I just completed a comprehensive transmission servicing program on my 1989 740 GL 8 valve. I purchased this neglected brick several months ago with all fluids being dirty to very dirty including the transmission. Mileage 133K

This is a long post including the details of my experience as well as my opinions.

At first I just drained about a quart and a half from the drain pan and refilled with Dextron 3 ATF. This had no visible effect on the fluid as it still looked and smelled like spent ATF. After reading the highly useful FAQ's I knew to drain the torque convertor by disconnecting the line at the top of the radiator, fitting drain tubes, starting the car, and draining as I refilled as described later in this post. After doing this and refilling ~ 8 more quarts of cheap Chevron ATF and also using 4 oz of Auto RX (an additive with excellent online reviews useful for cleaning and possibly fixing any seal leaks on either the trans and engine)

http://auto-rx.com/


I drove the car about 1500 miles before a second service to include changing the trans filter, it's two gasgets, and a new pan gasget. I thought this should take me an hour and a half. I have access to a very well equipted shop with air tools and very nice quality hand tools and manual jacks / stands. It ended up taking over 5 hours and was not easy. I think I am fairly proficient but this was my first time...

Breaking the dipstick connection free at the junction at the transmission pan proved impossible even with large cresent wrench and 24mm open end wrench (and copious amounts of PB Blaster). I live in Hawaii - corrosion was not the issue - this fitting is tight. The amount of force needed would have most likely destroyed the pan. It may have been easier if the car was on a hydraulic lift and one could stand underneath for a better mechanical advantage. I put my foot on the 24mm wrench and could see the pan flexing even though I was preventing the connector nut from turning with a large crescent wrench.

Plan B was to remove the dipstick in its entirety still attached to the pan by removing the two 19 mm bolts that mount the starter to the transmission and also serve as mounts for the dipstick filler tube. The top bolt is almost a blind removal and very difficult to access or break loose from under the car however that is how I did it. Removing the pan with an air wrench is easy. You will need a 10mm 6 point deep well socket. Without this it would take forever.

The pan did have a fair amount of fine metallic dust that formed a layer and also coated two small ~ 1/2 inch square magnets that were on the bottom of the pan.
I used several rags to wipe the surfaces clean as well as some gasoline to clean everything.

There are ~ 7 1.5" bolts holding the trans filter on with a gasget on either side of a build in spacer. You will need an 8 mm 6 point socket and preferably a 1/4 drive rachet to remove them. Once the filter and spacer is removed a copious amount of additional ATF comes out so have a drain pan underneath. The old filter gasgets were wasted - cleaning the mating surfaces of the old gasget material was a major pain. Ended up using a wire wheel on a bench grinder as scrapers and single edged razor blades were not adequate. The wire wheel was absolutely necessary to get the old gasget material off. I used throttle body aerosol to clean and reuse the filter which did have some very fine crud on the screen
possibly enough to restrict flow although I never had experienced any problem.


Putting everything back together is straight forward hampered only by the difficulty of getting those filter bolts through the filter, gasget, spacer and second gasget while you hold all of this in place. I used high temp RTV silicone on the pan to hold its gasget in place and to provide a better sealing surface. I did not bother with spefific torques for replacement and just snugged them in a criss cross pattern on both the filter and pan.

Then I put two quarts of Chevron ATF in the pan and removed the 15mm connector line at the top of the radiator. No clamp is necessary if your hose fits well (get a 5' piece of old 3/8 garden hose) and in fact would be a hindrance for quick removal. There is not much pressure so the clamp in overkill. I started the engine and drained the fluid into clear plastic gallon jugs that I put inside of a 5 gallon bucket. The fluid that came out was not red at all and was quite filthy.

Started adding the Mobil 1 at this point and added 8.5 quarts in total until I was positive that all the old fluid was flushed through and what was coming out was bright red. This wastes several quarts of new fluid most of which was hopefully the cheap Chevron ATF.

Replaced the transmission line and made sure to move the shifter throught the gears a dozen or more times as suggested in the FAQ. Checked the fluid levels carefully several times and went for a test drive.

Shifting is noticeably smoother now and I know this transmission has had a through and comprehensive cleaning and servicing. I read that Mobil 1 ATF can decrease the transmission temp by up to 20 degrees F. So using this expensive synthetic fluid is a major upgrade for ones transmission. It cost me around $90 to do this service myself. I consider it cheap insurance for an auto transmission problem that I have most likely prevented on an old negleced brick that is now in very good condition.

It was worth it but I would say the job is too difficult for most back yard mechanics if dropping the pan and cleaning / sevicing the filter is included unless you have air tools and a well equipted shop.

In retrospect the additional time and toil associated with trans filter servicing is probably unnecessay unless ones car has been neglected as evidenced by filty ATF fluid with its unpleasant stink or a leaky pan gasget. For most reasonably maintained vehicles simply flushing is much much easier, in fact easier than a basic oil change. Hope this clarifies the procedure and provides rational as to which level of tranmission service your brick may need.