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Old 02-27-2004, 04:24 AM
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Join Date: Jan 2001
Location: North Carolina
Posts: 20
Question 300D Problems Any Ideas?

Several questions that I have not been able to find answers to. I used the search feature first as advised, yet I could not find threads that were close enough to my problems. I apologize in advance for any repetitive questions. These questions are all for 1981 300Dís. Please pardon the long thread. If you have time to read and respond, I would like to say thanks in advance for the effort.

1. Car 1 Dash lights are not dim; they are inoperable. The lights for battery, bright, turn signals etc work but the instrument illumination doesnít. I have replaced the appropriate light bulbs on the back of the cluster yet no luck. Any suggestions?

2. Car 1 This car is equipped with a vacuum lock system with which I am not familiar. I do not care about power locks yet the previous owner has done some tinkering with the vacuum system and the locks will not work even manually. If you push one down it will push the other up etc. Is there any way to disconnect the vacuum system and just have manual locks?

3. Car 1 The car will not automatically shift down when accelerating. The motor runs very well and will top out the gauge at 85, but it takes forever to get to 60 unless the trans is pulled to the S position. I think that it should shift anyway but it does not. Is this a vacuum issue as well or is this just the way these cars are?

4. Car 1 As stated earlier, the motor in the car runs very well yet it continues to run for about 1-2 seconds after the key is turned to the off position. Another vacuum system issue? Should I be worried? I do not want to get to the point that I am with the other car where it seems to run forever (See question 5).

4. Car 1 Radio works but antenna will not go up. I do not know if it is the motor or what. Is there a way to put the thing up manually?

5. Car 2 On one of the cars I bought in a pair the car continues to run after the switch is turned off. The kill switch under the hood does not work and the motor just seems to want to run forever. The car has to be turned off by sucking on a tube and shutting it off. As comical as it sounds, it works. How can I fix it so that the kill switch under the hood works? This is just a parts car that I eventually want to sell but I want to be able to turn the motor off.

The last question is just a matter of me trying to gauge whether my impulsive purchase was a mistake. As you can tell from the questions above, I just purchased a pair of 1981 non turbo 300D's. These are my first 123's. I purchased these cars to beat around town. I like the prospect of cars that seem to run so well yet are fairly inexpensive. I own several older Mercedes, a 126 coupe, 113 , and 108 (butchered with chevy 350) and drive a 129 as a company car. To make a long story short, I have several models but know nothing of the 123ís except that I like them. I was wondering if I paid too much. I thought I got a great deal (and therefore could not resist) at $900 for both and a Ford Econoline van full of parts (doors, trunk lids, lights, instrument clusters etc). Was this a decent deal for this bodystyle? Both had clear titles. One car runs and drives and even has new SLK wheels yet has no brakes and while the body is straight, the paint is not perfect and the interior leaves a lot to be desired. The second car looks good, interior and exterior. The dash is cracked and the trunk lid has slight rust but other than that, the car looks good. The second car also drives very well (drove it 120 miles at 80mph on interstate from sellers house) and has the minor problems, which I inquired about above. I am wondering whether it is worth the investment to sell one of the cars and try to build up the other. These cars are sooooo slow after the 126 (560 SEC) and the 129 (company car) but I love all Mercedes and one has a very nice ride. I feel like it would be dependable yet I am not familiar with the problems of these models. I would assume that since it is a Benz there will be only minor inconveniences butÖ.. Any opinions? Thanks Again for taking the time to read this thread.
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Old 02-27-2004, 07:14 AM
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Join Date: Sep 2001
Location: central Texas
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You made a good buy... most of your problems are vacuum related... you might want to consider finding a shop manual with the vacuum lines shown.... the 123's have a reputation for being easier to work on that most other models.... vacuum lines are tedious but you own a MityVac ?
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Old 02-27-2004, 08:30 AM
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Location: Metro Detroit, Michigan
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vacuum routing

Hello grey560
#2-3-4 sound like vacuum routing problems.
follow advice and sounds like good car.
Have a great day.
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Old 02-27-2004, 09:55 AM
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One try on #1, run a hard ground wire from the board ground on the back of the panel to a chassis ground behind the dash somewhere (leave enough loop to take the cluster in and out.)
1984 300D Turbo - 4-speed manual conversion, mid-level resto

1983 300D - parts car

1979 300TD Auto - Parts car.

