gear ratio question
 

I have the oportunity to purchase a 2.24 ratio rear end for my 300d turbo. I have always wanted to go to a lower ratio for highway driving but do you guys think the 2.24 would be going too far. This diff would only cost me $75 and there are only 2 bolts left holding it in. That appeals both to my lazy and my cheap nature. It is currently hanging from a 500 SEL of unknown mileage.
P.S. I did search this forum and could not anyone that has used the 2.24 so you don't think I'm that lazy!

Rear differntial ratio will have an effect on your outcome.

Axle ratio (:1) 2.24 suited for a 400E, suggest big power output!

An axle ratio of (:1) 3.27 from a 260E would represent a lower power output.

Diesel plants in our 300 D and SDL, require 2.87, or 2.65 ratio, compaired to gassers higher ratio.

Does this give you any more perspective? :confused: I'm confused!

your mileage
 

should be fenominal (sp)? and your acceleration times from a stop. on the other hand once rolling it wont make much difference.
it might be a posi too. that would be a euro car, right?

tom w

What?????

i dont
 

think the 2:24 was offered in us spec cars. and if so it may be a posi. no kidding.

tom w

2.47
 

I have read so much about guys using the 2.47 ratio I wondered if anyone has used the 2.24. Every one that has tried the 2.47 loves it so I wondered if the 2.24 would be too high a gear ratio or just a little more of a good thing. According to (I think it was) brian carltons formula the 2.24 with 28" diameter tires would put my engine rpm at 2190 at 75 mph. I am impressed with the power of this car in all the conditions I have driven it at. My crazy wife has managed to get across the top of vail pass at 85 mph with 3 kids and all the crap that goes along with them so power does not seem to be a problem. And it gets 23 mpg city/ highway driving combo which seems pretty good considering the way she drives.

Everything I have read states that maximum fuel economy with a diesel occurs if the engine is operated at or just slightly below its torque peak when at cruising speed. I believe the 617 torque peak occurs at 2800-3000rpm. The factory 2.88 gears are almost perfect for 70-75mph cruising. This gearset with slightly taller tire to lower apparent gearing to @ 2:70 or so would probably be perfect. I think going to a 2:24 would lower the rpm so drastically that it would be hard for the engine to build enough rpm to start spooling the turbo up when you encounter a steep grade, like you do in CO. The 2:47 gears are probably a little too tall as well for mountain use but would likely work well in a places that are flat. Just my 2 cents. RT

Can always change it back if u didnt mind the work.
I heard an old guy didn't even let it on 4th in his F250 Diesel p/u. Reason not enuf RPM will hurt tranny.
Or you keep her in 3rd during city driving, and go on D when u hit the Autobahn.
The way MB designed to run all 4 gears before u hit 30MPH, in a way is a waste of time. Unlike most design to let 4th to kcik in until a much higher speed.
So beware if the tranny is lugging too much. And quite often the significant 1/2 doesn't follow instruction very well at all. Tend to leave her in 4th then u need a new tranny in the not too distant future.
If your area has a lot of hills, then maynot be a good thing.
Also remember back in the days of Iran/Iraq war circa 80s. GM some how was going to supply Iraq a whole bunch of Cheby Malibu. The deal got kyboshed. GM had to dump those in Canada. As those cars were all equipped with very tall rear diff. Low 2s. And running them in Canada is not too suitable.
I guess in Iraq was pretty flat, so u can have a 2.00 rear end and still run well.

Is there a ratio stamped on there? Posi-trac or limited slip could be a nightmare when driving on snow. As both wheels lock up when no gas is applied. make the fishtail happy. So we need to be careful what we prayed for!

although
 

i have never had a car with posi i have had several trucks including my present tow vehicle an 03 dodge cummins with sixer. when the snow flies i put seven seventy pound sand bags in back and it goes just fine in the snow. i have never noted any extra tendency toward fishtailing under decel. under accel it is not a prob either. the dodge has 500 torque and it comes on rather suddenly because of the turbo, yet it still is not a prob.

that said i cut my teeth driving in snow. and as a youngster drove a quarter midget some on muddy clay tracks. so driving sideways does not intimidate me. i just make sure the side windows are cleaned off.

tom w

Stock W123 tubo diesel 82-84 is a 3.07 (as stamped on case)

decision
 

I went out today and took another look and decided against it. I figured it might be past the point of diminishing returns. I did get a chance to look at a 560sel and it did have the "easter egg" 2.47 but the damn thing mounts differently. On a positive note I found a 83 300d turbo so I robbed a whole lotta interior parts for $60 so all was not lost. Now I can even change the front signal light my wife smashed off. I wonder how many cars she leaves burned and smashed in her wake?

Posi-traction and a lower diff ratio (for those better mileage numbers) would be feasable as an adjustment if you upped your engine HP.

I have a few rear ends out of some cars of old guys that bomb from LA to Vegas in their 560SEL's (etc).

I figure I'll look at doing the diff. after I damage it due to too much torque ;)

Differentials are pretty strong!
I know a guy near LA that has a 560SLC with a huge 375 HP Chevy V8 in it :cool:
He found that the weak link are the half axles, he bent up several sets before finding something that would hold up to all the torque that was being served to them :eek:

OMEGAMAN, I would go with the 2.88 from an '85 diesel and stay there. You'll be happy

[QUOTE=boneheaddoctor]Stock W123 tubo diesel 82-84 is a 3.07 (as stamped on case)[/Q I have a 80 300-D none turbo and changed from a 3:47 to a 3:07. I gained 8 mph at the same rpm. the car now runs fwy speeds and sounds like its not roaring down the road. my fuel milage is the same 28mpg but think the eng. will last longer. if you go to tall it will suffer on the low end pulling power.

when you say
 

your mileage is the same are you correcting for odo error or did you change the odo?

in my experience you should be getting better economy.

tom w