It sure is amazing how many variations in shifts we can manage to come up with! I don't think I could ever get my 3-4 shift to occur at 3000rpm unless I was at full throttle.

__________________
2009 VW TDI Jetta Sportwagon 172k miles (rear-ended harder than Elton John on 8/4/13. Total loss)

1991 Volvo 240 142k miles (T-boned by a stop sign runner. Total loss)

It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...

Incorrect vacuum to the transmission will cause differential wear over time. This is what occurs after years of no vacuum and hard shifts.

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Thanks for the input for this is a somewhat different slant on this subject of setting up the vacuum shifting systems for these AutoTrannies!
Regards

I was just getting caught up on this thread and read with interest this item about incorrect vacuum to the tranny causing differential wear over time. I purchased a mityvac and now that the weather is getting better and I have my benz out of the garage, I need to get my hard 1-2 shift problem solved. I replaced a few cracked vacuum hoses last fall and closed off the EGR system, which improved the 2-3 shift and softened the 1-2 shift.

But now to the point of my post: I have this rumbling that I feel when slowing down to an idle, and have assumed that I need to look at the univeral joint. But maybe it is the differential. If my problem is the differential, is it something that can "bust" suddenly and leave me standed, maybe doing further damage? I have never worked on a rear end. How involved is it to inspect the differential gear and replace it?

__________________
85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

RML - First off I confuse parts terms and confuse differential & universal all the time ! Take a look in your PM.

Yes, I think your "rumbling" probably is in the drive-line... and is in order of likelihood either:
(1) so many miles and wear-and-tear on your car that the differential[rear-end] is getting loose! A good way to diagnose this is to drain the oil and put in the heavier 140 weight gear oil. If this quiets things down some, you know you have found the problem... and you might want to keep the heay lubricant... realizing it will knock a little off your fuel mileage!,
(2) one or both of the two flex couplings in your drive line,
(3) one of your drive CV axles,
(4) the center support bearing and/or rubber mounting for this bearing, AND/OR
(5) also check the rubber support(s) that the differential hangs from or is supported by.
Regards,

Hello all. One month ago I bought a 1982 300D Turbo off a local used car lot, looking for a car I could (a) maintain myself and (b) eventually convert to run on waste vegetable oil. Body and interior immaculate, new Michelins. On test drive, noticed what I thought was "slipping" between 1-2 and 2-3 gears, but since the price was so good, thought I'd take a chance.

Began browsing the web, found DieselGiant, then Shopforum. Read extensively, bought about $100.00 worth of vacuum components, then began. And here's what happened.

With vacuum valve, checked Hg at brake booster, ~22" Hg, then checked components downstream. System would not hold vacuum. DieselGiant recommended checking master vacuum switch, found it to be good. Traced vacuum lines from master vacuum switch in driver door, found that at some point the yellow/red and yellow/green lines had been crossed, straightened that out. Found leaky actuators (driver's side rear door, trunk), replaced the former through Ebay ($25.00), latter removed and lines plugged. Pulled vacuum at master vacuum switch, all locks worked as advertised. Pulled vacuum at dual connector off principal vacuum line (one goes to master vacuum switch, other to vacuum reservoir), all locks worked. Cranked her up, door locks don't work. Test drove, transmission as before.

Came here. Found vacuum schematics (first BIG thank you), noticed valve in dash. Checked valve in dash after removing instrument panel, found valve installed backwards. Reversed valve. Checked vacuum at dual connector off principal vacuum line, door locks worked as advertised. Test drove, transmission as before.

Began serious work in engine compartment. Following DieselGiant, checked ALDA connections, found the lines to the ALDA switchover valve (on firewall next to brake booster) were disconnected from the valve and connected together. Reconnected to switchover valve. Removed and cleaned banjo bolt, reconnected. Test drove. Door locks worked as advertised (an indication of good system vacuum integrity), transmission as before.

Returned to engine compartment, read more on Shopforum, this thread, and discovered vacuum control valve (VCV). Tested vacuum, found it to be solid 14" Hg from the top connector. Test drove. Transmission as before. Went back to VCV, noticed for the first time that the rocker arm from the throttle linkage was disconnected from the metal lever on the back of the VCV. Which means my transmission was getting solid 14" Hg through all shifts (no wonder the "flaring," a more precise term, I have learned, than "slipping"). Reconnected rocker arm, which turned out to be frustrating because mine has a loose plastic clip to hold the rocker arm onto the metal lever on the VCV. Tested vacuum bleed from top connector, went smoothly (whew!) down from 14" to 0". Just for kicks, checked vacuum on line to transmission, found it to be solid. Test drove. No flares, though shifting was extremely soft (i.e., slight flare-like shifting between gears) and shifting occurred around 3200 RPM.

