Where is the iron sludge in the rear axle coming from?

Greenie

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It's a 4.11 limited slip full floating axle with 280K miles. I'm finding iron sludge attaching itself to the magnet in the fill plug and on the speed sensor at the top of the differential. This eventually causes the transmission to go into the limp mode until I clean the sensor (shutting off the engine and restarting clears the limp mode which returns eventually) . It's been happening for years and the rear axle is fine otherwise - although I think the limited slip qualities have degraded from what it was new.
Where is this ferrous material coming from?
Differential work in Bangor Maine is very limited - I'd like to keep this truck.
 

u2slow

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The friction plates in the trac-lok do shed material. Then there's bearing metal. It's probably time to renew things at 280k miles.

You could try adding another magnet to help contain the metal particles better.
 

Ranchdweller

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If you have enough metal to cause the problems you are talking about, you need to disassemble and find the worn parts. Could be gear or bearing. Might be making some noise.
 
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