ideal highway cruising rpms for a 300d? - Page 4 - PeachParts Mercedes-Benz Forum

DeliveryValve · #46 01-05-2010, 02:23 AM

Quote:

Originally Posted by Hit Man X

Yes, SDL all came with the 2.88:1

Unless it is a 350SDL, then it came with a 2.82.

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Hit Man X · #47 01-05-2010, 03:04 AM

Quote:

Originally Posted by DeliveryValve

Unless it is a 350SDL, then it came with a 2.82.

.

Okay... where is this info from?

DANSMB · #48 01-05-2010, 03:51 AM

I have to chime in here as we have a 81 240D 4 speed with a NA 300 engine. After doing the conversion it was obvious the 240 gears had to go asap so after reading all this I put in some 3.07s. We live in Seattle where there are big hills on all of our freeways and I am sorry I didn't put in 2.88s as the 3.07s are still spinning the engine faster than it needs to turn, we have more than enough power to accelerate up the hills. Starting from a stop is no problem even on hills. If you are a flatlander I would even go with 2.47s.

Dan

MS Fowler · #49 01-05-2010, 06:52 AM

All this discussion has started me thinking( we know how dangerous that can be.)

Is there a place where all the available ratios and their vehicles are listed? If I decide to make a change, I need a shopping list for the junkyard.
Are all the diffs interchangeable?

I have an '82 300SD, that maybe could use some taller gearing.(lower numerical)

pawoSD · #50 01-05-2010, 07:01 AM

Quote:

Originally Posted by MS Fowler

All this discussion has started me thinking( we know how dangerous that can be.)

Is there a place where all the available ratios and their vehicles are listed? If I decide to make a change, I need a shopping list for the junkyard.
Are all the diffs interchangeable?

I have an '82 300SD, that maybe could use some taller gearing.(lower numerical)

We installed a 2.47 from a euro 500SEL into my dad's '83 300SD last May.....It is still decently quick, and feels totally different while driving. (very quiet and refined) Though the diff is quite loud.....as it had fairly high miles. Looked perfect inside though. A lot better than the 3.07 it replaced! It had metal shavings coming out with the gear oil and the gears were physically worn/damaged + it had a lot of play in it.

daw_two · #51 01-05-2010, 08:04 AM

Quote:

Originally Posted by MS Fowler

All this discussion has started me thinking( we know how dangerous that can be.)

Is there a place where all the available ratios and their vehicles are listed? If I decide to make a change, I need a shopping list for the junkyard.
Are all the diffs interchangeable?

I have an '82 300SD, that maybe could use some taller gearing.(lower numerical)

There was a recent thread (past 5 months???) that had some of that information in it.

I should chime in here that I have TWO early w126 gassers --- the rearends are still intact. One is spoken for.....the other is avaiable. If you do a search on "2 gassers" in the Parts Forum, you will find the thread.

daw_two · #52 01-05-2010, 08:05 AM

Quote:

Originally Posted by Craig

Do you know what gears you have, 2.88?

I would suspect (and hope) so. I've never looked .... nor changed it.

Brian Carlton · #53 01-05-2010, 08:20 AM

Quote:

Originally Posted by MS Fowler

All this discussion has started me thinking( we know how dangerous that can be.)

Is there a place where all the available ratios and their vehicles are listed? If I decide to make a change, I need a shopping list for the junkyard.
Are all the diffs interchangeable?

I have an '82 300SD, that maybe could use some taller gearing.(lower numerical)

You have two options:

A 2.88 from a 1985 300D or 1985 300SD.

A 2.47 from any of the V8 gassers from 1981-1985.

lutzTD · #54 01-05-2010, 09:14 AM

Quote:

Originally Posted by Brian Carlton

If it were me, I'd put the 2.47 in it. You'd cruise at 80 mph at 2800 rpm.

When you need to take a hill, you slow to 70 mph, use third gear, and climb it effortlessly at 3750 rpm.

I'm presuming that you do very little driving around town with this vehicle...........

