ATF Leak 84 300D

[Bruce Bonds]

84 300D. Several weeks ago, I checked the ATF level and found it low. I added 4 ounces, drove it some and checked it again. I ended up adding 12 ounces. My problem now is that ATF drips from the trans. while the car is running. I spent a long time under the car today, with the engine running to see from where the drips are coming. I was hoping it was a bad pan gasket, as I am about to do a fluid/filter change. No such luck. The drips are coming from above the pan. The ATF is coming from somewhere above the gasket and is at a location between the green modulator valve and the middle pan bolt on the driver side.

I was careful not to overfill. I do not know if the drips are related to the additional fluid, but I never noticed the red ATF spots under the car before this time and I consistently check for fluid leaks.

Anyone have any ideas? Thanks for any replies.

[Mercedes Man]

Your modulator valve o-ring is leaking. The problem is that rubber gets hard after 20+ years. The o-ring costs less than a dollar and is a very easy fix.

[Bruce Bonds]

Thanks Mercedesman. One question though. How do you remove the green modulator valve? It looks like it will be awful hard to get to. Does it screw out? Would you suggest replacing the valve with a new one while I am at it. A new valve is $35.00.

Thanks for your advice.

[Mercedes Man]

First, remove the vacuum hose. Be sure you clean the area around the vacuum unit. You do not want dirt to get into the transmission. Once the dirt is gone, you will see the two bolts that you will need to remove. The bolts hold down the retaining plate. The retaining plate will lift up. With the retaining plate out, you can gently pry the vacuum unit all the way around. Once it is loose, pull it straight out--if necessary, turn it. There is a modulating pressure valve that may or may not come out when you remove the vacuum unit. If it is in the transmission, pull it out. The modulating pressure valve is made of plastic and be sure it not broken.

If you want to replace the vacuum unit, you may go ahead since you have it out. If there is a problem with the unit, your transmission will flare. Also, if you buy a new unit, you will have to adjust it--a trial and error process.

If you want to keep the unit, install the new o-ring on the unit. The measurements of the o-ring from the dealer was 1.34" OD, .932" ID, .102" thick.

To install, place the modulating pressure valve on the vacuum unit and insert it straight into the transmission. Once you get it in the transmission, slip the retaining plate into the unit's slot and bolt it down. Put the vacuum hose on and test drive.

When I did this to my 84 300SD, the unit required an adjustment. The leak affected the shift quality. If your unit was previously not adjusted, I would think your shifts would go back to normal.

It is good you live in Sugar Hill since you can easily visit Mercedes Shop.

[russb]

Read this thread on how to replace/reseal modulator valve.

http://www.peachparts.com/shopforum/showthread.php?threadid=79590