Some people rebuild a lot of transmissions and don't like the idea of replacing the converter every single time; without having an actual reason stemming from a thought process. External inspection can easily condemn a converter, but to go beyond that requires the aforementioned process. If you have misplaced your thinking cap, then by all means slap a new on in there every time. For those who dare to use the brains God gave them, the following steps should be enough to make you a converter expert. Use a pair of snap ring pliers and reach down inside the converter to grab the stator and pull up and down on it to check end play. More than .050 is suspect. When you check the clutches for wear, you can determine how much trash or greasy dust should be in the pan. If your clutches aren't very worn; that is, the trans still operated fine, then is would be doubtful that the converter is contaminated; as long as your filter isn't blown, and you are running an actual filter; not a screen. If the fluid is black; replace it. Also check the converter where it rides in the pump bushing; any wear at all; trash it. Same goes for the front seal causing a wear groove on the converter; any wear; trash it. Lastly, especially on a 904 converter; check it in four places for cracks; at the bottom corners of the slots. Wipe it off; tap it with a hammer and any crack will show a line of oil displaced by the tap. Unsure? Wipe it off again and tap it again; it will repeat. Cracks hold a lot of oil. They crack because the metal is thinner a short distance down inside the converter. Just stick your finger down inside and you'll feel a step down where the metal gets thinner; maybe 1/4" from the bottom of the slot. If any metallic particles come out of the converter; trash it. If your pump is worn into the stator support (where the center gear rides) trash it. If the two prongs are broken off the inside of the center pump gear; trash it. That being said; I replace 1/3 of all 904 converters. If you ask a transmission shop to check your converter; they will just look at you like you're living in a dream world. Everybody who sells converters will tell you to replace it or you're an idiot. 76,000 miles is nothing for a converter that has always maintained proper fluid levels. On the other hand, I think O'Reilley's sells rebuilt converters for under a hundred bucks. I'm just words on a screen...but if you have any questions feel free to ask. I don't think I left anything out, but I'm still anticipating the day that I'm wrong.
