If you install a 300 turbo with a 300 auto transmission, in a 240... then you will get a 300. 240 and 300 are the same car, except
for different engine and transmission.

cp

OK, the auto's may be a different matter. I'm interested in the whole
auto-tranny interchangeability thing myself, since my reverse on my 300
turbo is very weak, and I have a tranny from a non-turbo 300. I suspect
that the 240 auto transmission was originally engineered for the 240 and
that the 300 auto had some upgraded parts - and the turbo auto tranny may
be the same deal. On the flip side, at least on 300s, if the transmissions
ARE different between the turbo and non-turbo, then why do the turbos
have a higher rear-end ratio - if they were re-engineering the trannies
for turbo use anyway, why not change the gear ratios in the transmission
and use the same rear-end?

As far as the manual transmissions go, I suspect that as overbuilt
as the Germans tend to make things that the manual transmissions
are more likely to be interchangeable than the autos - but I do not know
this for a fact.  My best guess since the bodies have the same mount
points that the only difference would might be the overall transmission
length - which, if different, would necessitate swapping driveshafts
also. Got a tape measure and access to both vehicles? If the drive-shafts
are the same length (and I mean exactly the same - to the millimeter)
then I would think it would be doable without swapping driveshafts. I'd
be a lot less nervous about putting a 240 manual on a 300 turbo than I am
about swapping auto trannies - the most likely area of concern I see would
be in the clutch bits - it's possible that the correct 300 turbo clutch
parts are stronger than 240 clutch parts.

This is all pure conjecture. Anyone got one of those nifty W123 diesel
parts books with all the part numbers?

In the U.S.? Was overdrive available elswhere? Either way, the diesels
have such a flat power curve that I'm not sure overdrive would gain
you much. Besides, I bet if you look at the tranmission ratios that
the high gear is a little taller than you'd expect - kind of overdrive.

Conrad

I did the exact conversion that you are talking about.  I drive a 1979
240D. About four years ago the oil pump quit and took the engine with
it.  I had the option of rebuilding my 240 engine, selling the car to
someone with a good engine and a wrecked body, or doing an engine swap.
   It just so happens that I was talking to the guy who does body and
paint for me, and he had a 300SD which had been totalled in a rear end
crash.

I had the engine installed and kept my original 4 speed tranny.  The
tranny that came with the engine was an automatic, and the surgery to
install that in my car was a problem I didn't want to deal with.  I did
have the transmission fully overhauled at that time.  I did not change
out any gears or anything funky.

I've been driving it since around 2001, have had zero problems with it.
I get about 22-25 US mpg. (26-28 if I can find biodiesel).  This is the
same mileage as I got with the 240. The major difference is POWER!  The
240 is rated at around 67 hp, and the 300 turbo at ~120 or so.  Can't
remember the exact numbers.  I live in a mountain state, and the
difference climbing hills, or even doing freeway onramps is amazing.

In the 240, I was climbing hills in 2nd, maybe 3rd, doing about 30-35mph
and staring at the semi about to use me as a hood ornament.  Now I can
actually have a fully loaded car, 4people & luggage, and climb the same
hill at 55-65.  <G>  Much better!

The 240 may be a fine engine for city driving, and highway on the flat,
but it just isn't enough for mountains.

Rochelle