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Vacuum Pump Oil Leak


RaDi90Hybrid

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At the end of the day this Wabco vacuum pump design is seriously flawed.

It is a constant pump, that is, it will continue to create a vacuum even when it is not required, as in when you are driving on a motorway and not using your brake, consequently there will be a high vacuum in the end of the cylinder, this vacuum will draw oil past the piston and into the "cylinder head".

This oil is then compressed and consequently forced out of the cylinder head rubber seal and out of the discharge poppet valve welch plug.

Part of the design problem is the material the piston is fabricated from, being a nylon type material it is very difficult to machine it to any precision limits, consequently it is a poor fit, the other is that there is no oil sealing ring on the piston.

Were the design to be rectified firstly the piston would be precision machined from a suitable alloy and fitted with an oil ring to prevent oil passing the piston and into the cylinder head. Secondly the return spring would be modified so that it was equal to the required vacuum in the servo unit, if this was the case once the servo vacuum had been achieved then the piston would be held by the vacuum at the "TDC" position and the piston plunger held off off the cam and would only return if the vacuum was lost - with brake actuation or due to small leakages.

The cheaper long term solution is to replace it with an electric diaphragm type pump and wired to the ignition circuit.

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