Join Date: Sep 2008
Location: Sesame Street
Bikes: Swobo Folsom, Diamond Back Master TG, Mongoose Alta, Huffy Daisy Tandem
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"Sealed Bearings" can refer to one of two things:
1. The bearings are regular loose balls between a pressed-in cup in the hub and a cone on the axle, or
2. The bearings are cartridges, that is, they are a sealed unit that includes the bearings, an inner race (that is pressed into the hub), an outer race (that rides on the axle), and a rubber or metal seal on each side of the cartridge. These variety of bearings are replaces as a unit and generally aren't worth repacking with grease.
With that said, you will have to check the hubs by removing the locknut, any spacers, and the cone from axle in order to determine which type of "sealed bearings" they are.
As far as I know, Shimano has never utilized cartridge bearings in any of its stock hubs, so you can be fairly sure that they are not the latter type of "sealed bearing". However, it is certainly worth a look. As for the front hub, you will definitely need to pull off the axle hardware to be sure, as it could be either type. Good luck!