well got it solved...
it was not the brushs!
-This picture they are halfway... ok, more 2 months to play
-This was the real problem.... the pinion is loose. Thank god it's that! I Get rid of the ten tooth, and puted a 11 tooth pinion. Works like new.
(the hole on the pinion is now biger then the engine arm, so it spins but the car wont move....)
i guess that puting the new tires, helped the pinion "habitueted" to bold ones, getting loose!!