Automatic transmission flush on Mercedes Benz tranny

Hey guys, trying to change the transmission fluid and filter on a 2004 base carrera with a Mercedes Benz automatic transmission. Having some mixed information from the Porsche tech and some research I found ( mostly from pelican since everywhere else has the older transmission). On the attached picture it shows the blue arrow being the fill plug and red being the drain. However a Porsche tech said the fill plug is located somewhere else between the gear box and the auto tranny and the blue arrow plug is call the control plug where you would open if your transmission is overfilled. To me.. why can't u use the control plug to add fluid? I'm confused as I usually work on BMWs and the fill plug is the "control" plug where that is the level when max. Any help is appreciated. Thanks

The fill port is seen in your upper right photo in the lower right, with the hex shaped cap. When removed, it looks similar to a Schrader valve, but it's simply a hollow, threaded fitting. It is designed so that you can fill/add fluid through that port until it reaches the level of the overflow (blue arrows in your pics) per the Pelican article.

Does this help? https://www.renntech.org/forums/tuto...-transmission/

This is what I use, connected to the hose of a garden sprayer, with modest pressure. The fitting that attaches to the fill port is 14mm (I believe - verify by removing the cap & match to that to be sure. Nothing will leak from there with engine off).

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Thank you for the info. I looked up the diy on there and that transmission shown is different from the Mercedes Benz transmission that is put on the 03+ I believe. That's why it's so confusing.

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Thank you for responding, Just to verify, you referring to the place where I drew a blue circle?

The transmission in the photos in your original post is the same as your transmission (I have the same one -'04 C2). You could theoretically fill through the overflow port, but that opening is really tiny. It really needs to be pushed in through the fill port.

That's it! That's the port you have circled.

I just did this on my 03, it's the same trans as yours. Be careful, somehow filling the trans through that pressurized port caused trans fluid to short out the electrical harness for the trans that's on the top of the transmission. This cause the trans to go into "Emergency mode" and wouldn't shift out of first gear. Had to tow the car to the Porsche dealer where they fixed it for under $300. Mechanic said we did a good job on the filter/fluid change and that the trans oil cooler lines were what leaked onto the electrical connector. I don't buy that 100%, but I haven't had a chance to put the car up on a lift and check it out. When my friend gets back from vacation I plan on checking it out. Hope all goes well for you!

Got a weird question with this exact tranny setup. Recently bought a 996 with this setup. I blame myself and should have checked the tranny fluid and didn't, had a leak on the tranny cooler and I think it got low enough I messed up the TC pump seal and smoked the snout. I dropped the tranny fixed it all. Filled it. Took it to Porsche for them to check (being first time I didn't want to pay their bill for the tranny drop, but I did want them have them look things over and do the proper top off.) NOTE I DIDNT HAVE THE LEAK ANYMORE. I was able to remove the bottom plugs before and watch the fluid leak out of the seal. They said I used the wrong fluid and changed it all out. ( I thought I got the right stuff off pelican) Either way now, after I get it back from them. Every time I start up the car it pushed out 1/8 cup? of fluid out of the TC pump seal. Then is stops, wont do it till I let it rest a day. I think they over filled the tranny. HERE IS MY QUESTION. I take off that top plug (BLUE ARROW) and it comes RUSHING OUT., so I put the plug back in. Yes the car was cold. I am thinking I will do a full start up/warm up and check again. I am thinking that it still has too much in it and when it all drains back out of the tanny, first start up too full?? Then it fills the tranny and its good? Have any of you all seen this before? did I mess up putting the seal in. I don't think i did but maybe.

To check the ATF level, the fluid needs to be between 35-40C (85-10F). You can determine that with an OBD-II reader with that capability or infrared/laser thermometer. In running up to that temperature range, include about thirty seconds at about 2000 RPMs to insure the torque converter is full, and select & hold in each gear for about ten seconds, which will fill the valve bodies, spaces & passages. Leave the engine running and remove the fill port plug. You're looking for a thin stream of fluid to escape and slow to a drip when its full. Add or release fluid as needed to reach that condition. At no time during the process should you shut the engine off. Only do that once you've adjusted the level and replaced the filler plug.

