The dual master cylinder has a safety feature which the single unit lacksif a leak develops in one brake circuit (rear wheels, for example), the other circuit will still operate.
Failure of one system is immediately obviousthe pedal travel increases appreciably and a warning light is activated. When the fluid falls below a certain level, a switch activates the circuit.
REMOVAL & INSTALLATION
See Figures 1 through 6
- To remove the master cylinder, use a tool such as a turkey baster to remove the brake fluid from the reservoir.
- Disconnect the switch connectors using a small screwdriver. Disconnect the brake lines at the master cylinder. Plug the ends with bleed screw caps or the equivalent.
- Unbolt the master cylinder from the power brake unit and remove. Be careful you do not lose the O-ring in the flange groove of the master cylinder.
- Installation is the reverse of removal. Be sure to replace the O-ring between the master cylinder and the power brake unit, since this must be absolutely tight. Torque the nuts to 12-15 ft. lbs. Be sure that both chambers are completely filled with brake fluid and bleed the brakes.
See Figures 7 and 8
- To disassemble pull the reservoir out of the top of the cylinder.
- Remove the screw cap, strainer, and splash shield.
- Unscrew the cover caps and take out the inserts and O-rings.
- Push the piston inward slightly and remove the stop screws.
- Remove the piston stop-ring in the same manner, then pull out the piston and other components.
- The spring must be unscrewed from the piston.
- Clean all parts in clean brake fluid.
- Check the housing bore for score marks and rust. Do not hone the cylinder bore. If slight rust marks do not come out with crocus cloth, replace the housing.
- Assembly is the reverse of disassembly. Before installing the pistons, coat the sleeves of both pistons with brake fluid.
Do not force the pistons into the housings. A special tool is available to install the pistons, but if it is not available, install the pistons very carefully with a slight twisting motion. The special assembly tools can be fabricated in the shop from light metal alloy, according to the dimensions given.
See Figures 9 and 10
Always bleed the brakes after performing any service, or if the pedal seems spongy (soft). The location of the bleed screws can be seen by consulting the illustrations throughout this section. Prior to bleeding each wheel, connect a hose to the bleed screw and insert the hose into a jar of clean brake fluid.
On dual master cylinders, bleed only the circuit that has been opened. If both circuits have been opened, first bleed the circuit connected to the pushrod bore starting with the wheel farthest from the master cylinder, then bleed the other circuit.
- First have an assistant pump the brakes and hold the pedal.
- Then, starting at the point farthest from the master cylinder, slightly open the bleed screw.
- When the pedal hits the floor, close the bleed screw before allowing the pedal to return (to prevent air from being sucked into the system).
- Continue this procedure until no more air bubbles exit from the bleed screw hole, then go to the next wheel. Fluid, which has been bled from the system, is filled with microscopic air bubbles after the bleeding process is completed, therefore it should be discarded.