With a dual chamber master cylinder, the rear line from the master cylinder (next to the push rod, larger reservoir) goes to the front wheel (usually discs), while the front line (farthest from push rod, smaller reservoir) goes to the rear wheels (usually drum). If one of' the lines or hoses breaks, you'll still have front or rear brakes to stop the car. Late model cars have gone one step further, using a four port master cylinder. Two ports from each chamber (one with a residual check valve for rear drums) helps split the brake system diagonally. One front brake and one rear brake are now fed by each chamber (check the photo). Now if you lose any wheel, you'll still have a front and rear wheel that will stop the car in a relatively straight line.

If your single chamber cylinder has an integrated brake light switch, you'll need to add a brake light switch T'ed into either front or rear lines out of the master cylinder. These switches are typically threaded into the casting. At the parts house, you can ask for ~ hydraulically actuated electronic stop light switch, Borg Warner number S-194. Installation can be accomplished with a three way T (Everco # 652-B) that has 1/8-inch pipe threads on top (for the switch) and threads for 3/16-inch brake lines on each end.

You'll also need to separate the front and rear lines where they are T'ed together under the chassis. This means you'll need to buy another length of 3/16-inch brake line with ends, to go from the T to the master cylinder. If you don't have a double flaring tool to attach the correct ends on the new brake lines. since there are now two different sizes on the dual chamber master, you'll need to adapt. At the master cylinder outlets, you will notice you'll need an adapter in the 1/2-20 front wheel port (nearest the push rod hole). Everco number 7817 adapts from 1/2-2() to 3/8-24 for 3/16-inch brake line, while Everco number 7818 adapts 7/16-24 to 3/8-24 for the rear wheel brake line port fitting on the master (farthest from the push rod hole). All aftermarket 3/16-inch diameter brake line has 3/8-24 fittings on the ends.

Raybestos # MC 39037 (R.H.) (cast iron) 7/8 bore
    '78-81 Ford Fairmont  •  Granada  •  Futura  •  Zepher (Mercury)

Raybestos # MC 39531 (R.H.) (aluminum) 21mm bore
    '81-86 Ford T Bird  •  '82-86 Mustang  •  '83-86 Marquis (Mercury)

Raybestos # MC 39310 (R.H.) (cast iron) 7/8 bore
    '81-83 Ford Escort  •  Explorer  •  Lynx  •  Mark 7 (Lincoln)

Raybestos # MC 39027 (L.H.) (cast iron) 7/8 bore (L.H.)
    '76-80 GM Monza  •  Sky Hawk  •  Starfire  •  Sunbird

You may be asking yourself what will happen if I go from a one-inch diameter bore to a 7/8-inch bore? This will up the line pressure. but lengthen the pedal travel. The pedal will be firmer when the line pressure reaches the point where the brakes are being applied You won't have to apply as much pressure to stop the car You will also have the option of right or left exit ports from the master cylinder, depending on your pedal arrangement (swinging pedals or under-floor pedals). The reference point for right or left exit lines is with the push rod port facing the viewer.

Before '68, the residual pressure valve was in the master cylinder bore. After '68, RPVs were typically placed at the exit ports, just behind the inverted flare. where they arc easily removed with a sheet metal screw. In fact some are threaded— some kits include a screw if you are using the master on a disc/disc system (remove both). The internal components in the masters listed are the same and can be used for both applications by simply removing the residual check valve for the disc end of your car, or remove both valves for disc/disc applications, and leave the check valves if you have four wheel drum brakes (check photos).