Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Vintage Mercedes Forum

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 07-21-2013, 07:55 PM
Registered User
 
Join Date: Feb 2007
Posts: 81
1971 250C 70mph at 4,000rpm?

Having replaced the Zenith carbs with Webers, this car runs great. One thing that remains the same is the feeling that it's reving too high (approx 70mph at 4,000rpm) on the freeway. Is this to be expected from a car with an automatic transmission built for the autobahn, or is it likely 4th gear is not engaging?

Reply With Quote
  #2  
Old 07-21-2013, 09:01 PM
JMela's Avatar
Registered User
 
Join Date: Apr 2003
Location: Minneapolis, MN
Posts: 990
Normal. These cars were geared pretty low and were built to rev high, all day long.

You're most likely starting off in 2nd, again, as is normal.
Reply With Quote
  #3  
Old 07-21-2013, 09:07 PM
Registered User
 
Join Date: May 2012
Location: Orange County/Bozeman
Posts: 199
Yep, normal. You can install a lower ratio diff it it really bothers you. Will lose some around town power but could gain some highway mpg's.
Reply With Quote
  #4  
Old 07-22-2013, 12:00 AM
Registered User
 
Join Date: Feb 2007
Posts: 81
Thanks. I'd like to convert to manual, but in lieu of that I am interested in a lower ratio diff. Any ideas as to what ratio I currently have, might consider changing to, & where to get one?
Reply With Quote
  #5  
Old 07-22-2013, 12:09 AM
Registered User
 
Join Date: May 2012
Location: Orange County/Bozeman
Posts: 199
I think it's a 3.69, and you can swap to a 2.88. I do believe there is one in the classifieds now. And on swapping to a manual, the ratios are nearly identical and 4th is still 1:1. 5 Speeds with an overdrive are priced their weight in gold.
Reply With Quote
  #6  
Old 07-22-2013, 12:10 AM
Registered User
 
Join Date: Feb 2007
Posts: 81
Quote:
Originally Posted by JMela View Post
Normal. These cars were geared pretty low and were built to rev high, all day long.

You're most likely starting off in 2nd, again, as is normal.
Mine seems to go from first to second almost immediately upon forward motion. Not sure I understand how starting in second can be normal. What is first for?
Reply With Quote
  #7  
Old 07-22-2013, 07:18 AM
Registered User
 
Join Date: Jan 2013
Posts: 93
I don't like it either
Lucky for me I rarely go on highway
First gear is when you tough or really steep hill
Reply With Quote
  #8  
Old 07-22-2013, 08:43 AM
JimFreeh's Avatar
Benz addict
 
Join Date: Mar 2007
Location: Hampton Roads, Virginia
Posts: 3,353
Quote:
Originally Posted by JMela View Post
Normal. These cars were geared pretty low and were built to rev high, all day long.

You're most likely starting off in 2nd, again, as is normal.

Nope,

First gear start.
Light throttle will upshift to second quickly.

And, yes, it's spinning merrily along at freeway speeds.
Doesn't seem to bother it any, very smooth.

Jim
__________________
14 E250 BlueTEC black
94 E320 Cabriolet Emerald green
85 300TD 4 spd manual dark blue
Reply With Quote
  #9  
Old 07-22-2013, 09:23 AM
Registered User
 
Join Date: Jan 2012
Location: Leiden, Netherlands
Posts: 611
Quote:
Originally Posted by caviterruptor View Post
Mine seems to go from first to second almost immediately upon forward motion. Not sure I understand how starting in second can be normal. What is first for?
Starting in second was not uncommon on MB automatics, as it would also reduce pulling when the car was stopped at a traffic light. If the transmission would be in first gear, the pulling common to automatics would be higher. The torque converter could deal with second gear start. First gear would only be there when the selector would be in L or when you used kickdown to take off.

