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Changing ATF in BMW 740

My sister traveled from Florida over a month ago and stopped to see us on her way up to see our dad and other family in Ohio. She drives a 97 BMW 740iL with a ZF transmission and about 160k miles on the original fluid. She said she had started noticing shifts were not as smooth and could even be abrupt at times. I had several other maintenance and repair items to attend to on this car, and in addition, we decided to service the transmission as well. “Lifetime fluid” as the manufacturer would like you to believe, is the expected lifetime, somewhere around 150k miles. I prefer to change these sooner, say around 100k miles, especially on the GM units in some BMW’s.

Since she was also planning to come back through here on her way back to Florida, I decided to put the Auto-Rx in there to do some cleaning before servicing it with a fluid flush and new filter. The only way to get fluid into these units is the fill plug on the right side rear. When the engine is started, the fluid level should be right at this plug with the car sitting level. So to get the ARx in there, I had to raise the right side of the car up, leave the engine running, and put the 6 oz in using a squeeze bottle marked in ounces.

When she got back down here a month later, she had driven an additional 1200+ miles, so we were all set to do the ATF flush. Not surprisingly, she mentioned that it seemed to be shifting a lot better already. I raised the vehicle up evenly so it would be level, and then drained and dropped the pan to clean it and change the filter. After the pan was reinstalled, I carefully took the cooler line loose (that returns the cooled fluid back to the transmission), and put a clear plastic sleeve up around the fitting, securing it with a tie strap. Then I directed this sleeve down into the drain pan.

Next, I pumped nearly 4 quarts of Amsoil ATF into the fill hole until it started to drip out there, and put the plug back in. Then my assistant started the engine and held the brake pedal while he shifted slowly through the different gears while in manual mode. The idea here is to push as much new fluid into every hydraulic circuit possible, moving as much of the old fluid out and into the drain pan. When the flow slowed considerably, I hollered to him to shut it off and refilled with approx 2 quarts until overflow this time. We continued with this process for several cycles until the fluid coming down the clear sleeve looked like the fluid I was pumping in. In this case, it took several quarts more than the specified capacity of this unit to accomplish this thorough of a flush (probably the only service it will ever see).

Next, I reconnected the fluid cooler return line back to the transmission and then refilled the unit again. Then he started it up again, ran it through the gears one last time, and then while still running this time, I filled the unit one last time until overflow and then put the plug back in and tightened it this time. DONE! Checked for leaks, took for a test drive and it was shifting like a new one.

These transmissions with no dipstick are more time-consuming and messy to deal with because you have to PUMP the fluid in, 2 quarts at a time, instead of just pouring into a funnel 4 quarts at a time. But the results are worth the effort, and it is possible to keep one of these transmissions running well for a very long time!