Following DieselGiant, replaced transmission vacuum valve levers (old ones were worn significantly), commonly referred to as 3/2 valves. Test drove. Still soft shifting and high RPM.

Came back, read more Shopforum. Learned about the control pressure cable (I believe it's referred to as a "Bowden" cable, obviously named so by a Florida State fan), adjusted it as per decription elsewhere here on Shopforum. Then read about vacuum adjustment on VCV. Removed plastic dome, adjusted nut (not screw) until vacuum ranged from 10" Hg down to 0". Test drove. NO NEED FOR A NEW TRANSMISSION. Shifting was extremely crisp (my tires tend to squawk a little between first and second, unless driving upgrade) and all gears shift dead-on 2300 RMP. And all of this with the EGR still connected.

Tonight, I adjusted VCV to 12" Hg initial vacuum to see if tomorrow the 1-2 shift is a little less harsh while not leading to minor flaring between 2-3. Again, big thanks to this forum, I do not need a new transmission.

Here's some learnings and questions I still have.

1. After all this, my cruise control began to work whereas it didn't before. Does the cruise control depend on a tight vacuum system?
2. Adjusting the control pressure cable: I tightened the cable to remove noticeable slack (right at the point of feeling resistance to the pull) at the point the metal connector was at rest, not against the metal stop between it and the cable bracket. The gap was around .15". Perhaps this is peculiar to my car, but by maintaining that at-rest gap I was able to fine tune shifts to current RPM.
3. One could, if one wanted an extreme exercise in frustration, adjust non-adjusting VCV by changing the height of the rocker arm connection to the throttle system. I imagine that would entail significant trial and error, since one would have to identify the exact point at which vacuum begins to bleed, then adjusting the rocker arm at-rest to connect the lever on the VCV at slightly before that point. Ugh. However, I'd bet that's what the designers intended, since different VCVs may begin to bleed off vacuum at different lever positions.
4. BTW, that flimsy plastic connector that ensures the rocker arm will stay on the lever on the VCV: I intend to replace it with a spring-lock, since the tip of the rocker arm has a groove around it. I was driving two days ago and the rocker arm slipped off - back to flaring between shifts.
5. Sam, regarding the orifice openings: I'm sure you're right, though I'm a newbie to MB's and am speaking as a rank amateur, that the orifices are fine tuning methods for delivering precise vacuum to the different components while ensuring that the brake booster always receives sufficient vacuum. That being said, I would not mess with them unless, for instance, I could not get sufficient vacuum at the VCV to reach my starting point of vacuum (formerly 14", then 10", now 12" Hg). I would love for a more physics-minded reader to give an description of how much a particular orifice size restricts vacuum, for instance, how much a .8 mm orifice restricts 22" Hg.

So, that's my story and I'm sticking to it. Again, huge thanks to this forum, particularly Brian and Sam. Though I still have some things to do (fuel low light always on, plastic door buffers in locking mechanism rotted), most are minor compared to my worries over the transmission.

__________________
Rev. Jeff Hayes
New owner, 1982 300D Turbo, 214,000 miles

"Reverend?" Jeff,
Wheeew! [sp?]… you were sure not at a loss for words!! Are you a Preacher or Priest? You included enough for three separate THREADS all in one POST! A bit of tongue-and-cheek advice – in the future think of these THREADS and the POSTS in each THREAD as being part of a huge technical database that will be archived and then in the future someone will be SEARCHING and seeking specific help on a technical problem [ just as you did ]… so it’s probably best for future readers IF we try to keep our POSTS in each THREAD consistent with the very first subject line of the THREAD… a subject line that it appears even the original author canNOT change. MOST of your POST falls into two different categories: (1) Engine/Transmission vacuum system, and (2) Door Lock vacuum system. This THREAD was intended to address the Engine/Transmission Vacuum.

Now that I have chided you, let me also compliment you for your dogged determination to solve your vacuum problems and your capacity to deal with so many different things that were wrong on your car in these vacuum systems.

