Rebuilding The Caliper - GMC G Service Manual

PARALLELISM
Parallelism of a brake rotor refers to the inner and outer
surfaces of the rotor being parallel. To determine rotor par­
allelism, measure the thickness of the rotor at four or more
points around its circumference. Each measurement must
be made at the same distance from the edge of the rotor.
The rotor thickness must not vary more than 0.013 mm
(0.0005-inch) from point to point.
MACHINING
Since accurate control of rotor tolerances is necessary
for proper performance of the disc brakes, machining of the
rotor should be done only with precision equipment.
All brake rotors have a minimum thickness dimension
cast into them. This dimension is the minimum wear dimen­
sion and not a refinish dimension. Do not use a brake rotor
that will not meet the specification after refinishing. Replace
it with a new brake rotor. Refer to "Specifications" in this
section for final machining tolerances.

REBUILDING THE CALIPER

3000/3100 MODEL CALIPERS
M Remove or Disconnect (Figure 16)
• Drain all the fluid from the caliper.
• Pad the interior of the caliper with clean shop towels.
CAUTION: Do not place your fingers in front of
the piston in an attempt to catch or protect it
when applying compressed air. This could
result in serious injury.
HYDRAULIC FOUNDATION BRAKES 5A2-7
NOTICE: Use just enough air to ease the piston
out of the bore. If the piston is blown out— even
with padding provided, it may be damaged.
1. Piston (22) by directing compressed air into the cali­
per fluid inlet (figure 17).
• Use just enough air pressure to ease the piston
2. Boot (23) (figure 18).
• Use care not to scratch the caliper's piston
3. Piston seal (21).
• Do not use any type of metal tool.
4. Bleeder valve (20).
Clean
• Bleeder valve, caliper bore, caliper passages and pis­
ton with denatured alcohol. Use dry, filtered com­
pressed air to dry parts and blow out passages.
M Inspect
• Piston for scoring, corrosion and any damage to the
chrome plating. Replace if any of these conditions are
found.
• Caliper bore for scoring, pitting or corrosion. Use
crocus cloth to polish out any light corrosion. Replace
caliper if corrosion cannot be removed.
out of the bore.
bore.