240D Final drive ratios.

[dieselrattle]

Hi all.
I just bought an '83 240D, and am generally very happy with it (once I replaced the front brake rotors, which was supprisingly easy). The one thing that irks me is that it seems to have an inconveniently low gearing:
I shift out of 1st with the car barely rolling
I can easily start in 2nd, especially compared to my torque-free Civic.
I tend to shift into 4th by about 40 or so.
Above about 60mph it seems to really be past it's optimum.

Is it simply that I like the sound of a slow-turning enginer too much (I do know about the shift-point dots), or is this something that I should think about having fixed.
I work with a bunch of off-road warriors who swap out differential ratios like a DJ swaps records. Would the same operation be possible on my new baby? Has anyone else tried it? What is the stock ratio?

Thanks for your ideas....

[fredjj]

It may take a while to get used to but your 240D is doing what it was designed to do. My commute is 100 miles r/t and 80 of that on highways doing 75-80 mph. I've heard about swapping 300D (N/A) differentials into a 240D. I wouldn't do it because acceleration would be even slower and I'm not sure if the 240D has the tourque or power to pull that gear up to highway speeds. Additionally if you live in a hilly area it may be dangerous. The one modification I did was replace my radiator with one from a 300D. Now my coolant temp. only approaches 200F on very hard runs instead of going up to 210-215 just cruising at highway speeds. Others will add in their experience as well but in general the car is doing what it was designed for. Letting it rev keeps it clean and long lived.

[R Leo]

These engines are made to spin...soon enough, you'll be used to the bellicose yeowl of an OM616 at speed.

[fredjj]

for sure 'tis a beautiful sound to the well trained ear.

Get used to it, or find a Euro 5 speed. They are designed to run high RPM on the highway. My 5 speed is absolutely lugging under 60 mph.

[fredjj]

Diesel Power, does the 5 speed allow a higher top speed or just fewer rpm's at speed versus an Auto. or manual 4 speed?

[Wasuchi]

All these MB Diesels are meant to rev high... almost like a gasser. My 300D will rev to 4500+ before shifts if I really stand on (like if I pull out into a busy road from a dead stop). They are happy to run at 3-4k rpm all day long.

Originally posted by fredjj
Diesel Power, does the 5 speed allow a higher top speed or just fewer rpm's at speed versus an Auto. or manual 4 speed?

My assumption is for higher top speeds since this is car was originally sold and used in Germany. I haven't yet taken the time to find a long open stretch of highway with a borrowed radar detector to open it up till it won't go any more.

I have a short laundry list for the car after I complete the house remodeling, so I'm not driving it much right now.

[fredjj]

Gotta' have priorities A five speed would be nice for those long flat empty stretches of interstate. We drove to South Dakota last fall and had the 240D nearly flat out ~82 mph all the way across Iowa and SD until we hit the Black Hills. We were still getting passed like we weren't moving.

[dieselrattle]

So the consensus is that I should just push down with my right foot. I certainly didn't think that Mercedes would build a car that couldn't cruise at at least 70mph, even for Americans.
Very well then, I'll just have to get a louder sterio.

Thanks

[psfred]

Wind it on out -- rev limit is around 5000 rpm, and that will give you about 85 mph -- the last mark on the speedo will be about there. May be 90.

My 220D tops out at 84, the 75 300D my brother has tops at 95, my 87 300D goes way to fast (no mark, but the book says 129 mph max speed).

Just get used to the sound, this isn't a sissy Jappo with a very tall rear end. You will find you have excellet throttle response all the way up, too!

Peter

[300SDog]

If you are going into 4th at 40mph, then you cant be following the speedo shift points..... probably bottoming out all your gears because you are not used to narrow band, high torque diesel characteristics with lotsa special effects that make you think the engine works harder than it should.

I like 3rd at 45-50mph and wont touch 4th below 55, unless am coasting or just gliding along on flat stretches of road.

However I'm driving '79 240D with just 118k miles.... so its possible that higher mileage machines favor lower rpm ranges, especially if they've been lugged at low rpm's by previous owners. My feeling is diesels break-in as either high rpm or low rpm engines within their power band.

At any rate, try peddling through the gears at *** 25-35mph (2nd/3rd) and 50-60mph (3rd/4th)*** Try shifting gears often at these recommended ranges and see how the car performs.....

Instead of just thinking on shift points as red lines... think on them as minimums for the next highest gear. IOW, shift mark III can indicate low rpm range at 4th gear or high rpm range for 3rd.

Most endearing quality of the 240 diesel is it matches engine speed with typical around-town driving habbits. I will argue all day long that 4-spd 240D is superior to automatic 5cylinder at achieving attunement between driver and normal driving conditions..... literally making the 240D owner the best driver on the road.

LOL, get away from the Honda Civic with broad power band slushiness and basic isolation of driver from engine..... the little gasoline car can teach you nothing about appreciating your new 240Diesel. Basically, gasoline engine driving habbits create bad diesel engine driving habbits.

[psfred]

Those marks on the speedo are redline (maximum engine speed), not suggested shift points. Under light throttle, 4th at 30 is fine, but performance will be, well, leisurely.

Shift whenever you want -- for best performance, upshift about 5 mph less than the max speed from 2nd to 3rd and 3rd to 4th. The torque falls off pretty badly at the very top of the rpm range.

Peter

[Ron in SC]

dieselrattle,

You might as well get used to the car the way it is. I had an 83 240D with a manual 4sp. I too looked into putting in a different rear end but found it was not financial feasible.

When I sold my car about 5 years ago it had 276K miles on it. I never had a valve job or anything at all done to the engine. It reved high on the interstate at 80mph, in fact it sounded like it was going to come apart. Of course it didn't. Frankly it was probably one of the best cars I ever had from the perspective of being bullitproof, and very easy to work on.

[300SDog]

>>>Those marks on the speedo are redline (maximum engine speed)....

I'd like to hear someone with tachometer tell me exact engine speed at each speedo mark, hard to believe each is at 5,000 rpms..... but i could be wrong.

>>>Under light throttle, 4th at 30 is fine.....

Has anybody who drives their 4-spd. 240diesel everyday tried this?? Its impossible!! - also a very good way to overstress and damage the engine over long periods of time.

>>>..... for best performance, upshift about 5 mph less than the max speed from 2nd to 3rd and 3rd to 4th.

Once again, there goes the idea of using 4th below 50mph down the toilet...... unless you decide to skip 3rd and go straight from 2nd into 4th at 32mph shift point.

DieselRattler - stick within recommended ranges for each gear as indicated by shift points.... its an acquired taste, bombing along in 3rd gear for extended periords between 40 and 50mph... but it should be the best range for engine performance, comparable to 75-80mph in 4th gear where the motor can wail all day long.

Lugging these engines and bottoming the gears is easy to do.... but once you get used to narrow power band diesel, gasoline engines just wont be fun anymore.

As I've said, endearing qualities of the 240D include forcing the driver the optimize engine performance to the max with lotsa special effects and engine racket.