I thank you for your compliments and recognition for myself and Brian in your POST. Such courtesy and civility is often overlooked by many of us who have become too familiar with one another here on the FORUM.

Regarding the subject of Door Lock Vacuum Control systems on W123 chassis cars, just in case you missed it, take a look at this THREAD:
W123 Vacuum InterLock Diagram
and more specifically at POST #5 :
W123 Vacuum InterLock Diagram
where you will find 3 links to space on a WebSite donated by someone I met on this FORUM… links to two different file formats of a color diagram for the W123 Vacuum System for the Door Lock System [ a good future reference to print and share with others ]:
http://ericandkat.com/mercedes/W123VacDoorLockDiag.doc
http://ericandkat.com/mercedes/W123VacDoorLockDiag.WMF
and another link to a photo showing how to use small electric wire ties to salvage many of the loose/leaking rubber vacuum connectors:
http://ericandkat.com/mercedes/W123VacDoorLockDiag.JPG

Welcome to the FORUM "Rev" and please try NOT to write your POSTs on Sunday!!
Regards,

If you turn that clip on the linkage rod, it functions quite nicely.


As for the orifices, have you ever tried to set up a fish tank? If you have too much hose on one side of a splitter, you will get just about all your pressure through one (the shorter) hose. If you would put an orifice on the shorter line, you can force air flow from both. Same idea, but reversed.

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1982 300CD Petrol/Black Leather

Hey fellers -- just to add to the confusion, I have a 1980 Euro 300D. No EGR, thus a very different 3-2 valve arrangement (just one valve, so I'm not real sure what you'd even call it). Three lines go to this valve arrangement, and one of them goes straight to the transmission, with no little green dashpot that I can find. My transmission flares and shifts early, and I'm not really sure where to start, even. I do have a MightVac. Anyone mind taking a look at some pics if I can shoot a couple? Thanks in advance!

__________________
1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)

Despite the fact your 1980 300D is a Euro model, maybe we can help you out... but first we need some further clarifications:

Q1 - Have you looked at what I believe is going to be the closest "Engine/tranny" vacuum diagram we are likely to readily find... the diagram at: http://www.peterschmid.com/vacuum.htm: and then: http://www.peterschmid.com/vacuum/1980/617_912.jpg ?

Looking at this diagram, identify for us each of the numbered vacuum components that you actually have on your 80' model 300D Euro MBz... e.g. I believe what you call the 3/2 valve is shown on this diagram as #64 and called a "Switchover Valve" and is on top of your valve/cam cover. PLEASE identify [from this same diagram] every component that you have... by #___ & "name" as shown in the diagram. We need this supplemental information for we could spin a lot of wheels [not to mention minds] needlessly.

While you look at this diagram, also NOTE #63 a small "orifice" and #62 a plastic Tee also shown as an "orifice". IF you have read the earlier POSTS on this somewhat lengthy THREAD, you will know that I'm big on the subject of these restricted orifices which I believe were MBZ's way of doing the final tuning of the vacuum control systems on these vintage diesels that had automatic trannies.

Q2 - You did indicate "flares" which usually means you must have an auto tranny!??

Yes, I will take a look at any pictures but please first go through the I.D. drill I have requested above.

A final question that should be included in the above I.D. drill:

Q3 - Are you telling us you do not have a vacuum control valve [VCV] which is incorrectly shown as a "vacuum modulating valve"?

Yes, you will see some of these vintage cars' vacuum components with names that are NOT what we in the U.S. know them as!!
Regards,

Thanks for the reply, Sam. To answer your questions:

1. Yes, I looked at those diagrams, and the print is too fine on my laptop to read. When I save it to desktop and try to increase it, the font is just blurry. I'll post pics of what I have, but there is *no* EGR, and what appears to be the 3/2 vavle on other engines (the two valves on top of the valve cover, under a black plastic cover) consist on ONE valve on my car. I took a pic of this. The line coming off from the far side, making a "U" back toward the driver's side of the engine compartment, appears to be the line to the tranny. The two going into the "switchover valve" from the driver's side run down to the IP. There is no green dashpot in it that I can see. Yes, I did see your comments on the orifices and suggestions against drilling them out; the car is new to me so I cannot speculate on whether or not that (or anything else) has been done to it.

2. Yes, automatic transmission, of course.

3. Yes, if I understand correctly, the VCV is the green dashpot, correct? I see none.

Thanks again!

