Hello all,
I am curious to know what the stock differential ratio is in my 79 300D. It seems quite high (3.69?) considering the engine sounds like its running fast at 70 mph (no tach). Also, is there any way to swap in a diff with a lower ratio from a later 123 or 126?

Hello MB123Diesel - welcome to the forum

There are loads of threads / posts about this on this forum.

The ratio 3.69 is correct for your car (and mine too). However a lot of people change it for a 3.07 to get higher cruising speeds.

it is not 3.69....

its 3:46:1

where do you get your info from?

__________________
1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

You have a 3.46 as Oracle said.

240D's got the 3.69 rear diffs.

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

Yep sorry - I'm numerically challenged:-

http://www.peachparts.com/shopforum/showthread.php?t=263096

I recently swapped a 3.69 into my 617.912 300TD, 722.118 in order to get two features:

1)Crisp "around town" acceleration, which the 3.07 did NOT have in this
"non-turbo" car! I can now protect my lane on two lane, 35mph streets from
the midwestern scoundrels that are constantly hunting for a "lane grab".
It has great midrange acceleration for on-ramps, which it did NOT with the 3.07. it pushes third
gear up to around 38mph, rather than the "too late" 46mph that the 3.07 forced!
The 3.07 makes for a lousy "on ramp" blender, where you would like to be on
the torque curve between 35 and 55. At least in wisconsin, where traffic does
65 or so, and ramps are generous in length.

In california, where ambient can be 80, and ramps aren't long ...
think carefully about what feature set you consider important. Ditto, new england. I dunno from netherlands.

2) A W.F.O. "top speed" of 74 mph, which is plenty. And the car will comfortably
cruise ALL DAY at this speed when properly setup, as proven on my recent 2,500
mile trip from WI -> MA -> ME -> WI, all done with my foot "in it". It can climb
maximum pitch interstate hills and still have headroom to pass the "slow going" RV's,
trucks, etc -- which it did NOT with a 3.07.

its a diesel. when the upper limits of the pump are correctly set on a healthy engine,
its spins well, and quietly -- at top rpm speed, with 195/70-14 tires>. I, for one, think the "lower gear diff" swaps are
highly over-rated.

So, I would recommend having your pump setup with care BEFORE making the
decision to change for "better cruising characteristics". YMMV.

I only sacrificed 4-5mph at "top end" making this change. The 617.912 couldn't sustain
80mph even when it had a 3.07!

__________________
--frankb

1982 300TD 617.912 <NLA> . 1975 2002 E10-EFI . 1976 914c6 . 1983 MG LMIII <NLA>. 1988 Montero / 616<NLA> . 2001 TLS . 2005 Saab 9-5 Wagon

I gotta agree. n/a vehicles need to keep the stock 3.46 rear. if you are lucky enough to have a 5 speed manual like me, you can get the best of both. crisp accel, and decent cruise!

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

There is also a 3:58 Diff used on some of the Euro Grey Mkt cars I have seen at PNP.
I have seen 3 in the past year. usually they have a 150mph spedo.

There is a reason the engeniers place a certain gear ratio behind an engine.

I learned this first hand on my 82 datsun PU with the 4 cyl NA, 60hp Diesel engine. truck came with the 3:889 Diff. I decided to up grade to a 3:56. we went on a trip to ABQ, NM. and the fuel milage droped and the ability to keep up the speed droped also. the engine had to work harder.

Replaced it with a 3:07, and the same thing.
finally we are back to the 3:889 and she is happy with it.

As a rule of thumb, the lower the Hp, the lower geared the Differential will be.

Now that Iam the proud owner of a 240D with the 3:69 Diff, she seem to accelerate reasonabley into the freeway traffic flow. I can only imagine how slow a 3:46 would be .


Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works