Again, the same arguments about tranny flushes vs dropping the pan an changing the filter.
The transmission filter does not serve the same function as the engin oil filter. If it did, it would probably clogg up on about 1K-2K moles. The transmission does not deal with combustion by-products that create acid and sluge.
The transmission filter is more like a strainer than a filter. It only blocks the larger pieces of debris that get sucked up by the pump. Nearly all the matierial that gets blocked by the filter will fall to the bottom of the transmission pan when the engine is shut off and the transmission pump is no longer pumping fluid.
Once they fall down into the pan, any ferrous metal particals are trapped by the magnet in the pan. The other non-ferrous metals or clutch friction material will also fall harmlessly to the bottom of the pan, and since they are heavier the too fall to the bottom of the pan and do not create any problems. Any partical that is small enought to pass through the filter is too small to cause damage to the transmission.
The transmission is not threatend by the debris that sits in the bottom of the pan...That stuff is not circulating through the transmission. The real threat to the transmission is heat and the heat problems is very cyclic.
When your transmission fluid gets hot, it can be become burnt and damaged. If the transmission is burnt, it does not perform it's job as well, causing the transmission to slip slightly when shifting. This slipping of the friction clutches and bands generate even more heat, which further increases the damage to the transmission fluid.
Transmission fluid is used as much for it's hydraulic and cooling properties as it is a a lubricant. If the fluid is not changed regularly the fluid will turn to a gummy varnish-like substance that will coat the parts and harden and is what really distroys transmissions.
Transmission filters were always changed when the fluid was changed because you had to drop the pan to change the fluid (very few vehicles have ever had transmission drain plugs), so it made good sense to change the $7-$10 filter while you had easy access to it. In truth, the transmission filter only needs to be changed every 100K miles if the fluid is changed or flushed regularly.
Since the transmission relies heavily on the fluid that is not worn out, getting as much of the old burnt fluid out will do more good for your transmission than changing the filter. That means that a transmission flush removes about 97%-98% of the old fluid from the transmission, transmission coolers, and torque converter than a conventional fluid change where the pans is dropped and only about 50% of the fluid actually drains out.
Many auto manufacturers have gone to using 100% synthetic transmission fluids and only require tranmission service every 100K miles. That means no fluid changes, and no filter changes for 100K mmiles. Typically these tranmission don't even have a dipstick so you never have to check the fluid level. Of course if you see a transmission fluid leak, you need to get it into a shop to repair that leak.
You will probably hear a lot of disagreement about transmission flushes vs fluid/filter changes. Most of the old school mechanics will claim you MUST change the filter, buy that's not true today with modern synthetic and semi-synthetic fluids used on these late-model transmissions. I actually have some serious doubts that changing the transmission filter was ever as necessary on the older cars as much as it was one of those "Since you have to drop the pan to change the fluid, You might as well change the filter" items.
I know of a lot of people who drove vehicles for 200K miles with the body nearly rusted off and never once changed their transmission fluid. In fact the transmission was probably the only thing working right on the whole vehicle
