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Discussion Starter #1 (Edited)
Hi...I'm new here. I have been reading all of the posts about transmission modulator removal, re-installation, and adjusting, and I am extremely grateful for all the information that is on these forums.

I have a 1983 300TDT (wagon) and this all started because I found ATF in the vacuum lines. So, I removed and replaced the vacuum modulator (green) and pressure tested it. I set it to 48 psi. After setting the pressure, I test drove it and realized that I forgot to hook the vacuum line back up. The car was driving HORRIBLE! I had to floor it to get transmission to engage, and shifting after that was VERY ERRATIC.

When I got back under the car to hook up the vacuum line, hoping that would solve my problem. When I was under there, I noticed the transmission pan gasket was leaking in 2 or 3 spots. UGGG. Does that mean there's too much pressure? Should I just turn it down? Can anyone help me? I haven't tried driving it again, I don't want to cause any permanent damage.
 

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I do not understand the pressure seting that you did.

My understanding is that you use a Pressure Gauge (installed in the approperiat port) set up and set the Modulator Pressure following the Instructions as compared to the amount of Gauge Pressure.
After that then you can tweek the Modulator adjustment a little.

Mercedes-Benz Transmission, Steve Brotherton, ImportCar, February 2002
Transmission Vacuum Adjustment

I have also read that the Plastic (about $7) Modulator Pin often breaks when your remove it.
 

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Discussion Starter #3 (Edited)
Ok, after I installed the modulator, I hooked up a pressure guage to the 12mm bolt to the right of the modulator. Then I started the car and the pressure was at 42psi. For my wagon, I read that I need to have it at 48psi. So I adjusted it up.

Thanks for the tip, but the entire pin came out...luckily.

I am just concerned about the immediate onset of transmission fluid leaking.
 

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Maybe you need a new gasket, change the filter as well.
Are you totally sure is the pan? A new pan is a fairly inexpensive item.
Sometimes is the dipping tube base that leaks. There is a crush washer that goes bad.


However, there is info in the link in my signature.
Mercedes source has a very helpful book about transmission diagnose and adjustment, you can buy a kit that has gauges included.

Good luck
 

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Discussion Starter #5
Ok, I'm really frustrated now. Help!

It's the modulator that is leaking.

I removed it and found the o-ring had been "folded over" when I put it in.

Got a new o-ring, installed the modulator with the new o-ring, and it is still leaking. Any clue as to why it might be leaking? I was sure I got it in right this time, because we ended up just taking the entire transmission out. I was at the perfect angle, put it in straight too.

Also, can you adjust the pressure of the modulator while the car is running? I took the cap off and adjusted the pressure while it was running.

Also, I have a picture of the modulator I received from Autohaus.

The one on the left is the old one, and the one on the right is the new one. See how the new one tapers down more at the bottom. Is this right? Has anyone put one of these modulators in and had success?

Thanks in advance
 

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your new modulator needs to be exactly like the old one as I know. That is probably the wrong one.:eek:

As well as you, I thought I had to replace mine. it wasnt necessary, adjusting the VCV and ATF/FILTER change did the trick

the kit I mentioned before from mercedessource has all the tools, gauges and pictorials you need to do this. It also warns you about things that can go wrong and how to prevent it. If you think about all the time you're gonna save buying that kit is worth more money than they charge for it.

123 126 Diesel Transmission Ultimate Diagnostic and Tuning Kit | MercedesSource.com

This forum is helpful, and we would try to help but we are not there to take decisions and troubleshoot. Believe me I went all over the internet to find out there is no FREE consistent advice, mercedessource diagnose kit is the way to go. I don't know how much I can stress that out, but it will save you headaches like the one you have now.

I wish you were close to Sacramento CA, :bowdown: dieselkraut22 (Garret) is an amazing mechanic specialized in w123s. He would fix it all for an also amazing and affordable price. :thumbsup:

Good luck man, there is lots of free info in the link in my signature.
 

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Discussion Starter #7
Thank you so much! You have given me hope! :)

I just ordered the green modulator from Mercedes Source. I already have the Mercedes 61x Diesel Automatic Transmission Modulating Pressure Test Kit. I think I will order the other items as needed.

I will let you know how putting this new modulator in goes...

So grateful for your response.

Question: I had ATF in my vacuum line. That is how I decided the modulator was bad. Do you think that adjusting the VCV and ATF/FILTER change would have done the trick?

Yah, I wish I was near an affordable mechanic. The shop I called never had the courtesy to call me back. The world needs more honest and affordable mechanics!
 

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Question: I had ATF in my vacuum line. That is how I decided the modulator was bad. Do you think that adjusting the VCV and ATF/FILTER change would have done the trick?

Yah, I wish I was near an affordable mechanic. The shop I called never had the courtesy to call me back. The world needs more honest and affordable mechanics!
Man, its all good, the time will come when you would love to help somebody that's going thru the same situation.

All shops wanted to rebuild my tranny, the cheapest bid was $2500.

The ATF/Filter is something you should do anyways. And after installing the modulator and adjusting its pressure you are gonna have to check your vacuum system also. in my case the Mod was ok, I still have a new one. You are right, if there was ATF in the lines then it was broken.

Good luck!:thumbsup:
 

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Oliveoil, How did you make out with your tranny? I have a 1995 e300d w124 and also replaced the modulator. However I cant get the quality of the system correct. Ihave tried accessing epc Startek but with three different computers and operating systems I am still unable to . I wish they had Mac because that is all I use. Im looking for the Technical bulletin to tell me the way to adjust the tranny hydraulically and what the pressure should be and what tools and banjo size connector I need. Its really driving me crazy.
 
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