The Hydro-Boost® uses this pressure that is always circulating through it, to convert to pressure to apply against the master cylinder. The output of the Hydro-Boost is affected by three factors.We recommend pedal ratio be between 5:1 to 6:1. The pressure output from the pump. The master cylinder bore diameter. It is imperative that the system be clean. Any residual metallic sediment laying in an old pump or steering box, will be floated up and through the system when the fluid comes through on start up. If any of this sediment lodges in the relief valve of the pump, there will be no pressure from the pump. This will result in hard steering and no power brakes. These are re-manufactured Bosch Hydro-Boost units. These are not imported units commonly found. Product fits: 1958 59 60 61 62 63 64 65 Chevy Impala Belair Biscayne Caprice. This item is in the category "eBay Motors\Parts & Accessories\Car & Truck Parts & Accessories\Brakes & Brake Parts\Master Cylinders". The seller is "performanceonline-pol" and is located in this country: US. This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech Republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Greece, Portugal, Cyprus, Slovenia, Japan, China, Sweden, South Korea, Indonesia, Taiwan, South Africa, Thailand, Belgium, France, Hong Kong, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Bahamas, Mexico, New Zealand, Singapore, Switzerland, Norway, Saudi Arabia, United Arab Emirates, Qatar, Kuwait, Bahrain, Republic of Croatia, Malaysia, Brazil, Chile, Colombia, Costa Rica, Panama, Trinidad and Tobago, Guatemala, Honduras, Jamaica, Barbados, Bangladesh, Bermuda, Brunei Darussalam, Bolivia, Ecuador, Egypt, French Guiana, Guernsey, Gibraltar, Guadeloupe, Iceland, Jersey, Jordan, Cambodia, Cayman Islands, Liechtenstein, Sri Lanka, Luxembourg, Monaco, Macau, Martinique, Maldives, Nicaragua, Oman, Peru, Pakistan, Paraguay, Reunion, Vietnam, Israel.