http://www.one-ten-rcforums.com/4wdr...ic.php?id=1540
Sorry no internal pics to hand of hold down roller. Mine is as simple as an M3 bolt(I think) with a motor bearing (same ID as screw). I then drilled a deliberatly oversize hole in the chassis and used a big washer (blue anodized one in pic) so you could position the bolt in the right place (paper width) off the belt so it only touches when the belt tries to skip.
Does the belt only skip on the drive pulley - yes I'm 99% sure.