As you all know I have two Benzes a 1979 300SD.....and a 1983 300D.

I have almost a 1,000 RPM difference between the two cars on the road at 70 mph.

Both are the 4-speed automatics....both have differentials stamped with 3.07. Both run tires nearly the same diameter.......This baffles me. The 300SD cranks way more rpms on the road and it IS shifting through all 4 gears. with minimal slippage (as all automatics have some).

You can audibly hear the differences, its very noticible...so its not a tach inaccuracy thing.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Maybe the ratios comming out of the trans are different? Its a bigger heavier car with a towing capacity, that would be my GUESS.
Wodnek

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes

No, high gear should have a 1:1 ratio, aka "direct drive" on both trany's well, as direct as you're gonna get with an auto-trans

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-Randy Wakefield

1969 220D 4 speed (parts car)
1976 280C
1976 280S
1981 240D 4 speed (parts car)
1982 300D
1983 300TD (Ivory)
1983 300TD (gold)
1985 300TD (gray)
1987 190D 2.5
1970 280SEL (sold)
1977 240D 4 speed (sold)
1974 280 (rusted to death)
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1927 Chevy 4 door sedan
1938 Chevy 2 door sedan
1950 Willys Jeepster
1955 Studebaker President 4 door
1977 Ford F250
1979 Glastron 17'
1948 John Deere A
1960 John Deere 2010
1979 Satoh S650G
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2000 Bichon (Doby)

Well as far as speedo accuracy.....morning traffic averages about the same...70 mph is normal in light traffic areas.....plus I have driven by stationary radar at limit and thats what others were doing...( and we are talking 30% difference here) ....and since these things are nighmares to rebuild I am assuming they have the original gearsets in the housings.

No I havent jacked the car up to turn the driveshaft and count the turns on both....which is hard since the availible space in my driveway is not flat and car would roll on the jack.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Bonehead, Cannot really see wrong rear end gears but anything is posssible. Suspect one transmission by malfunction in passing gear mode perhaps rather than final drive. Do not know much about automatics unfortunatley. Just trying to generate ideals. Could be something as simple as a linkage problem or kickdown switch if lucky. At least I am relatively certain it's not your glow plugs. just re read your description. Possibly torque converter is slipping far more than normal? They can go bad of course. Have a look at that transmission fluid as well. Hope someone with more torque converter experience chimes in.

I think Barry has a good idea there, the trans on the SD might not be going into high gear. What RPM's do you see in each at 70? 3000 and 4000? Also, it's possible the torque converter on the SD is on the way out. Hope not.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

That is very odd indeed. My only guess would be the speedo is off, but by that much though???? I'd like to see what other people have to say about it.

__________________
-Randy Wakefield

1969 220D 4 speed (parts car)
1976 280C
1976 280S
1981 240D 4 speed (parts car)
1982 300D
1983 300TD (Ivory)
1983 300TD (gold)
1985 300TD (gray)
1987 190D 2.5
1970 280SEL (sold)
1977 240D 4 speed (sold)
1974 280 (rusted to death)
---
1927 Chevy 4 door sedan
1938 Chevy 2 door sedan
1950 Willys Jeepster
1955 Studebaker President 4 door
1977 Ford F250
1979 Glastron 17'
1948 John Deere A
1960 John Deere 2010
1979 Satoh S650G
--
2000 Bichon (Doby)