise you might not find much help. Meanwhile, I'll look elsewhere to see what I can come up with!

Q - Is your car a W124 or W126 chassis?

Oh, I see... it is a 300TDT W124 with the 603.960 engine... right?

Regards

Hard shifts -- 1987 300D (W124 w/OM603)
 

My '87 has had "extra-firm" shifts for as long as I've had it. At very low throttle positions the shifting is reasonable -- it usually gets harsher as the footfeed is pressed down. Road speed does not seem to matter. The shifts are not always harsh but can involve any upshift (1-2, 2-3, 3-4). Downshifts are OK, almost always unnoticeable. The trap ox recall has been performed and the entire exhaust system including the turbo replaced. The EGR system has been blocked and removed including all of the vacuum stuff. There do not seem to be any vacuum leaks in the car. Boost has been measured at 11-12 psi at the manifold. I've done the following to try to understand the problem:

Engine off

1. Remove windshield washer reservoir and inspect the Bowden cable where it connects into the throttle linkage and goes down to the transmission. With no footfeed at all, the cable is neither slack nor under tension. As soon as you start to press on the footfeed the Bowden cable sees some pull. Pulling on the cable by hand reveals some spring resistance, suggesting that there is something on the other end, i.e., the cable is at least not dangling under the car somewhere.

2. Disconnect transmission vacuum line from the green dashpot; connect Mityvac to vacuum line, pump down. Read 28 Mityvac inches of mecury, steady with very little decrease over a couple of minutes.

3. Reconnect green dashpot to transmission vacuum line using a tee and connect Mityvac to the tee.

Start engine

4. With engine idling, the vacuum on the transmission line is about 16" Hg. It decreases as the throttle is advanced, to a minimum of about 7" Hg.

Stop engine

5. Mityvac continues to read about 16" Hg in the transmission line. Pushing the throttle to the stop drops the vacuum in the transmission line to 7" Hg. Releasing the throttle sends the vacuum level back to 15-16" Hg.

From what I have been reading here, it seems that the Bowden cable is set correctly, the VCV is working (with possibly a little too much vacuum) and the modulator is not leaking. Yet the shift remains unacceptably harsh.

What should I do next?

Jeremy

Jeremy,
I have zero experience thus far with Bowden Cables... and the same for the turbo(s) on these vintage MBZ(s)... so IF either of these are a factor for you, I'm afraid I would probably NOT recognize it !

The thing I find most intriguing about your POST is in paragraph #5... where you say the vacuum reading keeps coming back after the engine is shut down. IF I can get either of my cheap Harbor Freight vacuum pumps/gauges to work for me I'll have to test my 240D to see IF the vacuum control system performs anything like this.

Q1 - Is your "tranny shifter vacuum control system somehow cross-connected such that it receives vacuum from your car's vacuum reservoir tank?...
and
Q2 - Does your 87 [ what model ? ] diesel even have a vacuum reservoir?

Sam Ross

A1 - I think the vacuum system is 'wired' correctly but I'd be happy to have someone show me that I was wrong.

A2 - It's an '87 300D-T (W124) -- the one in my signature line. It must have a reservoir somewhere because
(a) I have a vacuum gauge permanently installed in the line that feeds the shutoff on the IP. The gauge typically shows 15"-20" Hg after the engine is shut down, and
(b) the shutoff on the IP is forceably kept in the "off" position -- you can feel it -- even after the engine is shut off.

So there's a vacuum reservoir somewhere. One of the vacuum diagrams in my collection shows a line leading over to a reservoir in the right front fender. I have such a line but haven't confirmed that there is a reservoir there yet.

Many of the posts in this thread suggest that the correct vacuum level on the tranny line is 8"-10" going down to near zero at full throttle. However, these posts then go on to say that more vacuum causes slipping. I have the opposite problem, so I'm not sure what to do.

Since I have to do something, I plan to first tighten the Bowden cable to see what happens and then play with the vacuum system, maybe adjust the VCV to see if I can lower the vacuum in the tranny line, see what that does.

Jeremy

Yes, you've properly determined that the VCV and the amplifier are both functional.

