300sl transmission 4th gear shift? - Mercedes-Benz Forum
 
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#1 (permalink) Old 01-22-2013, 12:46 PM
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300sl transmission 4th gear shift?

1993 300sl 24V with 117K miles. Corrected all the items on my "fix list" except one - the transmission.

Symptoms: Transmission shifts hard, and 3rd to 4th-5th at weird shift points.

Accelerate under normal speed, starting in 1st, 1st - 2nd shift happens around 2200RPM, 2nd-3rd shift around 2200RPM, crisp and normal. 3rd runs up to around 4600RPM, hits 4th, and drops to 5th in another millisecond or so. Sort of misses 4th. Under harder acceleration, there is a bit of a "flair" on the 4th gear shift, then it goes into overdrive 5th. If I accelerate from 3rd to around 2500 RPM, and drop off the gas pedal for a second to decellerate, it shifts into 4th, then shifts to 5th. Still not quite normally, but with less wear and tear.

It's a 20 year old car, so I've been replacing all the rubber vacuum line connectors on the intake manifold, at the vacuum modulators in the electronics box at the upper passenger side firewall, and actually replaced the vacuum modulator and rubber connection on the transmission itself. Shifting has become smoother from the original set of symptoms, and engine runs smoother, but it still isn't shifting correctly. I replaced the transmission filter, filled with new fluid, and replaced the 1st gear shifting control plunger/spring per MB maintenance recommendation. No discoloration in the fluid, no "burned" smell to the fluid. None of these has solved the shift point problem.

Some internet searches suggest that the shifting point problem suggests that the transmission controller is the fault. Using my MB diagnostic analyzer (i.e. the pushbutton thingy) no "flashing lights" seem to be set when I look for diagnostic codes.

I'm running out of cheap fix options!

Before I spend $1200 on a transmission controller, has anyone else experienced these same transmission symptoms? How did you fix it?
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#2 (permalink) Old 01-22-2013, 02:44 PM
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Hi Lee:

On your 1993 300SL, with 5-speed Electronic automatic Transmission Control (ETC), your model has the 16-pin diagnostic connector.

The ETC diagnostics are read from PIN # 13.

If the ETC is functioning properly, you should be getting "1 FLASH".

Just to be sure you are using the proper chart it is:

Electronic Transmission Control 5-speed (722.5)
Models 129, 140
Model Years 1990-1996

Fault Code Table

DTC.... Possible Cause of Failure

1...... No fault found
2.......Engine control module (N3/4) does not match TCM
3.......
Transmission overload protection switch 4th/5th gear defective
4.......CAN data line from EA/CC/ISC control module (N4/1) signal distorted
5...... CAN data line from DI control module (N1/3) or HFM control module signal distorted
6...... CAN data line signal distorted, Short or open circuit
7...... Control valve block (Y3/1y2), open circuit or TCM (N15/1) defective
8...... Automatic Transmission Control Module (TCM) (N15/1) defective
9...... Control valve block (Y3/1y2)
10.... Control valve block (Y3/1y2), short circuit


Please re-test, using PIN # 13, and determine the CODE(s). Then get back to us, and the Forum members will go from there.

God Bless, Arctic
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#3 (permalink) Old 01-22-2013, 03:56 PM
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Green to pin 1, white to pin 3. Black to pin 13. Dull red steady glow. If I push the button for a couple of seconds, I get a bright glow. No flashes.

Think I screwed this up. I went back and double checked. Green to pin 1 is ok. White needed to go in pin 16, so I moved it. Black in pin 13. Now there is no light, nothing when I press the button for a couple of seconds. No light at all

If I hooked it up correctly the second time I would think something is wrong with the mercedes flasher I have.

Advice?
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#4 (permalink) Old 01-22-2013, 05:15 PM
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Good Evening, Lee:

Thank you for your reply.

Okay, you may wish to revisit the Code Reader, itself, and how to properly use it.

Here is a link to a good thread that explains most of the basics: http://www.benzworld.org/forums/r129...my90-95-a.html

Once you have the Code Reader correctly set up, make sure you turn ON the Ignition to Position 2, (ignition ON, without the engine running).

Then do your Code Reading.

If the ETC gives 1 FLASH.... all is well.
If the Automatic Transmission Control module (ATC) is faulty, you should get 8 FLASHES.

Hang in there, Lee, you'll eventually conquer this, and then your ability to diagnose will take a tremendous leap forward.

Once you have things working, and the Code(s) read, then get back to us.

Hope this helps.

God Bless, Arctic
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#5 (permalink) Old 01-22-2013, 05:43 PM
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I had weird tranny happenings last year on my 300SL just when commencing the Newfoundland trip. No 4th gear, shifted right from 3rd to 5th and power was a bit weak too.
Culprit turned out to be a defective OVP relay. Go figure.

91 300SL with Pano Top, 04 S500
formerly 1980 450SL, 1990 560SEL
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#6 (permalink) Old 01-23-2013, 02:49 PM
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One flash. Turned out I shorted with my flasher and blew a fuse. Replaced all my old fuses and retested. One flash

Sort of eliminates the controller and the solenoid coil

Ideas?
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#7 (permalink) Old 01-23-2013, 02:51 PM
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Which relay is the ovp? What does it control?
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#8 (permalink) Old 01-23-2013, 06:18 PM
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Good Evening, Lee:

Way To Go in getting your Code Reader working properly!

It must feel good that you have now discovered you don't need to fork out big $$$ for a new ATC module.

Okay, so as to what may be causing the shifting issue? I don't have a definitive answer for you, at the moment, but I will think about this for the next day or so for you.

Now, in "mrelbe's" post to you, he advised, that for his SL, it was the OVP relay.

Here is a link to a good thread on this for you: http://www.benzworld.org/forums/r129...990-sl500.html

Check out the OVP, and see if this may be the cause.

Hope this helps.

God Bless, Arctic
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#9 (permalink) Old 01-24-2013, 05:06 AM
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In my case the OVP relay fuses tested and looked good. I then removed the cover and found that the problem was the receiver/socket for the fuse blades was loose and the fuse was not making contact.

91 300SL with Pano Top, 04 S500
formerly 1980 450SL, 1990 560SEL
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#10 (permalink) Old 01-24-2013, 05:49 PM
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Good Evening, Lee:

Okay, having pondered your transmission issues, and your having eliminated the ATC module, AND the vacuum modulators as the culprits, I am tending toward the BOWDEN CABLE, at this point.

While I am not familiar with the 5-speed A.T. on a 1993 300SL, it seems to me that your transmission is quite sensitive to small variations in your accelerator pedal position.

There are 5 pages of discussion on adjusting the Bowden Cable at this thread; here is the link: http://www.benzworld.org/forums/r129...-photos-4.html

I am also attaching a PDF on adjusting the Bowden Cable as well.

Hope this leads to success.

God Bless, Arctic
Attached Files
File Type: pdf Pages from 90 R129 intro 1.pdf (202.5 KB, 89 views)
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