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Mercedes 300D Suggestions



  • Okay, I'm back. I'm now wondering if the starter lockout/backup light switch might be defective since I've been told that my backup lights don't work in addition to the car not starting in Park. Is this switch activated by something internal in the transmission or by something external in the linkage?
  • dotish.... this problem is one I am not familiar with, however, if I were faced with the situation I would make sure the key was not in the ignition when you open the hood as , as you said the battery goes dead and that ticking could represent the battery's last gasp so to speak because of the key alarm, open door alarm or open trunk alarm( buzzers and lights). With that cleared uo, next perhaps the radio is not operated by the key, and again the battery's last gasp. Third, if you boost the car to start it, when you turn it off, be sure it is either dark outside or park the car in the garage, turn motor off, close garage door, turn off garage lights and see if there is any light inside or outside of the car, that would represent a closed circuit to some light source that should be open as the ignition switch is off, doors and trunk closed, and light switch off. Check your cigarette lighters and ash tray lights, glove box lights, switches for rear window defroster, emergency brake light, vanity mirror lights, seat warmer light. Make sure top of battery is clean and no corrison at terminals. Also, the disk brake sensing light may be defective or loose and draining the system. Let me know if this helps and happy hunting. benzsilver :shades:
  • burdawgburdawg Posts: 1,521
    That "vacuum distributor" sounds like the servo valve to me, which is part of the climate control. It's also is electrical, so it could be the problem...............
    Does it have a large block of vacuum lines, electrical connectors, and coolant hoses going into the bottom? If so, it's the servo valve.
    The way I have always trouble-shot electrical drain issues is to disconnect the battery and put an ohm meter across the battery cables. Disconnect any lights, etc that could be activated (such as an underhood light) and then see what the resistance is across the cables. It should be very high. If not, then start disconnecting circuits by removing fuses until you find one that causes a big change. That will at least point you in the right direction. Some fuses are in line and may be more difficult to find. A good wiring diagram helps immensely.
  • Thanks for your reply. Yes, it's definitely the servo valve and it's definitely what's ticking when the battery is connected and nothing's turned on, including the ignition. If all that the servo does is related to climate control, I'll just disconnect it, since nothing except the defroster works anyway and I'm not going to need that any time soon in Texas.
    Thanks for the battery drain troubleshooting tips.
  • my 84 turbo deisel benz runs fine but wont go forward or backwards-It is an automatic.what could be the problem.It stopped moving after i shifted it in reverse after going forward without completely stopping
  • Any thoughts on how best to find a potential new owner (preferably in Bethesda, MD) of a classic '84 300D in need of some fix-ups?
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,413
    Craigslist is really the best venue for this type of car. You want dreamers---big dreamers.


  • benzsilverbenzsilver Posts: 21
    edited January 2011
    '84 cdt won't stop running when key is turned off! Help
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,413
    edited January 2011
    It sounds like you have a defective vacuum shut-off valve for the fuel. This is located at the left rear of your engine (driver's side is left).



  • Mr Shiftright: Thank you for your response. While checking the location of the shut-off valve, I have discovered a black vacuum line that goes thru the fire wall along with two yellow lines a green line, two gold blue strippped lines and another line. The goldblue stripped lines are connected to the ignition switch, the yellow lines go tward the defroster ducts, the green toward the a/c system and the other line somewhere else. these are all connected to something; however the black line is not connected to anything under the dash inside the car. the other end is connected to the y- connector that connects to the big line that goes to the booster and the business that sits on top of the rocker arm cover. I have looked for vacuun diagrams, however, none that I have seen so far illustrate the line that I am seeking a connection point. My vehicle is a "84 300 CDT. I have removed the lower dash panel and instrument cluster to be able to see the area better. I would appreciate your help and info regarding this quest. benzsilver and thank you again :cry:
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,413
    I don't have such a diagram either. Best thing I always suggest with loose vacuum lines is to extend them as far as they will reach in a 360 circle until it meets up with a connector that it can reach.


  • Glad to see Mercedes-Benz recognizing the work of Mercedes Motoring out of Los Angeles. They do some incredible work. I've followed them for years and their restorations only get better. Check out this short documentary on
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,413
    Too bad the people making the video were more interested in their cameras and the music than in actual content. :mad:


  • Hi Everyone,

    I'm thinking of selling my 81 - 300D non turbo sedan with automatic trans. I do not want to mis represent the car so would you please comment on my following statement about the transmission.

    Bought it in Houston 4.5 years ago and have been using it down here in Cuernavaca, Mexico ever since and it stills runs great at 220,051 miles, which I believe to be accurate.

    I noticed when I bought it that it ran up higher rpm's before shifting than I was accustomed to. A non related mechanic of vintage Mercedes' told me it was designed that way to keep the small diesel at high rpm's when climbing hills or steep mountains.

    I thought it made sense and I went back and bought it. But I did think it strange, and still do, that it would not shift earlier without a load on it.

    My 79 300 SL turbo., which i believe had a little more powerful 5- cyl. engine always shifted like the many american gas cars I've owned over a lifetime.

    The little 5 banger has faithfully climbed Mexico's highest mountains and has made countless trips between South Mexico and Texas and Louisiana. The trans. shifts the same today as when I bought it. A different Vintage MBZ mechanic in Dallas told me the same thing plus gave me a tip to release the excelerater momentarily when I wanted it to shift earlier and that has worked fine over these 4.5 years.

    Can any of you pros. out there tell me the correct story of this particular automatic tranny?


    PS: I'm fairly certain the Trans. is operated by vacuum from a vacuum pump attached to the engine.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,413
    Sounds pretty normal to me. You might check the vacuum lines that go to the vacuum modulator---or check the vacuum lines in general. If you have any kind of vacuum leak, this will affect how the transmission shifts.

    One tip off of a large vacuum leak would be that you can shut the engine off with the key sometimes.


  • Thanks for your opinion Mr. Shiftright.

    Mickey Patin
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,413
    By all means check the small vacuum lines and junction blocks that sit near the top/back of the engine on the driver's side.


  • dotishdotish Posts: 20
    Hi, I've just purchased a 1985 300D turbo that runs well, but shifts with a jolt into 2nd gear. Can anyone suggest what the problem might be? Vacuum leak?
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,413
    Sounds just like a 300D to me! :P If it was a vacuum leak, it probably wouldn't shift at all.

    They shift hard as a rule. Of course, we can't tell what you mean by "hard"---compared to modern transmissions or compared to other 300Ds?

    These are wonderful cars, but cars have come a long way since 1985, and now transmissions are electronically controlled to the max.


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