Rebuild service for Hydro Unit aka Hydraulic Pump

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You send in your malfunctioning E46-Series hydro unit, and Top Hydraulics rebuilds it. The rebuild includes electric motor replacement or rewinding if necessary, service and check of all internal pump components, upgrade of internal seals in the pump, and full bench test to assure that factory specs are exceeded. Three years warranty.

p/n 8 234 530 or 54347025595 or HB70346-002



The most common failure symptom on used BMW E46 hydro units is a gradual loss of pressure and power. There are various possible reasons for gradual power loss inside the pump/hydro units, ranging from degrading electric motors through pump pistons wearing out and check valves bypassing, to pressure regulators failing. Top Hydraulics will check that all these components meet or exceed factory specs and exchange or upgrade them if necessary. Bench testing includes all valve functions, pressure test, flow test, extended load test, and test for leaks, to make sure that factory specs are exceeded before the pump ships back. Beware when purchasing used pumps that those may actually be units that are still pumping, but are not able to complete the convertible top's opening or closing cycle without manual assistance.

Some of these pumps have external leaks (you may find the foam casing soaked in hydraulic fluid). The most common source for external leaks on these pumps are the port seals. Port seals are tiny seals of special shape that are sealing the hydraulic lines when they are plugged into the pump. The port seals are behind brass bushings. These bushings are pressed into the pump housing, and they are made to 1/100 mm precision. Any DIY repair attempt would destroy the bushings. Top Hydraulics replaces the original port seals with an improved version made of Viton, which has practically unlimited shelf life. Before assuming that the pump is leaking externally, check the hydraulic lines going into the pump to make sure they are dry.


The fill plug is a metric Allen bolt. It is the one closest to the level marker on the reservoir. Make sure to have a fitting Allen wrench, so that you do not strip the inside hex of the plug. Please drain the fluid through the drain plug before shipping the pump to us.

You can save some money by using Mercedes fluid 0009899103 or FeBi 02615 - they are fully compatible with your BMW 3-Series cabriolet hydraulics.


Turn around once we have your pump and payment is 1-3 days. Additional cost applies if the reservoir arrives broken or the aluminum ring around the motor has been crushed beyond repair. Please wrap the pump in absorbent material and put plastic bags around it, buffer your parcel well inside, ideally double-box, and tape up well. Take special care to protect the thin aluminum wall at the end of the reservoir from getting crushed in transit - it seals the end of the reservoir. Top Hydraulics ships back inside a USPS Priority Mail Large Flat Rate Box - $15 inside the USA.

International customers: please select the $55 FedEx International shipping option during checkout - the option will appear after you have entered and saved your shipping address.

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