Old Transmission Filters

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THE DANGER OF CHANGING THE ATF

I'm no slushbox expert, but this is how I understand it:

A) Starting with a good trans & the right fluid, over time, debris is generated in the trans due to normal wear & contamination. The fluid contains detergent additives that keep this debris suspended in the fluid until it can flow back to the filter to be removed.

B) But the fluid only contains SO MUCH detergent. So if it's not changed on-schedule, the debris doesn't get suspended, and it settles out all over the trans. But this alone doesn't cause any immediate problems, which is why so many people neglect the trans fluid for so long.

C) Eventually, someone realizes how old the fluid is, and changes it with fresh detergent-rich fluid. This begins to break up the deposits, but it also loosens large chunks, which can block up the valve body's fine passages & ports, causing MAJOR damage.

D) From what I've seen, there are 2 possible ways to avoid this damage:
1) rebuild the trans
2) change the filter & fluid once, using decent aftermarket ATF. It's also a good time to add the drain plug kit. Then drive 50-200 miles to break up most of the deposits. Then change the fluid & filter again, using MotorCraft Mercon. If the trans goes out after that, it was going out anyway.

Owner caption March 2005 · Photo 962 of 5000