PeachParts Mercedes-Benz Forum - View Single Post - newbie problems changing tranny fluid on '81 300D

Richard Eldridge · #3 06-14-2004, 12:58 PM

My 85 has a drain plug, toward the rear, I think on the left.

The way to drain the automatic transmission is to take off the oil pan. Replace the gasket and the filter before refilling.

The drain for the torque converter is accessible only after you take the pan off. The TC spins around, so unless you are incredibly lucky, you need to hook up a starter button to "bump" the engine until the converter drain plug lines up with the gap in the transmission you need to get to to access it. I needed to "bump" mine about 17 times. Do this with the ignition key off (or out of the ignition). You don't want it to start, because to shut it off, you would need to drag yourself out from under the car. I would prefer not to be under a running car, especially if I did not have an assistant, which is usual for me.

Use good solid jackstands or ramps, with a chock block behind the real wheels. Do not forget to remove them when you are done. I drove mine up on ramps, then jacked up[ the rear and put it on jackstands, so the car would be level, and not be capable of rolling backward. My foolish neighbor was injured while under a car on a bumper jack, and was slightly squished, which made him walk funny for several months.

You will need: a transmission pan gasket, a transmission filter, 6 to 8 qts of auto tranny fluid (I suggest Mobil-1 synthetic: it should outlast the regular stuff, and being as it is in a cool tranny instead of a hot engine, you won't need to change it for 30K or so, so the higher price is, I think, justified.) You will need a pan or large bucket. I put a tarp under the area, so as to keep oil off the patio/ floor/grass/dirt. You can hose it down if it drools a little. If you wear some rubber nitrile gloves, you will not get your hands dirty.

You will need a socket and socket wrench to remove the torque converter drain plug. I seem to recall it was a 13mm bolt. There are many bolts holding the pan on, and a socket is ideal for this. After you have backed all the bolts as far as they will go, remove the three bolts on the lowest corner and then pry the pan downwards with a tool with a wide flat blade, a putty knife or screwdriver. The oil will flow out of that corner, gradually loosen the other bolts until the oil has all drained out. The idea is to not have it all splatter all over you. There will be a small amount of residue in the pan, wipe it clean. Plastic bits are a bad sign. Make sure it's really clean and free of lint before you replace it.

See the book and make sure of the amount needed by your tranny. The manual for my 85 says 6.6 for a refill every 30K and 7.7 initially. Just put in 5 qts., then top it up as required. It is far easier to put it in than to take it out, particularly if yours doesn't have a drain plug.

Put a small band of blue locktite (the soft stuff) on the pan and the top of the gasket and the top of the gasket. You want just enough to seal, with a very small amount oozing out after it's all tightened down.

Tighten the bolts until the gasket and pan make light contact with the transmission, then tighten every other bolt about a quarter turn at a time, so each bolt will be equally tight. A torque wrench would help, but I don't have the torque specs available.

Check the fluid every 50 miles or so. I had to tighten my bolts a bit after I spotted a couple of drops dripping out.

My transmission shifted more smoothly after the change.

Good luck!