You might want to do some research on that. On the 1982 300SD and 1983 300D we have here in the driveway the transmissions and differentials are different and are not interchangable. If you find some documentation to support your claim please let me know as I would be VERY interested to know!

In regards to the wheelbase options the earlier cars were all short wheelbase cars but later models were available as an SDL on the 126 chassis. I was referring to the 126 chassis. SD would be the S class Diesel and SDL would be S class Diesel Lange (long wheelbase).

In regards to the speed differences my brother and I don't drag race our diesels so a 0-60 test is something we dont have. Between the two cars the SD just goes faster probably because of some different gearing or tuning. Both cars are maintained to similar standards are only a year off of one another age wise and have "similar" mileage.

W126's were made in both long and short wheel base, for the entire production run.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

that may be true but the early ones are very very rare in diesel long wheel base i think. i dont think i have ever seen one. now the later 126s the short wheel base is very rare. i dont think i have ever seen a short wheelbase in the later years.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I've never seen a long wheelbase in the years '81-'85.

I though the '81-'85 W126 long wheelbase was only available as an SEL (gasser), not as an SDL?

Yes, I think you are right. I should have stated that I have not seen a diesel long wheelbase in the years '81-'85.

I've heard of gassers with the long wheelbase in those years, but, I don't think I've seen one yet.

Correct I am talking about world wide W126 production. The diesel W126's are strictly a North American thing.

For example from 1980-85 you could get a 500SEL or a 500SE. A 280SE or a 280SEL. (came with a manual trans), plus many more.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

im looking at U.S. only and 300D turbos from 83-85
and 300SD from 80-85. (turbos as well)

now we can nail it down.

the sd is 130 lb heavier according to the website "mercedes us models". the engines trannys and rear end ratios are virtually identical. the s class is longer but more aerodynamic. the front track is pushed out a bit to provide more room under the hood for v8s, the rear track stays the same as the 123. there appears to be a bit more width in the front seat area but it probably is only slight. the rear seat has a bit more legroom than the 123. the s class trunk is a bit taller i think and a bit longer. in performance, the 123 feels a bit more nimble around town but the s class feels better on the highway. the s class ride is a bit better imho. there is not much difference in fuel economy. i think perhaps the 123 might do a bit better around town and the s class a bit better on the highway. the s class prob has a bit less wind noise at highway speeds. the s class has a few more gizmos to maintain when it gets old like power seats. the ac system is pretty much the same in function and reliability. the s classes have mostly leather interiors and the 123s mostly are mbtex. the leather is a little more friendly to the skin imho and the mbtex is a little more durable, though if leather is religeously treated it may not be just as durable.

oh and the 126 will need front end work sooner than the 123. except for the tie rod ends which go bad on them both about the same. in my expereince you start having bush issues in the 126 around 100k, and in the 123 it may not be til 200k.

so not a lot to turn a decision, but i think it is generally agreed that the 1213 body is simpler and cheaper to maintain, but the difference isnt great. they both are very well built cars with few significant weaknesses.

find the cleanest car you can and check it out really well and enjoy. they both are good, safe and enjoyable to drive and work on.

and as a side bar reference to another thread, my mercedes buyers guide says the the cd was turbocharged starting in 81. it could be wrong, i have caught it before.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I'm certain that your 300D and brother's 300SD should have the same differentials. From 1978 to 1984, the 300SD had a 3:07 rear differential. For 1985, it had the 2:88. From 1982 to 1984, the 300D used the same 3:07 differential and in 1985, got the 2:88 as well. It may be that someone swapped the differential out in one of your cars for the 2:88, it's a kind of popular mod on MB diesels now.

W126 Differentials
http://www.adsitco.com/category.asp?CID=418

W123 Differentials
http://www.adsitco.com/category.asp?CID=416

W123 info sheet (1981-1984)
http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/Chassis/00-040.pdf

And as far as the transmissions being interchangeable, you still can interchange them, though you'll have to swap out the tailhousings to make them work, since the 300D uses a speedometer cable, and the 300SD uses electronics.

__________________
'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

They did start turbocharging the CDs in 1981, but they were being made as 1982 year models. Only 777 turbocharged CDs were made in 1981. Maybe the guide meant TD instead of CD, since the 300TD was turbocharged for the 1981 model year, but they started making those in 1979, there were only 2 made in 79 though.

__________________
'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

that is close enough for me. i dont know how many us cds were built in 81 but i wouldnt be surprised if that is all of them. the're kindof scarce.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Don't confuse the the gear ratio with the outside housing, and mount points.


For example the SEC's use a different diff mounting system then the SEL's.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

yeah, good point. i was thinking of ratios and engine performance. the housings may be different. i dont know.

i didnt know about the sec mounting being different. the rear large a arms are forged or cast aluminum on the sec too, and i think the suspension may sit lower. the wheels sit further out too i think. same as an sl, not a sedan. the handling of an sec is very sporty.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

All 300CDs were for North America. Counting the 777 turbocharged 1982 year model 300CDs they made in 1981, and the 335 non turbo 1981 year models they made then, we have a grand total of drumroll please... :-D

1,112. Pretty rare for a diesel MB ain't it?

__________________
'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.