Hey Slick, (so cool to write that
< ), what are you expecting to see... gravel? Can you see a 30 micron particle? I admit I can't, though I did see a fairly large pile of ferrous goop on the magnet of my '05 F-150s trans pan magnet when I changed the factory fill ATF at a mere 11K miles. Given that the F150 pan filter is designed to catch 100-150 micron particles, that means a lot of stuff is passing through the system.
I suggest you read the following SAE papers, "Optimizing Automatic Transmission Filtration" 1998 (Eleftherakis & Kahalil), paper number 99PC-418, and "Development of a Laboratory test Contaminant for Transmissions" (same Authors), 1990, paper # 900561.Both are available off the SAE website, $14 at the time I got them. They will open your eyes.
Fluid contamination didn't quite matter as much in the old days, but now, with electronic solenoids, it's more of a problem. What are solenoids? Magnets, and the magnetism can attract ferrous particles to jam valves and, in extreme cases, build up enough material around it to weaken the magnetic field of the valve and cause operational problems even... if it doesn't jam it with debris.
In the 1990 paper, after the authors analyzed thousands of fluid samples, they came up with an "average" mix of contaminants they could use to test transmissions. The idea was to find an average for a high mileage trans and then this mix was applied to a particular trans to test it's reaction to it. It contains particles from 5 to 80 microns, mostly 5 to 10 micron, that was 50.63 percent iron, 11.49 percent aluminum. 20.95 percent copper and 7.19 percent lead.
Frequent changes will alleviate these problems, of course, but often you are tossing perfectly good fluid, save for the slurry of wear particles contained within. My answer has been two things, a Racor 6 micron nominal (about 10um abslute) spin on transmission filter on one of my trucks and a Magnefine inline filter (both are easily found Googling) on the other. The Magnefine is only 35 microns but has a powerful magnet to catch ferrous debris (over 50 of the stuff if you believe Mssrs. Eleftherakis & Kahalil).
The Magnefine is approved by Ford and has passed their qualification tests, as it has with Chrysler, and both companies use them when a trans has failed and is being replaced to catch debris in the coolers and lines ( in both cases, it remarkably lowered the recurrance of failures). The Racor underwent extensive tests in fleet use and extended trans life by orders of magnitude for a fleet of ambulances. Both devices install into the cooler lines, both have bypass capability and neither are a significant flow restriction. I have taken the "before" fluid samples and will get particle analysis done. After I get the filter installed, I will run for a while and then same again and retest. Ding the same thing with the power steering on both trucks (with the Magnefine, which fits into the PS return line).
The Magnefine ridiculously easy to install. The Racor is a little harder but still not too bad. Main problem is finding the room to mount the Racor filter base bracket under the truck.
One incidental thing I learned was that magnetic fields weaken with heat, so the pan magnet (or drain plug magnet) is releasing material when the fluid gets hot. When I asked Magnefine about this, they agreed, but said their magnet is a particularly strong one and that the way the fluid is routed around it compensated for whatever magnetism was lost. In looking at a cut open unit, I'd have to agree.
BTW, I will share this stuff on BITOG, but it has to go into a magazine story first.