A thin layer of fine gray paste on the transmission pan magnet is normal: it is iron dust from gears and other steel parts wearing in over thousands of miles. Visible flakes, slivers or chunks of metal, a thick coating that hides the magnet, or lots of brass, aluminum or friction material in the pan are signs of internal wear. The pan magnet only catches steel and iron, so look at the bottom of the pan and the filter as well.
What the pan magnet does
Automatic transmissions have one or more magnets in the pan to catch ferrous particles before they reach the filter, the valve body and the pump. Cleaning the magnet at every pan service and noting what is on it is one of the simplest health checks you can do.
Reading the debris
| What you see | What it usually means |
|---|---|
| Thin gray paste on the magnet | Normal wear |
| Thick fuzz covering the magnet | Heavy wear or a long service interval; watch closely |
| Steel flakes, slivers or chunks | Gear, bearing, drum or thrust washer damage |
| Brass or bronze glitter in the pan | Worn bushings or thrust washers |
| Aluminum particles | Wear in the pump, case, drums or valve body |
| Dark fibrous material | Clutch or band friction material wearing away |
Brass, aluminum and friction material are not magnetic, so they settle on the pan floor and in the filter rather than on the magnet.
Check the fluid too
Burnt-smelling, dark fluid with debris confirms internal wear; see transmission fluid color. Fluid that looks and smells normal with only fine paste on the magnet is a good sign.
What to do next
- Normal paste. Clean the magnet, fit a new filter and gasket, refill with the correct fluid; see how to change a transmission filter.
- More than normal. Photograph it, service the transmission and check again sooner.
- Chunks or lots of non-ferrous debris. The transmission has internal damage. Changing the fluid will not repair it; plan a rebuild or replacement.
Should you flush a transmission with debris?
A machine flush does not remove the cause of the debris and can move particles around. If the pan shows real damage, diagnose the transmission first; see transmission flush vs change and signs of a bad transmission.
When the transmission needs replacing
If the debris says the transmission is failing, compare options in rebuilt vs used transmissions and browse units by code on transmissions. Replace or thoroughly flush the cooler and lines when installing a replacement, so old debris does not reach the new unit. If the pan gasket leaks while you are in there, see transmission pan gasket leaks.
More guides: transmission line pressure.
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