1985 300D Auto - Wrecked/Parts.


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Old 02-27-2004, 10:13 AM
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For the second time this morning, I'll say that every W123 should come with a MityVac as standard equipment.

If you really don't want to mess with the vacuum door locks, lift the carpet out on both sides in the front, and look under the plastic channels. There you will find the vacuum lines joined by rubber connectors. Just pull all of them apart. Then go into the engine bay, pull the yellow vacuum lines out of their connectors, and plug the connectors (on the brake booster side) with golf tees.

The green vacuum line is for the climate control system, which could also be leaking.

For the dash lighting, pull the cluster out and check the rheostat. The springs are known to break, leaving you with no light. Some people just pull the rheostat altogether and wire the two posts together.

Somebody is sure to complain about the fact that I told you to destroy the lock system instead of fix it, which is relatively easy. But when I buy those cars from you, I'll put them back together properly.
Rick Miley
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Old 02-27-2004, 05:58 PM
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Location: Metro Detroit, Michigan
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make that every MB

Make that every MB and I would be in Violent Agreement with you.

The Mighty Vac is too handy to live without.
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Old 02-27-2004, 11:21 PM
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Location: Canton,Texas
Posts: 987
#2... the push the lock down others go up. Someone has got the vacuum lines backwards and they need to be switched (there are 3 lines). The "valve" is just below the lock inside the door panel so it needs to come off. One line pulls constant vacuum and the other two pull vacuum to either lock or unlock the other doors depending on the position of the drivers door lock. A mityvac or just sucking on the lines will tell you which one does what and you should be able to figure where to put them.

It's easy enough to fix the locks so I would just do it.... sounds like they all work.
1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k
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Old 03-02-2004, 12:42 AM
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Join Date: Feb 2004
Location: Berkeley, California
Posts: 214
I've just about finished troubleshooting my vacuum problems. ('80 300D)

Your tranny complaints may well be due to a disconnected line to a 'vacuum modulator' on the right side of your tranny. There's a hose that comes from a 3-way connection on top of your valve cover, it's black, and it runs down along/behind the driverside of the engine, to the right side of the trans. Check it out.

The 1-2 seconds between killing the ignition and the engine shutting down is a vacuum leak. There're two lines involved in the shutdown, brown and brown/blue I think. The both connect to the ignition switch... one comes from the main brake booster line, brown I think, and the other goes to the injection pump. They're obviously hooked up, but fittings may be leaking, or the lines may have a crack. I wouldn't worry about it. Maybe examine it to understand it, so that you'll have a jump on fixing it when it fails completely.

My antennae only works intermintantly, and I'm guessing it's a bad connection somewhere... ground, prolly. I'll be looking at it and my dash lights with that in mind (Thanks TomJ).

The kill switch on top of the valve cover should be connected to the injection pump (IP) with a mechanical linkage. Look at the one and troubleshoot the other.

Have fun!

Ash Peltier - tools, truck, tales
1982 240D - (272,000)
1998 Honda VTR1000F(RT) Superhawk Freeway (58,000) "Madrid"
1996 Toyota T100 4x4 (84,000) "Mary Kay"
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Old 03-04-2004, 12:48 AM
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Join Date: Jan 2001
Location: North Carolina
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OK. So I've bought a vacuum book and a mighty vac and I'm going to try to learn how to fix the locks. It looks like every problem that I have is related to the vacuum system so I guess I need to learn. I just wanted to say thanks for all of the replies. Thanks Again!!!
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Old 03-04-2004, 01:40 AM
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Ok you got the Mityvac.

2. Go here and read about the system on your car. Engine items will be a little differnet this is a 300D turbo yours are not

Open and print job numbers

80-010 thru 80-902 these are the door lock systems.

For the engine shutoff read about the injection pump.
Job 07.1-150

Check the brake system for vacuum also. Area 43 learn about the vacuum pump and its input to the brake booster

The EGR system uses some vacuum. Area 14.

And last the climate control system uses vacuum for some elements. Area 83. I'm not sure which AC ssytem your car has. this manual is for the automatic system. YOu either have just 1 element for fresh air. Or you might have 2 elements, fresh air and floor vents. What the manual can do is help you isolate the AC system so you can fix everything on the vacuum system.

1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
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