Mitsubishi 1989-1993 GALANT Service Manual page 1234

SERVICE BRAKES -
Have the lip facing upwards.
TSB Revision
Rear Brake Wheel Cylinder
SERVICE POINTS OF DISASSEMBLY
When disassembling the wheel cylinders, disassemble both
sides (left and right) as a set.
4. REMOVAL OF PISTON CUPS
Remove the piston cup, being careful not to damage the
piston.
INSPECTION
Check the piston and wheel cylinder walls for rust or damage,
and if there is any abnormality, replace the entire wheel
cylinder assembly.
SERVICE POINTS OF REASSEMBLY
4. REASSEMBLY OF PISTON CUPS/3. PISTONS
(1) Use alcohol or the specified brake fluid to clean the
wheel cylinder and the piston.
(2) Apply the specified brake fluid to the piston cups and
the special tool.
Specified brake fluid: Conforming to DOT3 or DOT4
(3) Set the piston cup on the special tool with the lip of
the cup facing up, fit the cup onto the special tool, and
then slide it down the outside of the tool into the
piston groove.
Caution
In order to keep the piston cup from becoming
twisted or slanted, slide the piston cup down the
tool slowly and carefully, without stopping.