Gotrax APEX User Manual page 16

If you notice that the tiller is loose or wiggles while
Tightening the Tiller:
If the disc brake is too tight, use the 4MM
Adjusting the Disc Brake:
to extend the brake wire and retighten the screws. If the disc brake is too
loose, loosen the screws and pull the brake wire to extend the brake wire
and retighten the screws.