This paper describes the Fuller truck retarder and some of its development problems. The equipment is designed as a braking device for large on-highway trucks operating in mountainous terrains with steep descent grades. Since such braking accounts for most of brake lining wear, the retarder will considerably reduce cost of relining and downtime. Up to 5% grades the retarder effects 100% of the braking; on steeper grades it contributes the major portion. Since new highway restrictions limit grades to 5%, it may be expected that the retarder will drastically cut costs in this area.