After making repairs on or replacing the master cylinder of your 1985 GMC S-15, you will need to bleed the hydraulic system. This means getting the air out of the system. This can be a time consuming process unless you fill the master cylinder with fluid and "bench bleed" it before you reinstall the repaired master cylinder or install a new one. Bench bleeding gets the air out of the hydraulic system before reinstallation so the air does not have to push all the way through the lines. As a result the task is accomplished much more quickly.
Tools Used: Threaded plugs, Vise, Brake fluid, Wrench
Bench Bleed Clutch Master Cylinder
Insert threaded plugs into the cylinder outlet holes. This will keep the brake fluid from leaking out during the bleeding process.
Place the master cylinder in a vise to keep the cylinder in an upright position so that brake fluid cannot spill out of the reservoir during the bleeding process. Fill the reservoirs with brake fluid.
Loosen one plug at a time either by hand or with a small wrench, depending upon how tight they fit. Push the piston assembly into the bore to force air from the master cylinder. Tighten the plug and then return the piston to its original position. This will keep air from being sucked back into the master cylinder.
Repeat the stroking motion of the cylinder three or four times. Stop when no more air is being expelled from the system. Refill the cylinders on the master cylinder.
Move to the second plug. Repeat the process.
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