Ask the Editors: Mysterious Black Goo

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Oil where there shouldn’t be.

Dear ATVC: I’m replacing the brakes on my 2004 Honda TRX250EX and found (what I think) is gear oil on the brake drum.  Why is this?


Considering your machine is equipped with a manually-activated, sealed rear drum system, we can immediately rule out common culprits like a leaking cylinder spilling hydraulic brake fluid into the assembly.

Additionally, while unlikely, since the axle traverses the drum housing, it is possible that axle grease was present within the system and over time flung up onto the drum itself.

The most likely culprit, however, is that water made its way inside the drum assembly, gathered up grease and grime and put a nice coating all over everything.  How can we be sure?  Honda is aware that this happens and thought to include a drain plug on the outer housing so that you can let this goop out yourself regularly after particularly wet or muddy rides.

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