Later MB developed systems to shift back to first gear upon take-off. The transmission would stand in second, but shift back to first gear. On some models it required the accelerator pedal to be pressed deeply, on others only a slight touch would produce the shift back. MB used the bowden cable, shift rod or vacuum to shift back, depending on model/engine.
Reply With Quote
  #10  
Old 07-22-2013, 05:02 PM
Registered User
 
Join Date: Feb 2007
Posts: 81
Quote:
Originally Posted by ssk831 View Post
I think it's a 3.69, and you can swap to a 2.88. I do believe there is one in the classifieds now. And on swapping to a manual, the ratios are nearly identical and 4th is still 1:1. 5 Speeds with an overdrive are priced their weight in gold.
Thanks. What classifieds are you referring to?
Reply With Quote
  #11  
Old 07-22-2013, 10:52 PM
Registered User
 
Join Date: May 2012
Location: Orange County/Bozeman
Posts: 199
On this forum in the parts for sale area. Also check Benzworld as they have a strong W123 community and their diffs should work as well.
Reply With Quote
  #12  
Old 07-23-2013, 07:07 AM
JimFreeh's Avatar
Benz addict
 
Join Date: Mar 2007
Location: Hampton Roads, Virginia
Posts: 3,353
Quote:
Originally Posted by Govert View Post
Starting in second was not uncommon on MB automatics, as it would also reduce pulling when the car was stopped at a traffic light. If the transmission would be in first gear, the pulling common to automatics would be higher. The torque converter could deal with second gear start. First gear would only be there when the selector would be in L or when you used kickdown to take off.

Later MB developed systems to shift back to first gear upon take-off. The transmission would stand in second, but shift back to first gear. On some models it required the accelerator pedal to be pressed deeply, on others only a slight touch would produce the shift back. MB used the bowden cable, shift rod or vacuum to shift back, depending on model/engine.
Second gear start is later than the OP's car.
The car in question IS a first gear start car.
It does not have a torque converter, it has a fluid a coupling.

The second gear roll off start you are describing became common in the eighties.

Yes, while standing, the transmission could select second gear to reduce the "pull", but upon any movement, it shifts to first.

Even under light throttle, it will start in first. How quickly it upshifts depends upon the amount of throttle given when accelerating.

I've owned dozens of W114/W115 cars over the last 30+ years, and all of them exhibited first gear start. I didn't experience the second gear start until I bought my first early W124. Late W124s have first gear start.

Jim
__________________
14 E250 BlueTEC black
94 E320 Cabriolet Emerald green
85 300TD 4 spd manual dark blue
Reply With Quote
  #13  
Old 07-23-2013, 04:07 PM
Registered User
 
Join Date: Jan 2012
Location: Leiden, Netherlands
Posts: 611
Quote:
Originally Posted by JimFreeh View Post
Second gear start is later than the OP's car.
The car in question IS a first gear start car.
It does not have a torque converter, it has a fluid a coupling.

The second gear roll off start you are describing became common in the eighties.

Yes, while standing, the transmission could select second gear to reduce the "pull", but upon any movement, it shifts to first.

Even under light throttle, it will start in first. How quickly it upshifts depends upon the amount of throttle given when accelerating.

I've owned dozens of W114/W115 cars over the last 30+ years, and all of them exhibited first gear start. I didn't experience the second gear start until I bought my first early W124. Late W124s have first gear start.

Jim
It is a slightly mixed picture, see the picture below from the Mercedes-Benz Technical Companion:



The W114/115 had indeed a fluid coupling until 1973.

Diesels with a torque converter transmission had a second-gear start. Most 123 petrol cars had second-gear start, diesels got a first-gear start from 1980 and turbodiesels from the start in 1978. High-power models (V8s) had second-gear start.
Reply With Quote
  #14  
Old 07-23-2013, 05:21 PM
Registered User
 
Join Date: Feb 2011
Location: Modesto CA
Posts: 2,966
To return to the OPs opening query, we can begin by calculating engine speed at 70 MPH for the car in question (70 114C), which, if a US spec car will have a final drive ratio of 3.92:1, and tires of 76.5 circumference.

70 MPH = 6160 ft/min

6160/(76.5/12) = 966 wheel RPM, 966x3.92 = 3788 engine RPM

If the car were non-US, with a 3.69 final drive, engine speed would be 3565 RPM

At 4000 RPM, vehicle speed would be 74 MPH, and 79 MPH, for the two final drive ratios respectively.
Reply With Quote
  #15  
Old 07-24-2013, 12:25 AM
Registered User
 
Join Date: Feb 2007
Posts: 81
Quote:
Originally Posted by ssk831 View Post
On this forum in the parts for sale area. Also check Benzworld as they have a strong W123 community and their diffs should work as well.
Still not getting it. Clearly I'm unfamiliar with any classifieds & the only reference to parts I see on this forum is Pelican Parts "New Parts Catalog". Can you be more specific as to how I can access the "parts for sale area" on this forum?

Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 11:42 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page