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Old 05-28-2005, 11:32 PM   #1
pbc_godfather
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78 300D W123 vacuum and tranny help

Can someone please explain to me what exactly should go to my automatic transmission in terms of vacuum and electrical lines? I read things about modulator valves, vacuum valves etc. The problems I am having with this car seem to be the typical: tranny slipping between shifts (I think the term is "flaring"), engine won't shut off when you turn the key. This is how I bought the car and its vacuum lines are a mess. For now I don't care about power locks or any other vacuum driven options. I just want to be able to shut off the engine from the inside of the car. Also what are those vacuum lines (at least that's what they look to me) going from injector to injector? I have replaced the vacuum pump diaphragm so there should be sufficient vacuum. The main line going to the brake booster was broken and somebody did some "custom work" there connecting the lines. Is there supposed to be a big check valve in between? Sorry, didn't mean to write a whole essay. Can't find a manual for it either so that's a problem. Finally got a job that is up to my education but it is somewhat inadequate to open the hood each morning and shut off the engine on the parking lot. On the other hand I don't want to get rid of this interesting car. First diesel I own and have to say I am quite impressed.
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Old 05-29-2005, 11:33 PM   #2
talonlover
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I will try to help with some of the small stuff, the engine shut off is most likely a shut off switch, which is a small vacum diaphram located on the injection pump. Look at about 50 dollars for a new one, but easy to replace. The "vacum lines" between your injectors are your loop lines, these are diesl lines, unless they are wet or leaking, don't replace them, but if they are, it's also a easy fix and will cost you around 15 dollars for the line. I would say that a lot of your problems will correct themselves(maybe even your engine shut off) when you replace your brake booster line. This would be my very first thing I replace if I were you, it's cheap too, about 25-35 dollars. There are indeed check valves on most of these lines and it is very easy to get the vacum lines screwed up, but when one of these things leaks it's almost impossible to repair them with glue, tape, or sealer. Also when this line leaks it plays havoc with just about everything vacum related, including your transmission and brakes. I don't want to say your transmission will be fixed by replacing this, but it wouldn't suprise me if just about all of your problems you listed were related to this one thing.
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Old 05-30-2005, 04:28 PM   #3
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Thanks for educating me! This is exactly what I will do. I will replace the booster vac line and go from there. A Haynes manual is on order so hopefully it will include an accurate vacuum diagram. I don't know if this car is missing some stuff (I would not be surprised) but I don't have a change over valve on the valve cover and I don't see any vacuum lines going to my transmission. About those diesel loop lines - it starts from the top of the fuel filter, then goes to the injectors and it ends at the last injector. A little strange to end like that I think but maybe this is correct. Anyways, I will stop by the dealer to see what I can get.
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1966 MB 230S Euro - a classic European: high RPMs, 4-sp manual, no AC, no radio, no nothing!

1972 MB 280SE 4.5 - beautiful interior with red seats, purple dash, sun absorbing wood grain. A timeless machine with power to spare if you can tolerate that fuel consumption - I can't!

1978 MB 300D - driving the previous car on the list, resulted in the purchase of this one. Still have mixed feelings about it but I like the engine.
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Old 06-08-2005, 01:58 PM   #4
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Cool

Hey There
Still Having Car Trouble???
That Fuel Line Your Talking About Is The Fuel Return Line And Just Presses On..you Do Need To Buy It From The Dealer So As To Avoid Leaks..no It Doesn't Use Tiny Little Hose Clamps Or Anything Else The Hose Is Made To Seal By Just Being Pressed On.
Check Your Tranny Fluid Level--
1 Turn It On And Let It Warm Up
2 Hold The Brake And Shift Slowly Through The Gears Including Your Lower Drive Gears So As To Allow The Tranny Cooler And Torque Convertor To Fill Then Check The Level...
Also If Your Tranny Has Not Been Serviced That Would Be A Good Thing To Do..
For Your Shut-off Prob. Use A Vacuum Pump Or Suck On A Section Of Hose After You Unhook The Current Vac Line Off The Shut Off Valve At The Top Rear Of Your Injection Pump..by Manually Pulling A Vac Here While The Car Is On You May Be Able To Activate The Valve And Shut The Car Of And Also Narrow Down Your Prob..
These Babies Are Not Very Well Grounded..most The Electrical Systems Ground To Different Sections Of The Body Which Can Easily Rust Or Come Loose..also You Need To Run A Ground Wire From The Batt. To The Engine Block They Are Only Grounded To The Body Which Is Very Inefficient.
Good Luck
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