Please disconnect the line from the modulator to the amplifier and plug the line (from the amplifer). Connect the Mityvac to the modulator line and pump it up to 15" or so. Run the Mityvac into the cabin so that you can take it for a drive. Drive it and keep the vacuum at 15" (approx.) for the entire test drive.

Report back with result of shift quality.

Thanks Brian for being there with your expertise...
 

Brian,
I was hoping that you were still monitoring our TREAD here for I know you are into these W124 models!
I just wish the vacuum diagrams for these W124(s) were more readily available OnLine. By-the-by, my favorite WebSite for such has changed it's name... from: http://www.peterschmid.com/ to http://peterschmidtransmission.com/ .
But there are no W124 model diagrams there !
Does anyone out there know where we can access the W124 Tranny Shifter Vacuum Control diagrams OnLine?

Brian... I have NOT yet found anything to explain something about your "amplifier"... I presume it is a vacuum amplifier?
Can anyone offer an explanation as to what this component is?
Sam

Brian, I will try your experiment with the Mityvac on the transmission vacuum line this morning and report later today.

Sam, I have attached a vacuum diagram that is the closest fit to my 1987 300D-T (W124, OM603) that I have been able to find in the FSM CD-ROM.

The purpose of the vacuum amplifier (inferring from the name) is to provide a wider range of vacuum changeability than what would otherwise be available from the VCV. How the vacuum amplifier works to do that I have not yet figured out.

You will see a vacuum reservoir in the right fender. I have not confirmed the actual presence in my car of this reservoir but the thick line to it is definitely present. It would be the reason why there is vacuum on the transmission line even after the engine is stopped.

I'm unsure whether there are vacuum orifices in the lines at the tee located directly above switchover valve Y29.

I will be the first to admit that I don't understand how this rat's nest does what it is supposed to do.

Jeremy

... Jeremy... you are almost a neighbor... I'm in Novato, CA !
 

Jeremy,
As I expected, the vacuum diagram file you attached to your last POST was only 38K in size... thus the resolution was less than desireable. IF you look and see that the original file is larger than 38K, would you please send it to me by the direct email route at: MrSafety2@Verizon.Net !

This is a whole new dimension for me as I learn more and more about these Tranny Vacuum Control Systems

Sam Ross

Mityvac results
 

Sam, the diagram is "in the mail." About 2 Mbytes.

OK, I tried Brian's suggestion to put the Mityvac on the transmichigan line, pump it down to 15" Hg and drive the car. Results -- butter smooth shifts! I wasn't driving with a lot of throttle, I suspect that had I floored the accelerator and made the car shift at 4500 RPM there might have been a little flaring. But it was great to be able to drive without having my neck almost snapped.

I also tried different 'amounts' of vacuum. Lower than 10" Hg caused harder shifts. This suggests that the VCV on my engine is dropping the transmission vacuum level too quickly in response to the throttle. I'll tee the Mityvac into the transmission line and take some more readings.

Procedure 07.1-1826 in the FSM is entitled "Testing and setting vacuum control valve." For the 603 engine, it specifies 385 +/- 25 millibars of vacuum in the line to the transmission with the engine at idle. This is equivalent to 18.45" Hg. When the engine is switched off and the accelerator is moved all the way to the full-load stop, the vacuum is supposed to drop to 0 mbar (atmospheric pressure).

In my car, the vacuum starts at about 16" Hg but drops only to about 7" Hg at full throttle. I'll try the adjustment procedure specified in the FSM (with accelerator at the full-load stop, loosen the VCV fastening screws and turn the VCV clockwise "until a resistance is felt," then tighten the screws.

Jeremy

385 millibars is equivalent to 11.55" Hg. With your vacuum at 16" at idle, the system should have more than sufficient vacuum for very soft shifts. My 603's are all about 12" at idle and I've attempted to get them down to 10" for firmer shifts.

So, I suspect that the modulator has been adjusted to a much higher pressure than desired because very high vacuum is required to soften the shifts.

Getting better . . .
 

After adjusting the VCV per the FSM, I tee'd the Mityvac into the transmission line and took the car for a drive. The results were: much better (softer) shifts at low throttle positions, still very firm at or near full throttle. I suspect that is proper -- you wouldn't want the transmission to shift slowly with the engine at 4000 RPM.

