Aisin Warner AW55-50/51SN and AW50-42LE
As we all know, automatic transmissions are extremely complex and expensive technical units, which are expensive to repair if they no longer fulfill their function.
Therefore, a vehicle manufacturer should be careful to keep abrasion, such as occurs in the 'normal' operation of a transmission, from the same. An external oil filter can do this job very well.
At this point I would like to thank my vehicle manufacturer that I and other people were charged with unnecessary costs, just because some people thought with a sharp pencil, an oil filter in an automatic transmission is completely pointless!
For me there is absolutely no excuse for this, I call this the willful destruction of someone else's property.
I now own the third Volvo with automatic gearbox, of course, all gearboxes had problems with the abrasion of the clutches, which got stuck in the solenoids and in the valvebody and led to more and more problems with increasing running time.
In my 850s (GLT, TDI), the torque converter lock-up caused massive problems by sliding under load, and the gears did not switch properly. With my V70 P26 MY 2002 I had the 3rd gear problem for which Volvo has a update kit (Volvo OEM 30751262 Auto Transmission B4 Servo Update Kit). In addition, this gearbox shifted more rough than smooth and also has problems with a slightly slipping lock-up at low speed.
All 3 gearboxes now run clean again, the TDI gearbox now has 550,000km, the GLT gearbox 78,000km and that of my V70 has 320,000km.
I installed an external oil filter for all gearboxes, as can be bought in the accessories trade. The filter is a standard oil filter as used for engine oil. After installing the filter, it takes approx. 5,000km until the gearbox starts to normalize. This is how long it takes for all the dirt to be washed out of the gearbox.
Flushing the gearbox has not led to the desired success in all three gearboxes, since flushing only rinses a fraction of the dirt. An external oil filter fishes even the last remnants from the oil after a certain time, which could even lead to the fact that the 'lifetime' filling becomes a reality. Then the oil could actually last a gearbox life. Just change the filter every 30,000 Km and fill the filter with fresh oil again before installing it. This is not supposed to be a recommendation now, it's just my personal opinion.
The external filter even almost completely solved the 3rd gear problem with my V70, the gearbox only had the filter before the repair kit was installed, and the problem became less and less with every kilometer. This indicates that the solenoids shift better when the dirt is filtered out of the oil.
Also, I don't think Volvo's expensive oil needs to be used, especially not for rinsing. I use Ravenol ATF Synthetic T-IV Fluid, which is explicitly recommended for these gearbox types.
So folks, just build your own external oil filter into the system. To do this, simply disconnect the return line to the gearbox on the oil cooler and grind in the oil filter there - done. With filter holder, filter, lines and connection material costs about 100 euros. This is much cheaper than a broken gearbox.