Ive seen them at the gear box end of the trannys as well as at the rear differential around here (we have ALOW of 4x4 trucks that use these as well as 'the good ol' boys in muscle cars) Some slow the tranny down (keep the rear brake system and leave it in gear to slow it) or at the rear differential (which will slow down the rear axle) That site doesnt seem to explain their system...But looks to be at hte gear box end. May be something different than what Im thinking. I dont know? e-mail their tech dept and see what they can give you on benefits.