1972 mb280 - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 03-23-2007, 06:45 PM Thread Starter
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Date registered: Oct 2006
Vehicle: 1973 MB 280
Location: Oakville, Canada
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1972 mb280

This is my 72-280. I bought it about 6 months ago and have been driving it since then without much trouble. I am planning to touch up some spots on it and buff/polish the paint this summer. In terms of automobile knowledge I am illitrate so please help me with these;
A friend of mine while riding with me in this car said that in his opinion it was reving too fast. I have noticed the engine rev high when I start it and when it is cold (specially in canadian cold winter) until the temprature reaches about 100 or so, but after that it somewhat settles down. What is the normal rpm for this model? After the engine has warmed up when I shift into drive the revs will drop a bit and if I shift back to N or P it revs Up slightly. is that Ok?
Also the oil presure shows 40 while on cruising speeds (70mph). But if the engine is warm and the vehicle is stationary (in drive "D") then the oil pressure drops to about 30. What does that depict?
All the lights except the dash board work. I checked the fuse box inside the engine compartment & found #6 fuse blown. But even after replacing that fuse the dash lights didn't come on. The low fuel indicator/hand break indicator lights do work though and so does the Hazard light & the one inside the shift box. Where should I look into to fix this problem?
Any help would be greatly appriciated and sorry for a lengthy post.
Kardar S
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post #2 of 3 (permalink) Old 03-24-2007, 05:19 AM
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Date registered: Dec 2006
Vehicle: 30+ mercedes
Location: Long Island, NY
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- Your car should have dual zenith carbs. They are setup with electric chokes (which means they work w/o your having to do anything). At initial startup, they choke the air supply a little and that causes the car to idle a bit faster. If you were to remove the air cleaner when the engine is stone cold, you should see a pair of metal flaps, one per carb that are laying down a bit. Once you turn on the ignition, current flows through fuse 4 and the chokes start to warm up and those flaps will move up. They don't move at the same rate, but they will both become vertical relatively quickly. The design assumes that you didn't just turn the key to watch the flaps move, but instead are actually running the engine at this time. In short, the behavior you describe seems to be normal.

- Separate from the chokes are two mechaisms bolted to the side of the carbs that push the throttle a little bit. They react to the A/C being on and the automatic transmission being in gear. Their design goal is to keep these two things from stalling your engine at a start or a stop. So once again, you are describing seems to be normal.

- The oil pressure guage is reading live pressure; it's not an electric gauge (remember that if when you go to remove the gauge cluster). At anything other than idle, the gauge should be pegged. While idling, the gauge probably reads up to the 1st white tick on the face. Touch the gas a bit and it will peg the gauge rather quickly. I believe you and I just said the same thing.

- Dash light brightness is controlled by the small knob to the left of the odometer (the control is rightly called a reostat). It's black; you might have missed it. There is an identical knob on the right. That one resets the trip odometer. Turn on the lights with the big switch and then turn the brightness control back and forth a few times. These old switches get corrosion from sitting in one position too long. If a dozen back&forths don't get you some evidence of lights, then the next step is to remove the gauge cluser and use a multimeter on the reostat.

Removing the gauge isn't complicated, as you need only give it a gentil tug to pull it out. Most of the things that hold it down can be unplugged or unscrewed. The exception is the temp guage pipe. That's a thin, flexible metal line. Don't kink it or break it. But it's long enough to put the gauge on your lap if you're careful.

Now, your next assignment is to check the historical posts here and at the other benz self-help sites to see if somebody has described how to fix that reostat.

If you intend to get your hands dirty and want the service manual, just call 1-800-for-merc and ask for it. It's about 30$US.

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post #3 of 3 (permalink) Old 03-25-2007, 04:22 PM
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Date registered: Jan 2007
Vehicle: 1973 280C
Location: Ontario, Canada
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nice to see another from Ontario on here! I am in kingston, with a '73 280C
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