Mrrabbit seems to have gotten out on the wrong side of his hole this morning. But he's basically right. There are very limited (if any) options for alternate internals on these, or in fact any hubs.
Hubs are just about the most durable and long lived components on a bike. Give your hubs a thorough overhaul, and there's a good chance you won't need to spend a dime. Or replace those few parts that need it to keep them working like new.
There are many places to upgrade bikes, but short of replacing hubs entirely, this isn't one.
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