Changing Manual Transmission Fluid

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Need: 2 quarts of Valvoline Dexron III Automatic Transmission Fluid (ATF)

Tools required: 14mm Allen wrench
Jack and Jack Stands
grease gun with flexible hose
pan to catch stray fluid

Time it took me: 1.5 hours

Approx parts cost: $50

Yes, the Mercedes service manual for the 240D specifies using ATF for our manual transmissions. Go figure.



The fluid in your gearbox helps keep the gears and synchros cooled and lubricated sufficiently. It does not have to be changed anywhere near as frequently as the engine oil, but in my 1982 240D with 320,000 miles, changing it helped my car. The transmission is now quieter, and the new fluid eliminated a quirk my transmission had: when moving the shifter from left center (gears 1 and 2) to right center (gears 3 and 4), it would have a little resistance near the middle and make a loud "click". Now it springs back to right center if I let it go, just like it should. No click, no resistance. You would be surprised at what routine maintenance does for a car.

1. You will want to jack up the front of your car and use jack stands. You will need the room when you get under the car. The manual gearbox we want to get to is directly behind the jack stand in the picture.


2. This is the gearbox.


Of importance are the two plugs visible in the picture: the one on the left is the filler plug. The one on the bottom of the transmission is the drain plug. The filler plug covers a hole you will eventually be putting the new fluid into. The drain plug is, guess what, used to drain the existing fluid out. The existing fluid level will probably be just below the bottom of the opening of the filler plug.

3. BEFORE you drain out the existing fluid, you want to make sure you can unscrew the filler plug first! Your filler plug may be sealed on tight; this happens over time. If you can't open it to put the new fluid in and you unscrew the drain plug, you've got an empty gearbox and are up shit creek. I could not get mine to budge by hand. You might have to get creative in order to get it loose. I could not fit a breaker bar onto my Allen wrench because of space constraints, so I ended up applying turning force using my hydraulic lever-operated jack. That worked for me.

4. Next, unscrew the drain plug, and let the fluid drain out. About 2 quarts should come out, a little bit less. That's fine. Once it's finished draining, put the drain plug back in.

5. Now you want to use the grease gun to fill the transmission with the new ATF. Keep filling until it dribbles out the fill hole.

6. Screw the filler plug back on; make sure both plugs are screwed on tight.

Enjoy your newly found smoother shifting!

by Daniel Goldman