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  #1  
Old 01-09-2009, 12:07 AM
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help me understand shift points please

I don't drive on the highway very often, but I noticed that my 300d seems a little more strained than usual above 70 mph recently, but it's probably my imagination. Just want to understand this better and make sure everything is kosher.

There are shift point dots on the speedometer: 24, 40, 65 mph and another one ridiculously high. As far as I can tell, my car starts in 2nd, shifts to 3rd around 24 mph, then to 4th around 40 mph, then no more shifting. It all feels right until I get to that shift point at 65 and it doesn't shift. Does this seem right? I don't have a tachometer, so I can't judge things that way.

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  #2  
Old 01-09-2009, 12:12 AM
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Quote:
Originally Posted by kenstfelix View Post
There are shift point dots on the speedometer: 24, 40, 65 mph and another one ridiculously high.
Those are not shift points. They are the maximum allowed speeds in the respective gears if you are selecting those gears manually.
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  #3  
Old 01-09-2009, 12:19 AM
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You know i too want to know what is there a ONE dot at around 90 MPH... I used to own a 1978 300D and that one dot at 90 MPH always puzzles me, Max Speed that the car can go before the engine gets damage or (redlining???)
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  #4  
Old 01-09-2009, 10:02 AM
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I've been pondering shift points lately as well. Did a search and can't find info regarding an explanation for uneven shift point RPM's for different gears. i.e. on my '85 300D full throttle 1-2 shifts at 3000rpm, and then keeping it floored the 2-3shift holds much longer and doesn't shift until 4500rpm or even a bit more which too my ears sounds too high.

Is there anyway to adjust the shift point from gear to gear, or is this just indicative of an old tranny (231k miles on mine......though maybe PO had it rebuilt?).

Another good question: are there any good telltale signs to look for to determine if motors or trans have ever been rebuilt?
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  #5  
Old 01-09-2009, 10:18 AM
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4500 or higher is in my opinion exactly where it should be shifting at WOT
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  #6  
Old 01-09-2009, 10:48 AM
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I did a test on my 300SD, i tested the shift points by just holding the gear selector until the speedo reachs to each dot, and it seems when the speedo needle points to the dots the rpm is at 4500, maybe it could be the the peak horse power for each gear... after all, 4500 RPM is the peak horse power for all OM617, worng correct me if i am worng...
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Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi
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  #7  
Old 01-09-2009, 10:52 AM
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a tachometer would be nice....
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  #8  
Old 01-09-2009, 11:28 AM
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Quote:
Originally Posted by Actros617 View Post
I did a test on my 300SD, i tested the shift points by just holding the gear selector until the speedo reachs to each dot, and it seems when the speedo needle points to the dots the rpm is at 4500, maybe it could be the the peak horse power for each gear... after all, 4500 RPM is the peak horse power for all OM617, worng correct me if i am worng...

I think you may be wrong - search "dyno results" / "dyno chart"
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  #9  
Old 01-09-2009, 11:58 AM
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Quote:
Originally Posted by Actros617 View Post
I did a test on my 300SD, i tested the shift points by just holding the gear selector until the speedo reachs to each dot, and it seems when the speedo needle points to the dots the rpm is at 4500, maybe it could be the the peak horse power for each gear... after all, 4500 RPM is the peak horse power for all OM617, worng correct me if i am worng...
You are correct. The peak hp is approx. 4400 rpm for the 617.
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  #10  
Old 01-09-2009, 12:23 PM
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Originally Posted by jt20 View Post
I think you may be wrong - search "dyno results" / "dyno chart"

my bad.

TORQUE - the more significant of the two - reaches a maximum at a much earlier rpm
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  #11  
Old 01-09-2009, 12:46 PM
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Originally Posted by jt20 View Post
TORQUE - the more significant of the two -
That would depend on your use of the vehicle. If you intend to race it for the fastest 1/4 mile times, horsepower is your number.
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  #12  
Old 01-09-2009, 12:56 PM
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Mine is adjusted so that it won't go much over 4100 in 2nd and maybe 4200 in third....but in 4th it will pull to the end of its power range. (around 105-110mph)

I adjusted it that way on purpose....keeps the rev's down a bit since there's not much coming at 4500 anyway.

Now the 300D....it will rev to almost 5000 in both 2nd AND third! Its a stronger motor though....it is fast!!
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  #13  
Old 01-09-2009, 02:36 PM
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But reving it at 3-4 or even 5k rpm, you wont be getting the torque... So do you adjust the bowen cable or the T key under the tranny for the tranny to shift later...
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Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi
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  #14  
Old 01-09-2009, 02:41 PM
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Originally Posted by Actros617 View Post
But reving it at 3-4 or even 5k rpm, you wont be getting the torque...
Like most on the forum, the difference between horsepower and torque is elusive to you.

Horsepower indicates the maximum torque to the pavement that can be provided when the transmission is properly utilized.

The peak torque of the engine means nothing unless you've got no transmission and the engine output torque becomes the torque to the pavement.
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  #15  
Old 01-13-2009, 04:37 AM
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Originally Posted by Brian Carlton View Post
Like most on the forum, the difference between horsepower and torque is elusive to you.

Horsepower indicates the maximum torque to the pavement that can be provided when the transmission is properly utilized.

The peak torque of the engine means nothing unless you've got no transmission and the engine output torque becomes the torque to the pavement.

now that we're on the same page again...


transmissions and all related gearing are based on the engines torque curve. It is the most efficient means of harnessing / creating power. Where 'Power' is the rate of doing work. Torque is the force that allows us to do work over time.

simply b/c the "engine's" HP peaks beyond the torque range only signifies that speed it is spinning has comparatively surpassed the force created by the peak torque. In other words, an equation with hp as a function of engine speed vs. hp as a function of force (torque) favors speed only because the domain of speed is greater for an engine.

Now.. if you were to say "..a car's HP is more important than torque..." we could do this again.

(this is how I justify NOT doing my homework)

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