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:
http://www.peachparts.com/shopforum/showthread.php?t=160169
and more specifically at POST #5 :
http://www.peachparts.com/shopforum/showpost.php?p=1247118&postcount=5
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,

I broke this plastic tee today trying to get the hose off to take a vacuum reading. I started the engine but it won't shut off. I pushed the broken tee to seal and the engine shut off. Not knowing what other problems this will cause I got creative. I tapped the broken tee with a 1/4 -20 tap (after drilling out with tap drill). I machined a nylon adapter on a lathe with 1/4-20 die and threaded it in the newly tapped tee and connected the hose and all's back to normal.

I want to see if I can make the transmission shift better. It flares sometimes starting from a standstill and jerks forward. It also makes a pronounced clunk coming to a stop. Are these signs of vacuum problems to the transmission vac modulator?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

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

(1) Extra Ordinary Fixes - IF you are inclined to perform such intricate work on these brittle plastic T(s) in the Pump-to-Brake booster chamber... I would recommend you fashion a metal "T" in this, the main vacuum supply line.
(2) Tweaking the Engine/Tranny Vacuum Control System - Yep, this is why this THREAD was started by me more than 250 posts ago. For those of us on this THREAD to help ya, we need for you to go through a series of vacuum tests and report to us the results. I trust you have a vacuum hand pump/gauge... the tests include:
(a) tell us what year and model diesel you have,
(b) go to the website : http://www.peterschmid.com
(c) and then their webpage: http://www.peterschmid.com/vacuum.htm
(d) follow thru the menu structure and find the appropriate vacuum diagram for your year/model/engine car.
(e) report back to us with all of the above.
Regards,

I wouldn't call that intricate work. It was done in less than 1/2 hour and done out of necessity because it was broken. That's a great idea to make it out of metal so it will not break again. Is that just a plain tee or an orifice that I broke?

I will go through the procedure you outlined and report back. I do have a Mighty Vac. Thanks for the guidance.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Funole,
A1 - I think most of the "T"(s) are also restricted orifices... that's why we need to try and find the proper vacuum diagram which will tell you [most of the time]. But even if it's not, you can put an in-line restricted orifice in the line just as MBZ did when they "tweaked" these cars as they came off the assembly line [IMHO]... or at least that's my explanation of their use of so many restricted orifices... orifices here and orifices there. I say that these were originally to do two things: (a) balance the vacuum to each specific vacuum using/powered component [as needed], and (b) to conserve vacuum for where it is absolutely needed... the vacuum assisted power brakes. I also think the later model cars went to a separate electric powered vacuum generated just for the door-lock, fuel door, and trunk-lock systems... they did this [IMHO] just to get away from possible lawsuits from the brakes being starved for vacuum when a door-lock diaphragm ruptured or a vacuum line pulled loose!
Regards,

The T's in my 1982 booster line were open (large holes).
The T's in my 1983 booster line were restricted.
When I ordered replacements, both lines sent had T's with the larger holes.

The only reason for having orifices of smaller size in the T's would be to increase vacuum to the brake booster, but as long as your system is tight enough to maintain ~25" to the booster, all is well.

__________________
1982 300CD Petrol/Black Leather

1983/300CD,
One way or the other, the restrictions are needed... unless your vacuum pump is wearing out!

I have gauged the I.D. of some of several of these "T"(s) on the main vacuum line and found most to be ~0.8mm. IMHO I would equate "open" to be ~ 2mm or larger which is the opening in the largest of the MBZ in-line orifices... thus also IMHO, IF new replacement main vacuum lines come with "T"(s) that 2mm or larger openings, I believe it would be necessary to use in-line orifices that are 0.9mm or smaller to reduced the "strength" of the vacuum such that you would be able to properly adjust the vacuum on cars with a vacuum control valves [VCV] mounted on top of the Injection Pump (IP). Otherwise you would NOT be able to properly adjust the VCV so that the tranny's modulator valve would see the proper varying vacuum signal simulating changing throttle.

I agree that restricted orifices [whether in the main line "T"(s) or in-line orifices]... these are there to help "conserve" vacuum for the brake system, but IMHO these restrictions are also there to provide a final degree of "tweak" or control of the vacuum being supplied to the various vacuum using components... for example EGR, VDC, modulating valve etc.

So IMHO you either have to restrict the vacuum at the main line or bother there and later with in-line restriction(s). One of the diagrams on the www.PeterSchmid.Com WebSite actually gives you the sizes of the 6 or so color coded in-line orifices!
Check out: http://www.peterschmid.com/vacuum/1977_1985/617_95/1981_1984.jpg
Regards,

The 1982 was all original when I bought it (including booster line), and it had larger openings. My black after-VCV line reads 10" at idle and reduces to 0. Remember, it still has the orifice in-line before the Y connection leading to the top of the VCV.

__________________
1982 300CD Petrol/Black Leather

That's tongue in cheek.

If the output from the vacuum pump dropped to sufficiently low levels (pump failing), the vacuum system wouldn't need the restrictions to keep airflow levels within specifications.

Naturally, you'd have no brakes at that point...............

1983/300CD,
There has been talk on this FORUM about how one can drill out the "T"(s) in line between the main vacuum pump-to-booster chamber. I suspect this is most often done because the OEM restricted orifice "T"(s) do become clogged with dirt over time and instead of just cleaning them out with solvent and/or a piece of wire, many DIYers have just drilled them out with any bit they could get fit into the "T" !. As a retired Certified Safety Professional [CSP...not Prof. "PE" ], this is where I have taken issue by issuing CAUTION, CAUTION, after CAUTION by appealing to logic and reason. IMHO logic impells me to try and understand WHY these systems were designed the way they were. I also advocate installation of clear in-line air or fuel filters at the appropriate locations under the hood and under the dash to try and keep dirt out of the vacuum systems plumbing and in the case of the IP shut-off device line where it is in plain view under the hood, such a filter acts as a visual "tell-tale" to warn that the shut-off device is failing. The really BLACK engine oil of these diesels really stands out when sucked into filter on its way the ignition switch, eventually to drip on the pantsleg of driver's best slacks!
But I digress a bit didn't I.
Regards,

Holy crap Batman the transmission is shifting smoothly now! OK, I have an 83 300D turbo. I believe the vacuum diagram posted by Brain Carlton on page 2 of this thread represents my car. I pulled the hardline to the transmission modulator and noticed it was a little loose. Put a Mighty Vac on that line and it holds vacuum! Good start, the transmission modulator is good!. I pulled off the rubber T's and noted they were loose and oily. I washed the grease off and trimmed a little of the ends of the T's that are loose. I also noted the hard line to the VCV brass fitting was slightly bent and may be leaking. I didn't want to pull it off for fear of breaking it so I put a piece of duct tape around it temporarily. Put the T's back and went for a test drive and it felt like a different car. It now shifts up or down with no more banging of the gears. It is also shifting at different RPM's than before. So this thing I've read on the web that the 80's Mercedes transmissions are suppose to shift hard with an authoritative bang is apparently a lot of horse *****?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Brian,

I studied the vacuum lines to the black box on top of the valve cover and it does appear that it only control the EGR valve. I am puzzled why this DIY procedure at Dieselgiant http://dieselgiant.com/trannyleverreplace.htm specifically states that replacing the worn vacuum levers will fix transmission shifting problems?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The vacuum levers leak. Russell advocates replacing those levers so they don't leak. He sells the levers. He really cannot advocate removing the EGR levers completely.