Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
Brake Master Cylinder: Fundamentals and Basics
Notes, Warnings, and Hints
REMOVAL
WARNING: DOT 3 or DOT 4 brake fluid is very corrosive to your vehicles finish.
Removing master cylinders can be a messy process. To prevent or minimize any possible damage perform the following:
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Siphon all brake fluid from the master-cylinder reservoir prior to removal.
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Use a fender cover to protect the vehicles finish.
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Use a drip pan to catch all fluid that leaks from the master-cylinder during removal.
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Any brake fluid which contacts the vehicles finish should be washed off immediately.
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Any brake fluid which drips onto electrical connections should be immediately removed (aerosol brake cleaner works well for this).
After the brake lines have been disconnected from the master-cylinder place vacuum caps over ends of the lines to prevent further leakage or
contamination.
Once the master-cylinder has been removed place it in a drip pan. Although the reservoir is empty, brake fluid trapped within the cylinder bore
will continue to slowly leak out.
OVERHAUL
WARNING: Never hone aluminum cylinders, if deposits cannot be removed with crocus cloth the cylinder should be replaced.
Check the cylinder bore for excessive clearance. With the piston installed you should not be able to install a 0.006 inch feeler gauge between
piston and cylinder. If the clearance is greater than 0.006 inches the cylinder should be replaced.
When installing the piston and seals into the cylinder always use clean brake fluid or assembly lubricant to lubricate the components.
INSTALLATION
Prior to installation the master-cylinder should be bench bled (this can be done on the vehicle but it is much easier on a workbench.
NOTE: Normal brake bleeding procedures will not remove air which is trapped in the cylinder bore area of a master-cylinder.
Attach the brake line fittings prior to snugging down the master-cylinder retaining bolts. The fittings are much easier to start turning when the
master-cylinder is still loose.
WARNING: Remember to tighten the retaining bolts after the brake lines are installed and tightened.
When snugging down the retaining bolts, alternately tighten them in small increments. This prevents the master-cylinder or push rod from
becoming cocked.
Upon installing the master-cylinder the entire brake system (front and rear) will need to be bled. Air enters the brake system as soon as the brake
lines are removed. It only requires a very small amount of air in the system to create a soft brake pedal.
WARNING: Never test drive a vehicle after a master-cylinder replacement until a firm brake pedal with a 75% reserve is established.
