I wanted to pull the GT BB apart, but I'm afraid I'd never get it back together.
from bikepro -
The sealed bearing cartridges marked #61903RS are machine pressed onto the spindle, which is generally a good thing, but there is a complication. After one of the bearing cartridges is pressed on, an anodized aluminum tube with the "GT" logo is placed over the spindle before the second cartridge is pressed in place. This tube is precise fit and conforms perfectly to the outer diameter of the cartridges.
Most other B/B with machined pressed bearings have a gap between the water sleeve and the bearing that enables you to slide a piece of plate steel to support the bearing as you rap with a hammer to free a failed bearing for replacement. These pieces fit so tightly, and have no gap, replacing a bearing should it fail is likely to leave some real physical damage on the remaining parts.