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When should my transmission shift?

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monarchd's picture
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I just bought an 83 300D Turbo. It came with a rebuilt transmission among other repairs. I've only been driving it for about three days.

Here's when it shifts. It goes into 2nd around 15mph, 3rd around the low 20's and then 4th as soon as the late 20's then does not shift again no matter how fast I go. It runs strong. The engine has 180k on it. This is normal driving, not punching it. This also happens in about 5-6 seconds. Seems very quick. Is 4th gear made to run from 30mph all the way up to 90mph?

My question is if those are the correct intervals. It seems to be revving pretty high when I get over 50 mph but I'm starting to think that might be normal for these cars. I've ran it at 80 and 90mph and it seems to be fine. I've found some posts that touch on the subject but in reference to other issues. I migh be fine but I don't have any experience to know.

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pch2021's picture
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youre doing fine on the shifting, just make sure the red collared passing gear cbale is connected
also, dont run so fast. 70 is a good speed in these cars.

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Pierre Hedary
...happily servicing vintage Mercedes-Benz in sunny Florida...
1972 280SE 4.5 252K
1970 280se 3.5 coupe 108K
1971 300sel 4.5 121K
1991 420SEL TMU, but looks brand new!
Mercedes technical advice: 407 765 2867

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I usually do keep it down. I just wanted to see what it would do. Thanks for the help.

Also, where can I get "Purge" and the water removal addative. I looked at PepBoys and couldn't find it.

Thanks agian for the help.

Mark

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pch2021's picture
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diesle purge? well, i can sually find it at carquest or bumper to bumper.

Also, to relalyt get water out, flush your tank.But water in diesel is usually not as common an occurence as people think.

your car shold be turning 2250 rpm at 50 mph, 2550 at 60, 3000 at 70.

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Pierre Hedary
...happily servicing vintage Mercedes-Benz in sunny Florida...
1972 280SE 4.5 252K
1970 280se 3.5 coupe 108K
1971 300sel 4.5 121K
1991 420SEL TMU, but looks brand new!
Mercedes technical advice: 407 765 2867

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1987 300TDT

Gentlemen,

I've got to correct a discrepancy regarding over-reving the motor. 123 300D has an OM617.952 engine. Mechanical fuel injection pump, which has a governor that will limit maximum RPM to 5200 with no load. In the maintenance manual there is a procedure to test the fuel injection pump by holding the accelerator down to see if the engine can reach max. rpm. MB would not put this procedure in the maintenance manual if it were not safe to do.

If you leave the gear shift in L or S, and floor it, RPM will probably get to 5000 and maybe a little more, but the engine will not blow up as long as the timing chain is within spec and it has good clean engine oil and proper fuel. I wouldn't abuse the engine by holding that speed for long, but one should not fear reaching such a high RPM. Notice that there is NO RED LINE on the tachometer!!!

Now, it is possible to over-rev the engine by manually down shifting at high speed, and forcing it to over-rev by using the car's momentum. However, if all systems are working as designed, you will never be able to damage the engine by pressing on the accelerator pedal. These engines have a reputation for being bullet proof; they did not earn that reputation by self-destructing like some gas burner!

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Max Dillon
Charleston SC
'87 300TD, 334k miles (head is off, getting ready to install a different used head...)
'95 E300 Diesel, 348k miles (daily driving duty)
'73 Balboa 20

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Maxbumpo's picture
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1987 300TDT

Your first anecdote is what I'm referring to - using the car's momentum to over-rev, in this case aided by a large hill.

Yes, I'm sure that an injection pump can break in such a way that it will allow the motor to over-rev. We could play 'what-if' all day and think of terrible ways to destroy an MB. However, injection pump failures are very rare, I think.

The real nightmare is a run-away engine, :eek: wherein it begins to consume it's own motor oil as fuel, and cannot be stopped unless the air can be removed (by filling the intake with CO2 from an extinguisher, or putting a stout board over the intake manifold). This usually occurs when someone overfills the crankcase with oil by several quarts or more, or when the vacuum shut-off assembly is incorrectly installed so that it forces the fuel rack inside the injection pump past the governed limit, and when the engine is started it immediately climbs past 5200 RPM and self-destructs.

So, don't overfill your crankcase by 2 or more quarts of oil, and follow procedures exactly when replacing the vacuum shut-off assembly, and test it for correct operation before starting the car. :D

As to the parts car, they probably allowed it to run low on oil, used an improper fuel (ether anyone?), or allowed it to overheat.

Anyone ever notice that when an American made car breaks down, it is the car's fault, and when a German car breaks down, it's "Oh my, what did I do to my car!?"

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Max Dillon
Charleston SC
'87 300TD, 334k miles (head is off, getting ready to install a different used head...)
'95 E300 Diesel, 348k miles (daily driving duty)
'73 Balboa 20

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Robby Ackerman's picture
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Over revving is hard to do

I had this experience with a new Peugeot 604 SRD. It was built along side the W123s from mid-70's to mid-80's. The SRD is a 2.3 liter turbodiesel with a five speed manual, body by Pininfarina and actually has more space and noticeably more comfortable ride, particularly for the back seat passengers, gets better fuel mileage (30 in town 35 highway), brakes last longer (front pads 125k never replaced the rotors) than the 300D. My wife bought one new in 1983. Twenty years latter she gave it to the Kidney foundation. She'd still be using it but there has been no dealer in the USA since 1991. She did well to keep the car going for 12 years after Peugeot pulled out of the USA market.

So much for brevity. She was driving along at 70/75 in fifth gear climbing a 7,000' mountain on the freeway just north of LA. I suggested she shift down to fourth for the long climb. The car was new and she hadn't driven this car many miles yet. As she shifted down into fourth she actually pulled the shifter to far to the left and dropped it into 2nd at 70 mph. Second gear was good for about 40 mph. The rear wheels decelerated so quickly that she laid a patch on the asphalt with an ensuing cloud of smoke. End of story. She went on to drive that car for more than 600,000 miles. The transmission was never touched and the only work done to the engine was a timing chain & ring replacement at something around 350,000 - 400,000 miles.

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1960 190 SL
1983 300 D (WVO)
1984 190E 2.3-16 / Mosselman Turbo System & Dinan suspension
1984 190E 2.3-16 / Delsing Motorsport suspension
1992 500SL


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