The vacuum level drops from the idle position of 16" HG to about 5" Hg at full throttle, not the zero level that the FSM says it should be. I don't know if I have a problem with the vacuum amplifier, with some other part, or if the FSM section really doesn't apply to my car.

How does one adjust the modulator?

Jeremy

The amplifier drops the vacuum from 5" toward 0" when it sees boost from the ALDA line. Check to be sure that this line is intact. There is a Y connection at the ALDA for the pressure supply to the amplifier.

If you've got acceptable shifts at all pedal positions, it's not critical that the vacuum level drop all the way down to 0".........if it works well........leave it alone.

The modulator is adjusted with a retractable T handle right on the valve. But, I wouldn't bother with it if you've cured the hard shifting problem.

Finally I understand
 

I'll check the boost line for the appropriate pressure, thanks.

[edit] Boost is getting to the amplifier. With the engine at operating temperature, the vacuum level to the transmission drops to below 5" Hg at full throttle (the Mityvac is not calibrated below 5) so I think the system is working as it is supposed to.

Last night I re-read my collection of Mercedes manuals. In addition to reinforcing in my mind Mercedes' assumption (that readers of any one manual know about and have access to all of the other manuals), I finally figured out how and why the transmission vacuum system works. At least I think I did. Bear with me . . .

When we forum members use the generic term FSM (Factory Service Manual), we usually mean the "how to fix it" service manual for the engine (and I use it in that meaning here). As we become more experienced, we discover that there is also a maintenance manual, a body manual, a climate control manual, and others. One of the "others" that I have found most useful is the annual "Introduction into service" manual. It not only gives service information for models new in any particular year, but goes into more detail than the FSM.

Speaking specifically of the 1987 300D Turbo (W124) and the 86-87 300SDL Turbo (W126), which uses the same OM603 engine, the 1987 "Introduction into service" manual has almost nothing on the 603 engine. Why is this? Because the 603 was new in the 1986 model year, even though most cars sold in the US of A were imported in Fall 1986 or later and sold as 1987 models. Thus, to get the complete poop on the 603, you must read the 1986 "Introduction into service."

As regards the transmission's "temperature and boost-pressure-dependent vacuum control" (the subject of this whole thread), it gets worse: on page 179, the 1986 Introduction says that the vacuum control system "is the same as on engine 617.95 (model year 1985)."

So it is in the 1985 "Introduction into service" manual that one finally finds the how and why of this vacuum control system. This is covered in the section on the automatic transmission fitted to the 1985 300D (W123) and 300SD (W126) on pages 97 through 106.

The section on the "Temperature and boost pressure dependent vacuum control" includes the how and why and pictures of the components including the "Vacuum transducer" (we have been calling it an "amplifier"), the "Coolant temperature switch," the "Switchover valve," and the "Aneroid compensator (Alda). The heart of the whole thing is on page 102, the "Functional description" and the "Turbo boost pressure effect."

As simply as I can put it, the "transducer" uses vacuum from the vacuum pump, more vacuum from the VCV, and boost pressure from the intake manifold to create a vacuum signal that controls the "hydraulic modulating pressure" in the transmission. "More vacuum" gives softer shifts while "less vacuum" gives harder shifts. (This is why the transmission shifts hard when a vacuum line falls off.)

Below 50C coolant temperature, the "Coolant temperature switch" turns off the vacuum signal from the VCV at the "Switchover valve." Instead, the transducer gets (more) vacuum from the vacuum pump. This has the effect of increasing vacuum to the transmission, softening the shifts while the engine is cold. Once the coolant temperature rises above 50C, the switchover valve is turned on and the VCV controls the transducer. An increase in throttle produces less vacuum to the transmission, thus firming up the shifts.

Turbo boost pressure from the intake manifold also has the effect of reducing the vacuum produced by the modulator. Thus, as the engine develops more power, the shifts get firmer (to prevent slipping). All of these "signals" (throttle position, turbo boost, coolant temp, and vacuum from the pump) must be present and in the correct amounts for the transducer to do its job and control the transmission.

One final addition: sometime in 1987, the factory added a "no load" microswitch to the throttle linkage. This switch turns off the boost pressure signal at the transducer when you take your foot off of the accelerator. The resulting increase in vacuum to the modulator helps the transmission to not 'clunk' as it downshifts (such as when you are coming up to a stop).

