Abstract: A device comprising two oil reservoir tanks communicating with the two respective oil-hydraulic chambers of a tandem type master cylinder and also with each other through an upper and a lower interconnecting oil passage. One of the two tanks has a top opening for oil filling use and normally closed with a vented cap while the other tank is closed at the top and provided therein with an oil level detector means which comprises a stationary reed switch connected with an appropriate external alarm circuit and a permanent magnet vertically movable with the oil level in the tank to close the reed switch as the volume of oil stored is reduced to a predetermined minimum. With the device, even if one of the two oil-hydraulic lines connected with the master cylinder fails to function due to oil leakage, the other line can properly function without any pressure failure as, in the associated tank, a predetermined minimum volume of oil remains on account of the height of the lower oil passage.

Abstract: In a brake system including two independent hydraulic lines extending from a dual type brake master cylinder and connected to the respective rear wheel brakes, a novel pressure control device provided for automatically adjusting the ratio of the front to the rear wheel brake pressure for maximized overall braking efficiency and including failure alarm for warning the driver of any trouble in operation of the device or of any fluid leakage on the hydraulic lines without delay. The device includes a cylinder bore fitted with a pair of annular pistons and a balance piston extending axially therethrough. A pair of sealing rings are mounted on the balance piston at the opposite ends thereof to define each an input and an output hydraulic chamber, respectively connected with the upstream and downstream portions of the associated one of the two hydraulic lines and adapted to be placed in communication with each other with displacement of the balance piston from its neutral position.