RD688S, Heavy Duty Trucks - Dump Trucks, Mack E7, 8 Spd, I have a 1998 Mack RD688S Tandem Axle Dump Truck for sale. It has a Mack E7 350 horsepower engine with 1,081,985 miles on it. The transmission is an Eaton Fuller 8 speed. The front axle is rated at 18,000 pounds and the tandem rears are rated at 44,000 pounds with a 4.42 Gear Ratio. The truck rests on a Mack Camelback 10 leaf suspension. The bed is steel. Call Ryan with questions., 350 Horse Power, Camelback Suspension, All Steel Wheels, Wheel Base, , Tandem Axle, Ratio,