Being new to auto transmisions and Ford Rangers I read up on the threads for changing the fluid.

At 125,000 miles I didn't know it's history. It had started to clunk when cold going from 1st to 2nd. A friend suggested to start by changing fluid and filter.

I'd read about the dangers of flushing and oil change shop methods.

In the end I decided to do it myself taking the pan off.

The pan had a thick layer of sediment to it. No metal fragments. There was a strip magnet stuck to the bottom of the pan covered by the sediment but no fragments.

Before doing the change I had sucked out at least 1/2 a quart trying to lower an overfilled transmision. Today I took out well over a gallon. The fluid was dark brown.

Cleaned the pan, put new filter in and added 4 quarts. Went for a test drive and it's a different transmision. I had no idea a fluid change to the correct level would make such a difference.

How or where is all that sediment from? Is it a bad indicator to the transmision's condition?

Thanks
Al