Dorman 904-810 Gear Driven Mechanical Vacuum Pump
Updated June 19, 2026
The Dorman 904-810 is a gear-driven mechanical vacuum pump designed for 1994-2002 Dodge Ram 2500 and 3500 trucks. It provides the vacuum needed for HVAC controls, brake boosters, and 4WD systems on both diesel and gasoline engines. This pump is a direct replacement for the original equipment unit and is manufactured as a new part, not remanufactured, with an improved bearing design to address common failure points.
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Function and Design
This pump is gear-driven directly from the engine's camshaft or timing gear, meaning it operates mechanically without electrical power. It uses a rotating vane or piston mechanism to create vacuum. The Dorman unit features barbed connectors and multiple inlet/outlet sizes (3/8", 1/2", 5/8", 3/4", 1") to accommodate various hose configurations. Dorman re-engineered the original needle bearing on the cam, which was a common failure point, to improve durability.
Vehicle Compatibility
The 904-810 fits 1994-2002 Dodge Ram 2500 and 3500 trucks equipped with the 5.9L Cummins diesel (L6 359), 5.2L V8 (318), 5.9L V8 (360), and 8.0L V10 (488) engines. It is also compatible with some 1994-1996 Dodge Ram 2500 models with the 5.2L and 5.9L V8s. Always verify fitment with your vehicle's year, make, model, and engine.
Common Failure Symptoms and Diagnosis
A failing vacuum pump often produces a whining or grinding noise from the engine bay due to bearing wear. Symptoms include loss of HVAC vent control, weak or no brake boost (hard pedal), and inability to engage 4WD. A simple test is to disconnect the vacuum line and check for suction at idle; low or no vacuum indicates pump failure. Dorman's improved bearing design aims to prevent the premature failure common in original pumps.
Installation Notes
The pump is gear-driven, so installation requires aligning the drive gear with the engine's gear train. It typically mounts to the engine block or timing cover. A new gasket is included to ensure a proper seal. Ensure the barbed fittings are securely connected to the vacuum hoses. Torque specifications should be followed per the vehicle's service manual. The pump is a direct bolt-on replacement.