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Well said, that's the way to do it!

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Thank you Mark and Sasilverbullet. I get that, my question is more has anyone seen this before, of TOO FULL and fluid gets pushed out the TC pump seal during start up. I will go do laps in the neighborhood and get the tranny warmed up and then i will check the fluid again.

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What/where is the TC pump seal? I'm a auto trans trained overhauler, so be technical. fyi, I've been toying with the idea of checking/adding fluid via the overflow and not the schrader type valve. Of course checking the temp properly first...haven't done it yet, still debating. The last time I filled my trans using the port after filter change it leaked so much fluid out the top, and that dribbled down to the connector, soaking it, causing it to go into limp mode and require a tow to the dealer to fix.

Thank you for the help So I am talking about the Torque Convertor seal, where when you insert the torque converter snout into the transmission and you get the 2 clunks when setting it. That seal that seals around the snout of the TC. I believe it is a TC pump seal??so when you fire up the car, the tanny pumps fluid out to the TC to make sure it is full? I have my car up on a 4 post, I took out the 2 rubber plugs on the bottom of this mercedes benz trip, i can see that seal and the snout of the TC. When i start the car (after letting cool off and settle all night) when i start the car, it will leak from that seal for a second? or two, just enough to be annoying. IT WILL NOT DO IT AGAIN till i let it rest over night. REVVING it also doesn't let it drip.

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Thank you for the help So I am talking about the Torque Convertor seal, where when you insert the torque converter snout into the transmission and you get the 2 clunks when setting it. That seal that seals around the snout of the TC. I believe it is a TC pump seal??so when you fire up the car, the tanny pumps fluid out to the TC to make sure it is full? I have my car up on a 4 post, I took out the 2 rubber plugs on the bottom of this mercedes benz trip, i can see that seal and the snout of the TC. When i start the car (after letting cool off and settle all night) when i start the car, it will leak from that seal for a second? or two, just enough to be annoying. IT WILL NOT DO IT AGAIN till i let it rest over night. REVVING it also doesn't let it drip.

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Ah, got it! So that doesn't sound like normal behavior. Whether you want to live with it or pull the engine/tranny out (must pull as a unit) is up to you. I live with two minor leaks, the trans oil cooler and around the schrader valve. It makes about a silver dollar sized spot on each over a few days.

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Agreed, yeah i dont think it is normal behavior and it is rather annoying. That is why i keep wondering it is overfilled or a bad seal ( i really don't want to pull again). I also have the small leaks on the oil cooler and the schrader valve but those are like drips versus a 1/8 cup dump each time i start it. (after a day of cool down of course) just be nice that they make it easier to fill or top these units off i was to live with leaks.

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1/8 cup dump each time i start it. YIKES!!! Yes, I'd pull it and fix it...

Turbo -- I see your dilemma, it's not adding up. I'd be less confident of the dealer after they, without asking, replaced fresh fluid simply because it wasn't their brand. I doubt that Pelican gave you "wrong" type of fluid. With that, you could consider the possibility that they overfilled it. Whether or not that could result in some belching out from the front seal is a question for those more familiar with that issue. I agree with Silverbullet that you may ultimately have to yank it to correct it. But, since the problem first surfaced after the dealer fill, you might first approach them with the problem & hope they resolve it. Otherwise, I see no harm in opening the side port (per above procedure) to check the fluid level. If it turns out to be overfull; and correcting that eliminates the leak, then your probably ok. In any event, I would avoid driving it if its overfull, which can be really harmful to the transmission. GLWS.

Trbomofo - did you just change the seal? How bad was the torque converter hub?did you remove the front pump and change the front pump bushing?I currently have a transmission that was low on trans fluid and the front pump bushing seized to the converter hub , and walked in the front pump towards the engine and pushed against the seal causing the seal not to seat against the hub. Just putting that out there.Some times leaks are caused by blocked transmission vent. Hopefully it is just overfilled. Good luck.