Hi, I have a 2011 Subaru Tribeca with 100k miles. Long story short, I went to a transmission shop for a transmission fluid change and they did a transmission flush that caused a very annoying shudder during the lockup of the transmission, but unfortunately I took too long to realise the problem.

After this incident, doing some research, I found out that, like Hondas, Subarus are very sensitives to what ATF you put in the transmission. The first thing I've noticed, according to the bill, was that the transmission shop used Valvoline multivehicle ATF, but the owner's manual recommends Subaru ATF HP. The second thing was, before I start the car in the morning, the car was cold, the dipstick level was way above the full hot mark. In other words, the transmission shop used the wrong type of fluid and overfilled my transmission.

I decided to fix it myself. I went to a Subaru dealership and I bought 12 quarts of Subaru ATF HP. I did 4 cycles of drain and fill of the transmission, twice a week. Every cycle I drained out 4 quarts of the transmission, but I filled it with 3 quarts. After the 3rd cycle, the shudder was almost gone, but with the 4th cycle the shudder was completely gone and the dipstick level, after driving a while, was correctly on the full hot mark.

The transmission shop added 4 extra quarts of ATF in my transmission, I have no idea how my transmission managed to survive without apparent issues nor leaks. I should have done it myself in the first place. Leçon learned.