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  #16  
Old 10-27-2009, 11:59 PM
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Quote:
Originally Posted by t walgamuth View Post
Not likley in my experience. (sorry to disagree, Dan). In a diesel swapping in a taller diff has always worked well for me.

I am running a 307 diff in my 83 240 with euro 300d motor. With the four speed I got thirty highway regularly. I swapped in my five speed and now get 35 36 regularly running 70 to 75 mph.

I could pull a slightly taller gear...maybe a 288 but taking off is already a bit dicey with the 307 rear end.

(the 307 with the 18% od is about equal to the 247). You'll never get 37 running an automatic imho....unless you run about 50 mph).
ymmv.

Has a lot to do with the engine tuning. Cam chain enlongation on these old 617s have shifted the torque to an even higher rpm now. Perhaps if if seems like you could use another gear while running down the hwy at 65-70 then maybe... However, if it takes a fair amount of throttle to run at that speed now then I'd say it will take more fuel with the lower numerical rear end.
Although, I'd say for a fact that my 1 ton cummins powered truck would see an increase in MPG. The SD... I don't think so. The TD, definately not, I'll stick with the 3.07.
I think MB had it right off the ass'y line. I don't think we can do much better.
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  #17  
Old 10-28-2009, 01:26 AM
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Quote:
Originally Posted by Whiskeydan View Post
ymmv.

Has a lot to do with the engine tuning. Cam chain enlongation on these old 617s have shifted the torque to an even higher rpm now. Perhaps if if seems like you could use another gear while running down the hwy at 65-70 then maybe... However, if it takes a fair amount of throttle to run at that speed now then I'd say it will take more fuel with the lower numerical rear end.
Although, I'd say for a fact that my 1 ton cummins powered truck would see an increase in MPG. The SD... I don't think so. The TD, definately not, I'll stick with the 3.07.
I think MB had it right off the ass'y line. I don't think we can do much better.
So you are saying that your imagination trumps my real life experience with changing the diff ratio in my benz?
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  #18  
Old 10-28-2009, 01:54 AM
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Originally Posted by Whiskeydan View Post
I think MB had it right off the ass'y line.
Then you better get a 2.88 in your 300SD's.
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  #19  
Old 10-28-2009, 01:57 AM
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what w126 diffs have people put into turbo w123's with what result? what would be the best w126 diff to increase my low-end power on the w123 turbo?
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  #20  
Old 10-28-2009, 02:05 AM
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If you want more acceleration you need a higher number in the gear ratio. Your car is a 300d turbo? If you want more acceleration and your car currently has a 307 diff you would want perhaps a 346. You would gain acceleration but lose economy.

If you wanted better economy you would want to go the other way, perhaps to the 247 diff.

The only way to have both is to get more gears to work with in your tranny.
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  #21  
Old 10-28-2009, 02:16 AM
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Quote:
Originally Posted by t walgamuth View Post
If you want more acceleration you need a higher number in the gear ratio. Your car is a 300d turbo? If you want more acceleration and your car currently has a 307 diff you would want perhaps a 346. You would gain acceleration but lose economy.

If you wanted better economy you would want to go the other way, perhaps to the 247 diff.

The only way to have both is to get more gears to work with in your tranny.
so at what speed and rpm range would i stop feeling the acceleration benefits of a 3:46 diff in a w123 turbo? over a 3:07, that is?
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  #22  
Old 10-28-2009, 07:43 AM
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Well at cruising speed you would have lot more engine noise since it would be turning 20% more rpm on the highway. You'd use about 20% more fuel too....in round numbers.

But the car would feel more peppy at all speeds up til it ran out of rpm.

The top speed would be limited by the governor to about 90-95....instead of over 100.
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  #23  
Old 10-28-2009, 09:21 AM
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Originally Posted by WDBCB20 View Post
What are the symptoms of yours being "shot"?

The first pic in this thread shows the type of wear I am seeing. I'm pretty sure this type of wear classifies it as being "shot".

Excessive W123 Differential Wear - Pictures


This creates a "heavy/dramatic" clunk when putting the car in gear and when down shifting at slower speeds.
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  #24  
Old 10-28-2009, 10:44 AM
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Originally Posted by t walgamuth View Post
So you are saying that your imagination trumps my real life experience with changing the diff ratio in my benz?
Uh... yea.

Do this Tom, next tank of fuel change your driving habits. Start off in 2nd gear, shift to 3rd quickly before the engine nears its peak torque. Do the same 3-4, 4-5th. In addition to the crankcase oil temp rising I'm betting your fuel mileage drops.
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  #25  
Old 10-28-2009, 10:52 AM
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Originally Posted by Les Jenkins View Post
Then you better get a 2.88 in your 300SD's.
I always got better mileage from my 83 SD with it's 3.07 than I do with the 85with the factory 2.88. The 2.88 is fine in the diesel W126, I just wouldn't want a 2.47 for my drive.

But, for those who want to go to the trouble of swapping ratios, speedometers... go ahead. Don't let me stop you. I'll gladly sell you a differential.
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  #26  
Old 10-28-2009, 11:17 AM
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I have a 2.47 out of a gasser in my coupe. I regularly get 31-33MPG in mixed traffic. speedo is off by 40% which make the cruise control function interesting, but otherwise I do the speed calculation in my head. one of these days Im going to pull apart a 300 speedo and see if the gears can be changed to get a better reading, but it doesnt bother me and gives me a smile at the pump.
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  #27  
Old 10-28-2009, 11:47 PM
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how about a 3:58 diff out of a 230e w123, into a turbo w123--would that achieve about the same results as a 3:46? which is preferable if low-end power is desired--the 3:46 out of the diesel or 3:58 out of the gasser?
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  #28  
Old 10-28-2009, 11:54 PM
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The difference between the two is negligible.

If you REALLY want low end power, get a 2.92 out of a 200D or 220D.
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  #29  
Old 10-28-2009, 11:58 PM
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Originally Posted by Les Jenkins View Post
The difference between the two is negligible.

If you REALLY want low end power, get a 2.92 out of a 200D or 220D.
so, it's not correct that if i put a higher ratio diff that I get better low-end power?

what would the 200d/220d 2.92 limit the top speed of a w123 turbo to?
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  #30  
Old 10-29-2009, 12:14 AM
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The larger the number the greater the leverage the engine will have against the wheels.

80mph will be the top speed at 4500rpm.
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