TA05 not very smooth

I started to realize my TA05 is not very smooth.  

On motor (27T), full chicken, release, then the wheels will stop right away, not much free spin.

Take out the motor, push the car on the table.... still not very smooth

Played for a while, need to clean up?  What usually causes it?  Or that's TA05's problem?

可能bearing出左問題, 是但一粒死左吾識轉都會係噤(我指拆左摩打用手推 )

你係唔係用頭單先?唔係的話應該係唔會有好耐自己空轉喎......如果會自己空轉咁樣反而大問題喎.......不過間唔中打散架車出嚟洗下啤鈴都好應該O既動作嚟~