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Piston Return Spring
1. Inspect the return spring for a free height
dimension of 22.15 mm (0.872 in.). A measured
height of less than 21.59 mm (0.850 in.) is an
indication that the brake assembly has been
subjected to high temperature operation, result-
ing in permanent set of the spring. This causes
loss of spring force at working height.
2. Measure the spring force at maximum service
deflection of a spring tester as shown in Figure
6-23. Use an outer spring guide for test setup
purposes.
FIGURE 6-23. INSPECTING PISTON RETURN
SPRINGS
1. Tester Arbor
2. Outer Spring Guide
3. Tester Table
Setup for inspecting piston return springs at
maximum operating deflection. Set up tester
as at (A), disregarding any force scale read-
ing; install return spring over outer spring
guide, compress slowly until dial indicator
again reads zero, read spring force on tester
force scale.
J06025 10/06
4. Return Spring
5. Tester Force Scale
Armature Speed Rear Disc Brakes
3. Set up the dial indicator between the tester
arbor and the table. Place the outer spring
guide under the tester arbor. Lower the arbor
firmly onto the spring guide. Disregard any
tester reading. Hold the arbor in this position
and set the indicator dial to ZERO, as shown in
View A. Figure 6-23.
4. Raise the arbor. Place the return spring over
the spring guide and lower the arbor slowly until
the dial indicator again reads ZERO. Read the
spring force on the tester scale, as shown in
View B, Figure 6-23.
This value is the spring return force exerted under
maximum deflection installed in the piston subas-
sembly. Because of the manufacturing tolerances,
this can be as low as 113 kg (250 lbs), but will usually
measure greater than 136 kg (300 lbs). It is recom-
mended that springs measuring a lower force than
113 kg (250 lbs) under these test conditions be
replaced.
J6-19
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