I drove to Ohio from Fla in my coupe a while back, I have a 4spd with 2.47 and did not have any trouble climbing through Cumberland gap in 4th. I drove 75-80 the whole way, which is less than or around 3000 RPM. There is some sacrifice to city but it is only on initial takeoff, once the turbo spools up 1st becomes 2nd on a 5 speed. so it really only effects you if you come to a complete stop, otherwise it is like driving a 5 speed from 2nd to 5th. I like it so much I will most likely sell the 5 speed I have since it really is quite expensive to keep for no good reason.

DeliveryValve · #55 01-05-2010, 10:51 AM

Quote:

Originally Posted by Hit Man X

Okay... where is this info from?

Nowhere in particular. Just researched multiple sources and looking under cars for 1st gen and 2nd gen w126 ratios. Do a search and you'll find the 2.88 was last used with the 1987 SDL. In 1990, MB installed a 2.82 in the 350.
Here is the list. Feel free to correct if needed.

1st Generation
Years, Model, Engine, Differential Ratio, Differential Case Size
1981-1984, 300 SD, OM617.951 3.0L I5, 3.07, 1.1 Liter
1985, 300 SD, OM617.951 3.0L I5, 2.88, 1.1 Liter
1984-1985, 380 SE, M116.963 3.8L V8, 2.47, 1.3 Liter
1981-1983, 380 SEL, M116.963 3.8L V8, 2.47, 1.3 Liter
1982-1983, 380 SEC, M116.963 3.8L V8, 2.47, 1.3 Liter
1984-1985, 500 SE, M117.963 5.0L V8, 2.47, 1.3 Liter
1984-1985, 500 SEL, M117.963 5.0L V8, 2.47, 1.3 Liter
1984-1985, 500 SEC, M117.963 5.0L V8, 2.24 LSD/2.47, 1.3 Liter

2nd Generation
Years, Model, Engine, Differential Ratio, Differential Case Size
1989-1991, 300 SE, M103.981 3.0L I6, 3.46 1 Liter
1988-1991, 300 SEL, M103.981 3.0L I6, 3.46, 1 Liter
1986-1987, 300 SDL, OM603.961 3.0L I6, 2.88, 1.1 Liter
1991, 350 SD, OM603.97 3.5L I6, 2.82, 1.3 Liter
1990-1991, 350 SDL, OM603.97 3.5L I6, 2.82, 1.3 Liter
1986-1991, 420 SEL, M116.965 4.2L V8, 2.47, 1.3 Liter
1986-1991, 560 SEL, M117.968 5.6L V8, 2.47 ASR/2.47, 1.3 Liter
1986-1991, 560 SEC, M117.968 5.6L V8, 2.47 ASR/2.47 LSD/2.47, 1.3 Liter

1st and 2nd Gen Diff case comparison.

Photos courtesy of JohnHef.

EDIT: Added More Pics
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bgk202 · #56 01-05-2010, 09:01 PM

here's a link to an old thread with w123 240d diff and transmission gearing:

4 speed tranny gearing questions

sd300td · #57 01-05-2010, 09:18 PM

Quote:

Originally Posted by Craig

No one is saying it's going to fail tomorrow, it probably a matter of whether you will be replacing the engine at 350k or 400k miles. BTW, 21mpg is pretty low, mid-20s is probably more reasonable for your driving style.

Yep, I understand. I do a good mix of city/hwy. I've gotten 25 mpg on roadtrips before, but not typical for me as those trips usually require a full load of people and gear, and A/C in the summer...so its still 21-22 mpg.

I'm OK with that, the car runs strong and smooth and easily runs with socal hwy traffic.

bgk202 · #58 01-05-2010, 09:18 PM

Quote:

Originally Posted by DANSMB

I have to chime in here as we have a 81 240D 4 speed with a NA 300 engine. After doing the conversion it was obvious the 240 gears had to go asap so after reading all this I put in some 3.07s. We live in Seattle where there are big hills on all of our freeways and I am sorry I didn't put in 2.88s as the 3.07s are still spinning the engine faster than it needs to turn.

Dan

Did you loose any 1st gear acceleration when you went with the 3.07? Or was the diff just so over-geared that acceleration from a stop is the same (or better)? I have a 3.46 mated with a 300d na engine and a m/t out of a 240d. 1st gear feels odd (seems way overgeared) I want to shift out of it as soon as I get into it - I just acquired a 3.07 diff to put in - but am wondering how much (if at all) low speed acceleration will be affected.