I wanted to know how to open(replace) the ball bearing Retainer in order to change the ball bearing of the makita drill 6301LR

SOURCE: makita 18volt 6347 cordless drill

then you need transmision assy. item 14 in breakdown
see toolpartsdirect.com for further info on your drill

SOURCE: makita 650watt corded drill

tap the 3 jaw with hammer not too hard. then the sleeve clockwise

SOURCE: I need a bearing or all rotor for my makita hammer driver drill

They dont list just a bearing for the armature. They sell as an assembly. The part number for it is 629831-4. if you want to look at a breakdown of this tool go to Makitatools.com and type in your model number and click on parts breakdown.

SOURCE: i took apart my makita 8271d 14.4v battery drill

Check and make sure you put the clutch pack in right and not backwards. That is what it sounds like happened.

SOURCE: how to dismantle a makita

Check out the split drawing on this page.
If your makita does not have any outside accessible brush caps, you need to dismantle it.
lay it on the side, where the side with the screws securing the to halves together is facing up.
Remove all screws (some may be hidden under labels etc.) Gently pry the halves apart, locate the brushes disconnect their leads if any, and remove. Install new brushes and make sure the move freely, and that they are springloaded when in place. Gently rotate the rotor to ensure everything is ok . Reassemble and test drill. If the brushes leaves long streaks of noticeably large sparks, something has gone wrong or the rotor was damaged in the first place, causing excessive wear.