Chris

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__________________
1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)

Chris,
I have been assuming your Euro 300D is the smaller W123 chassis, NOT either a W116 or W126 model, both which would be the equivalent of our 300SD models. So:
Q1a - Which is yours?
Q1b - Does your engine have a turbocharger?

As to your 3/2 valve... I looked around and the triple-connection vacuum switchover valve you show is what I know and see at parts WebSites as a "3/2 valve". Only the 1980 W126 300SD models have a double [2 separate] valves arrangement. Seeing all three of your connections on your 3/2 valve in use is a bit unusual for our 1980 300Ds and 240Ds that are both W123 chassis only use two of these and this is born out by the diagrams you are having trouble seeing and/or reading.

Your center photo shows what appears to be a VCV [a VCV is not the same as a dashpot ]... well this photo raises more questions than gives answers. First, the 1980(s) models W123 chassis delivered in the U.S. did NOT have a green dashpot at all so don't worry for now about there not being one there. What I see as possibly a strangely located VCV, this device has a " Y-shaped " vacuum connector on top of it and I must assume that the black w/green striped vacuum line that comes down from above to one side of the " Y " comes from the 3/2 valve up above.
Q2 - Where does the 2nd vacuum line go that is connected to other [right side in photo] branch of this " Y " connector?

Q3 - Why don't you try a little "Simple Green" or other degreaser spray solvent and then wash off some of the "GUCK" !?

For future reference, it appears to me that your IP [injection pump] appears to be a " MRSF " type ... and it appears that just maybe you have a vacuum line attached to your " ALDA " on top of the IP

Hi Sam -- yes, my new car is a 1980 300D (thus W123 and normally aspirated). Sorry for the lack of detail! Yes, the green/black line goes to the valve. The other line you see coming from the "Y" that the green/black line shares runs up to another junction, which is visible in the last pic. It's the line running up just in front of the filter housing in the pic. You can see that it attaches to a connector that is fed by the main line from the vacuum pump, and also feeds the lines that run through the firewall (door locks and whatnot, I presume).

As for the gunk... I just got the car Friday morning, about 5 minutes before I left for work. I was gone all day Friday and again all day today, and it's near freezing to boot... so I have yet to wash the car at all, let alone detail the engine! Sorry for the dirt and grime in the pics; I know it doesn't help identifying details! Tomorrow I'll take a better pic of the lines near the ALDA/IP. It's certainly different than any other arrangement I have seen, I believe!

Thanks again,

Chris

__________________
1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)

I now believe that what I thought was an ALDA on top of your IP is probably the IP's round vacuum actuated IP/engine shut-down device... and the vacuum line that leads to this device comes through the firewall from the ignition switch.

I have also made out what looks like a restricted orifice between the " Y " connector and what I believe is your VCV on the left side of the IP [ an unusual location for VCVs].

Regards,

Chris/cscmc1,
Q1 - Is this the same car we are talking about?:
http://cgi.ebay.com/ebaymotors/Mercedes-Benz-300-Series-Mercedes-300-1984-Mercedes-Benz-300D-Magnificiently-Priced_W0QQcmdZViewItemQQcategoryZ6330QQihZ013QQitemZ230113670135QQrdZ1QQsspagenameZWDVW

Q2 - IF you answer yes to Q1, do you think it really has a new tranny?

As a "Euro" car, we might have some difficulties working out this engine/tranny vacuum control system. I believe you will not only have to do a lot of cleaning, but because it is a "Euro" you should really document thoroughly with "pics" anything that you have to take apart for cleaning... this way you can use your photos to put things back... all the while realizing that something might not be correctly assembled as it is!

I'm particularly interested in what I'm all but positive is a Vacuum Control Valve [VCV... aka vacuum modulator valve in some diagrams] that is mounted on the left side of the IP. If this was my car, I would start [one at a time] start removing just such vacuum components to clean them thoroughly and pick off any P/N(s) I could find. Such info might just prove invaluable. I know proper functioning of this VCV is critical to the tranny's shifting and so IF the tranny is "new", then you might try to find out who did the replacement!

What is really puzzeling is that I have access to some old "MBZ of N. America" shop manuals that show this exact VCV and it appears to be on a 617.91 series engine. I see you have been shopping around for such a diesel for some time... can you confirm for us the VIN and other specs for this car? So you might luck out and find many of the parts on these "Euro" models are the same as on U.S. delivered cars... let's hope so!

Regards,