I own a 1990 300e w124 with 256,000 miles. A couple of months ago I let a mechanic friend change the fluid and filter on my transmission. Shortly thereafter I began to have problems (prior to fluid/filter change there were no problems). At first I began to have erratic shifting, now the car will not go into high gear, just revs freely. Any input would be appreciated. Seems to be a lot of discussion on the modulator (hope its that simple). I dont see any leaks but now fluid is disappearing. No blame to the mechanic as he more than competent for this simple job (tightened to spec in star pattern). I was told to leave that fluid alone and sure enough I see on the forum that this problem happens after fluid changes. Introduced gremlins in tranny when it was opened i guess.

Been there, done that with about the same mileage on same model car. First make sure transmission level is correct and find out what kind of fluid was put in it. If everything is where it is supposed to be then it is time to start looking around for a transmission.

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Jim

Did he drain and fill or "flush" it? Did he use Dex III fluid?

If fluid is disappearing then the modulator is sucking trans fluid into intake manifold. Fix that first.

Also, where are you located?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Normally clouds of whitish smoke from the exhaust announce this modulator problem.

Common for 722.3 or 722.4 to start slipping after a fluid change.
Unfortunately rebuild or known good second hand transmission is the ultimate solution.

I just drained and filled the transmission (with filter change) with dex III. I live in the deep south coastal mississippi. Like I said the transmission was all fine until the fluid/filter change.

It just might be overfilled check the level again this transmission is sensitive for overfilling.

I had this happen to me twice, the first time was with my 1986 300E that I had the fluid changed in, shortly afterwards, it began to act up and finally would randomly shift out of gear all the time and it came to the point that the transmission was gone and needed to be replaced.

The second time was in my 91 300E that I currently have, I had the fluid changed which I was very very weary about doing because of the experience mentioned above. Fluid was changed and all seemed well until the exact same thing happened to me and I was really bummed, talked to the mechanic and he told me to wait it out, that the transmission just needed to "adjust" to the thinner clean fluid and it needed to break in. So I drove it, with occasional acting ups it would do until finally it stopped acting up and starting operating normally. To this day, I haven't had any problems and it shifts normally.

Hopefully your transmission just needs to adjust to the fluid as mine had to, but I mean if it keeps doing it for a really long time, it might be time to have work done to the transmission, which sucks. Hopefully it's the "break in" period!

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2007 BMW 328XI

When install the filter never loosen the philips screws as the cork gasket on the filter is a one time crush.

When refilling - fill about 3 qts of fluid and leave it alone for about 10 minutes, the filter will saturate with it. Or it may blow out. The first filter I removed from my trans had mangled up paper. I opened it up (tuff job) and found it blown apart. A mechanic told me that this happens when a flush machine is used with a new paper type filter immediately.

Lastly (not to sound really bad) your trans maybe requiring a rebuild.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

happy to report that my transmission is working fine now. its been a month since i experienced the slipping problem, guess it just needed to get used to the the viscosity of the new fluid. dont know what else it could be. but all is fine now.

That is good to hear.

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Jim