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Old 09-20-2012, 09:44 AM
bimmerfan52 bimmerfan52 is offline
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Location: Arizona
Join Date: Feb 2012
Posts: 788
Mein Auto: 545i
Originally Posted by kskane View Post
Will work on the trans housing temperature. But while I am preparing my mind for the trans oil change myself, I have a question below in case you might know the answer;
1. Is the trans sump has to be changed every time drain/fill is to be performed?
2. While doing a drain/fill, can the filling start at cold (meaning on cold start conditions). Or the trans has to be on a certain temperature to drain it and then on certain temperature to fill it. And then on between 30-40 C to do the second fill with car running.
3. While doing a drain/fill, the second top up has to be done with car running and in Park with handbreak or car turned off after running.
If you have no record of the ATF having been replaced recently you will want to do it anyway, independent of the shift lock problem.

For further details follow that DIY I posted previously.

1. If the sump is in good condition and has been replaced recently you don't need to replace it again. The filter is integral to the sump which is why it is replaced. (My pan was replaced 12K ago so no need to do the filter, but I believe they reused the old fluid which is why I replaced it recently.) You will definitely want to do the sealing sleeve as long as you are in there.

2. Initial fill can be done cold after drain is finished and drain plug replaced. This makes working under the car much more pleasant.

3. Car must be running for second part of the fill and left running until the 40C temp is reached and the fill hole capped.

Do a very short drive (1/4 km) before draining just to stir the fluid up and temporarily suspend contaminants in the fluid. If you get it too hot you will burn yourself on either the fluid or exhaust pipes or have to wait an extended period for it to cool down at which time the suspended contaminants will have settled again. About 6 qts should drain out - give it an hour or two to drain. Some do overnight in which case more fluid will drain. You will want to measure how much drained so you have a rough idea of how much you will put back in. Make sure you have enough fluid before you begin.

The fill is two part - Initial fill with engine off, then finishing fill with engine on.

Starting the engine has two purposes. First is as the transmission starts to run fluid is sucked from the sump into the torque converter. This drop in the level in sump allows more fluid to be added. Second it begins to heat the fluid to the proper temperature.

Speed is of the essence here. If you have a helper to start the car and stir the gears so you can concentrate on the fill all the better. If you are slow on the draw the trans will get too hot and you will have to cap the fill plug and start over.

Do the initial fill with the engine off until fluid dribbles out the fill hole. Then start the engine.

Then add more fluid immediately after starting the engine until it again starts to drip out of the fill hole. (If you were to turn off the engine at this point with the fill plug out fluid will gush out of the fill hole as the torque converter releases fluid.)

Quickly run the transmission carefully through the gears to insure fluid reaches all parts of the transmission, then go back quickly and observe fluid coming out of the fill hole. If it has stopped, add more fluid immediately until it begins streaming out again.

Now get out your thermometer (I bought a cheap probe thermometer at the auto store) and begin monitoring the fluid temperature in the trans. Fluid should be slowly streaming out of the fill hole the entire time (as fluid temp rises so will the fluid level in the sump). When you get to 40degC install the fill cap finger tight and turn off the engine immediately.

Then wait for everything to cool down before torquing fasteners and reinstalling everything. You may want to take it for a short test drive with the belly pan off so you can inspect for leaks (especially if you replace the pan).

ZF's reasoning behind reaching the specified temperature is three fold. First it forces the mechanic to not forget to start the engine. If the engine is not started after the initial fill the transmission will be drastically short filled.

Second, ambient temperatures vary greatly. If a guy is working in a pole barn in Alaska at -30C you want to make sure the fluid has reached at least a temperature that it is viscous and totally fills the torque converter and transmission before measuring the level.

The third reason is that the trans fluid (like most substances) experiences an expansion as it is heated. ZF designed the location of the fill hole and the temperature range (safe for mechanic at 40degC) such that the fill level is correct when fluid streams slowly at 40C. The temperature spec is not the end of the world if it is off a degree or two. That is why you are given a window to hit. The fluid rises several hundredths of an inch per degree increase of fluid temperature.

Once you go on your drive the fluid will reach operating temperature and the level will rise even more as the fluid expands further at a higher temperature. Then when you turn the engine off fluid is released and the level in the sump really rises far above the fill hole, but the sump/trans assembly is designed to have room for the fluid.

ZF went away from the filler tube and dip stick because so many people were overfilling. Under-filling is still possible if you don't start the engine after the first fill. Overfilling slightly is still possible if fluid is running out of the fill plug and you cap if before you reach 40C but it won't be by much.

I did my drain and fill in the summer in Phoenix when the ambient temperature was 105F. Needless to say it didn't take long to reach 40C so I had to move fast.
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