1984 300cd overdrive trans change up? - PeachParts Mercedes-Benz Forum

kosracing · #1 06-05-2008, 02:24 PM

HI there I am looking at purchasing a 2 door coupe 300cd was wondering if anyone has managed to replace the 3spd trans with something more recent like maybe a 700r4 or 4l60e? Or is there a standard trans conversion for this car? also does anyone have mpg numbers on these cars
thanks gary

#2 06-05-2008, 03:45 PM

The stock transmission in that car is a 4 speed auto. I do not know of anyone using a later auto transmission. This car was never offered in the U.S. configuration (turbo engine) with a manual. However some folks have replaced the auto with a 4 speed manual from similar parts cars (an advanced DIY project). More people have changed the differential to a higher ratio to reduce engine rpm (increase fuel mileage slightly).

In practice most folks get in the mid-20 mpg range. With lots of effort, some folks have squeaked out 30 mpg.

winmutt · #3 06-05-2008, 03:55 PM

The only standard conversion is to manual

As stated its a 4 speed if your not going through all 4 you have things to attend to!

#4 06-05-2008, 10:48 PM

There are no 5-speed automatics that will fit the engine, there is only the rare 5-speed manual.

kosracing · #5 06-06-2008, 10:30 AM

This car is a 1983 the owner tells me it has a 3spd auto, inregards to the transmission transplant I have been told that mercedes in that vintage dont shift the best (relying on a good vacuum signal for smooth shift). I plan on driving it on the hiway would like to drop the about 500rpm at cruize without effecting low speed torque thought the best solution would be adependable overdrive trans. I also own a cummins and a tdi both which start great in the winter, was wondering how is the mercedes for cold start and how is the heat output.

winmutt · #6 06-06-2008, 10:45 AM

Quote:

Originally Posted by kosracing

This car is a 1983 the owner tells me it has a 3spd auto, inregards to the transmission transplant I have been told that mercedes in that vintage dont shift the best (relying on a good vacuum signal for smooth shift). I plan on driving it on the hiway would like to drop the about 500rpm at cruize without effecting low speed torque thought the best solution would be adependable overdrive trans. I also own a cummins and a tdi both which start great in the winter, was wondering how is the mercedes for cold start and how is the heat output.

Its a 4 speed. Put a 2.88 geared rear diff in from an 85 300D/TD/CD. Can also be found on W126.

#7 06-06-2008, 10:48 AM

Quote:

Originally Posted by winmutt

Its a 4 speed. Put a 2.88 geared rear diff in from an 85 300D/TD/CD. Can also be found on W126.

That's about all you easily do, that will get you about 2-300 rpm drop at highway speed. I also run 205/70-14 tires, which will increase the gearing by a couple of percent.

rcounts · #8 06-06-2008, 02:11 PM

Quote:

Originally Posted by winmutt

Its a 4 speed. Put a 2.88 geared rear diff in from an 85 300D/TD/CD. Can also be found on W126.

Which years/models of W126?

mobetta · #9 06-06-2008, 11:10 AM

as stated- it is a FOUR speed auto. there are only 3 shifter positions, however- which must have the owner confused.

cold starts- that all depends on several factors-
compression
valve lash adjustment
battery(there's only 1)
gloplug circuit
oil(syn or dino)

my car w/ 290k started just fine down to about 10*f w/ rotella 15-40. I switched to semi-syn oil(rotella 5-40) and it will start down to -10ish is the coldest I have had to try w/ out a block heater.

a block heater will make it start in about any temps.

it is a 100% cast iron engine/ head, so it takes a while for it to warm up. of course, a block heater will help.

it will not get anywhere near the mileage of a TDI. but at least your friends won't see you in a VW

you can add OD units- gear vendor, etc- for $1k+

kosracing · #10 06-06-2008, 01:26 PM

hey thanks for the info. I am going to look at this car this weekend is there anything I should look for? My diesels all run esso (mobil) 0-40 syn. never plugged them in yet..

winmutt · #11 06-06-2008, 01:27 PM

Quote:

Originally Posted by kosracing

hey thanks for the info. I am going to look at this car this weekend is there anything I should look for? My diesels all run esso (mobil) 0-40 syn. never plugged them in yet..

egh. 0-40 is a nono. You want the 5w40. There are a number of posts in the TDI forums about bad oil tests with 0w40.

#12 06-06-2008, 01:31 PM

Yes, 0w oil is too thin.

kosracing · #13 06-06-2008, 01:41 PM

what were the finding in the oil samples? I was recently on a oil course with the maufactuer of the oil I run and they were saying no problems they still run high numbers of zinc were as a lot have reduced due to cat. failures

winmutt · #14 06-06-2008, 01:51 PM

Quote:

Originally Posted by kosracing

what were the finding in the oil samples? I was recently on a oil course with the maufactuer of the oil I run and they were saying no problems they still run high numbers of zinc were as a lot have reduced due to cat. failures

I couldnt quote it but everyone I know moved to 5w40.

winmutt · #15 06-06-2008, 02:15 PM

Dunno a variety of the first gen. You will need to swap the diff cover as well.