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Thread: Transmission Fluid
10-15-2009 06:03 PM #1
My 99 740i has 115k miles. I have not serviced the tranny.
My retired BMW tech (works from home) does not want to do anything
other than check the fluid level. He is afraid something will go
wrong if he disturbs the filter etc.
Does anyone have a contact in North Carolina or the Atlanta area
who could do this (and do it well).
10-16-2009 10:35 AM #2
Re: Transmission Fluid
I'm going to tell you the same thing your retired mechanic probably told you.....
Automatic transmissions are funny. They usually don't like having their fluid changed at 100k miles unless you did it at 50k also.
The friction material of the clutches and shift bands wears off and actually changes the fluid over time-- even though the filter cleans out the particles larger than a few microns. The fluid also begins to break down with heat (and cold) and suspended moisture.
If you change the fluid regularly the suspend particles don't wear the friction parts. If you DON'T ever change the fluid, the suspended particles begin to supplement the worn friction parts. Changing the fluid for the first time on a worn transmission (120k) can actually hasten failure. The new fluid is slicker making the clutch plates work harder and wear faster. And may be more or less viscous, making the valves open and close differently.
I've been a GM guy forever. A THM400 is the workhorse that racers and four wheelers love to abuse. If the fluid is changed every 30-50k they last about 200k. If the fluid and filter are never changed they last about 150k.
The A5S-440 in your E38 is better built than the THM400. Unless the fluid has changed colors (meaning it has overheated or collected huge amounts of water) leave it alone. Unless it is shifting funny (hard or exceptionally soft) just keep the fluid full. The system is a closed loop and unlike engine oil has very few added contaminants; so, the filter will last longer than the fluid.
Plan on spending $2000 to have it rebuilt at about 250k. Or start looking for a re-manufactured ($4000 and up plus installation). Rebuilding replaces the worn parts -- clutches (friction and steel plates), bands, gaskets, and some valves. Re-manufactured makes the trans like new with new parts anywhere they can be replaced.
For the rebuild, check around and see if there is a performance tranny shop in your neighborhood. The chain stores are often training grounds for future mechanics. You might get a master. You might get a retarded apprentice. The boutique tranny shop hires the best and pays them more for better work. (usually. Get references)
10-16-2009 08:59 PM #3
10-17-2009 01:16 AM #4
10-20-2009 10:07 PM #5
10-28-2009 04:56 PM #6
11-16-2009 11:49 PM #7
- Framingham, MA, United StatesMember No: 47455
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- Aug 2002
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Transmission Fluid Change
I changed the fluid and filter of my 98 740 at 111,000 miles. 20,000 miles later it runs fine. Here's what I learned from experience and tranny experts like Kirt Koeller. When transmissions had mineral based oil it caused problems to change it after many miles. The oil formed varnish and sludge which the detergent in fresh oil loosened, causing leaks at seals that were gummed up and sending the dirt into the gears. Modern synthetic fluid doesn't form varnish. I used Esso LT even though newer products are probably better. After a while the tranny made a few clumsy shifts and I got worried. Kirt explained that with fresh fluid of a different viscosity the electronic adaptive controller needed to re-learn how long it needed to allow for shifts. He was right. After a few weeks the problem went away and has never returned. How cool is that? Friction grit left in the old oil that can't be completely drained helps the clutches work after the fluid change. Use a Filtran filter. I got 7 quarts of fresh oil in when i did the filter, and about 4 more when I drained and refilled it again a few days later.
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