Anyone struggling to fix this vacuum control system would be greatly helped by access to the information in the 1985 "Introduction into service" manual. I can scan pages 97-106 into a PDF if someone can help me get it into the forum.

Sorry to be so long winded but as Sam said at the beginning, "it's critical."

Jeremy

Hello,

Sorry if this has been asked already....hate to beat a dead horse,but... I’ve skimmed thru the entire thread and can’t find a similar Q or A.

It’s always stated that the vacuum should drop to zero or near zero with the VCV at full throttle. How “near” zero is acceptable? I can only achieve 5” hg no matter what I manually restrict the starting vacuum to. I assumed a defective VCV and retrieved one from my donor vehicle and it yielded the same results. Two parts giving the same results seems odd to me.

Any thoughts?

My vacuum diagram is the same as post #42, page 3.

Thanks

If your transmission shifts OK I wouldn't worry about it. Mine goes down under 5" Hg at full throttle but I can't determine how much because the Mityvac's calibration ends at 5. I need a better gauge, I guess. It's possible that turning the boost up might bring the vacuum down but I wouldn't do that (adjust the boost) just to make the transmission vacuum signal lower. Your engine can't use much more than 11-13 psi of boost anyway.

Jeremy

Thanks for the reply Jeremy.. Unfortunately my system doesn’t utilize a transducer…I’d probably be better off in the long run to find a system like yours at the bone yard and install it on mine, but until then I should (hopefully) be able find a happy medium with the current setup.

I am having a shifting problem and was starting with the VCV as a beginning point. I guess I am having some ‘wishful thinking’ that I can solve my problem at the VCV.

Chris

If it doesn't flare on full throttle shifts, you've got nothing to worry about.

It does....:(..and part throttle shifts too.

Actually by removing the dashpot, the shifting has improved, but it's still not right.

How about a full description of the symptoms? The only thing you've provided to date is the fact that it won't go below 5" vacuum.

Provide exactly what it does on various pedal positions and various rpm points.

Have you measured vacuum to the modulator at idle?

Any monitoring of vacuum during various part throttle tests?

I’ve read the posts on other problems and didn’t want to beat the ‘dead horse’ here with all my symptoms, but since you asked….:D

Short shift on 1-2 at anything but WOT.
Flare on 2-3-4 any RPM range, any speed----not so much at WOT, but still present
No downshifts except when ‘kick down’ switch under pedal is depressed.

15” hg at modulator @ idle (tested--holds vacuum)

No drive/monitoring Hg tests yet—just starting diagnosis.

Throttle linkage is correct and I am getting full range of travel on the VCV. I also tested both VCV’s with the linkage disconnected and operating the valves manually with the engine idling. Both valves operated smoothly through the range and would only go down to 5” Hg. I used a pair of self-locking hose pinch pliers to restrict the supply vacuum to 8” Hg (as mentioned in your posts as a good starting point), still only 5” Hg at full travel. VCV's bench test good as per directions posted in thread.

I’ve had several vacuum issues with the car that I have been slowly working on and have now corrected and I am starting to work on the shift issues, before I cook the trans.

I am pretty sure I don’t have a major internal trans problem as through the course of fixing the vac. leaks, the trans would shift fine (or close enough) until I fixed another leak or two. As I tighten the vac system up, trans shifting became increasingly worse. I also drove to work once without any vac to the modulator. I squawked the tires on every shift,any rpm (no flare) and my neck is still sore.:)

I know it’s capable of shifting correctly; it’s just a matter of where I start to look and 5” hg at WOT didn’t seem correct to me from what I've read.

Thanks,
Chris

That vacuum level should be reduced to about 8-9". On the '84, there is a small domed cover on the side of the VCV. There is a tiny slotted screw that makes the adjustment under the cover. The movement of the screw will only be about five degrees...........don't go more. Adjust the level at idle down to 8" and see how it drives. You can use the Mityvac with the engine not running. The VCV will bleed all vacuum above the setpoint.

Thanks, I’ll do that tomorrow.

Right now with the dashpot removed from the system it is shifting correctly and firm at all RPM’s which is what I prefer. Only a barely detectable flare on occasion, but no downshifts still. I’ll see what I get after the VCV adjustment.

Thanks again,
Chris