Air Disc Brakes
- Park the vehicle on a level surface, shut down the engine, and set the parking brake. Chock the tires. Once the tires are chocked, release the parking brake.
- Grip the caliper/carrier assembly by the chamber and verify that it slides in and out freely. Free play movement is 0.024 to 0.043 in (0.6 to 1.1 mm).
- Check the caliper mounting bolts by hand to see if they
are loose. Use a torque wrench set to the applicable torque value
and the Meritor extension tool 3256B1354 to check the caliper mounting
bolts. The Meritor extension tool will only work on M20 axial mounted
bolts; radial calipers use a unique hexhead bolt. See Table. and Table.. If the caliper mounting bolts turn at all, take the vehicle to
an authorized Western Star dealer for repair. If the bolts do not
turn, no further work is needed.
Table 1, Caliper Mounting Bolt Torque Values
Caliper Mounting Bolt Torque Values Caliper Description Torque: lbf·ft (N·m) Bendix, Axial Mounted
375±25 (508±34)
Bendix, Radial Mounted
225±22.5 (305±31)
Meritor, Axial Mounted
400±50 (542±68)
Meritor, Radial Mounted
Wabco Maxxus, Radial Mounted
295±22 (400±30)
Table 1, Caliper Mounting Bolt Torque Values
Table 2, Torque Compensation with Meritor Extension Tool 3256B1354
Torque Compensation with Meritor Extension Tool 3256B1354
All torque settings are ±40 lbf·ft (±54 N·m).
Compensation is calculated for a 43.5 inch (110.5 cm) nominal torque wrench using Meritor extension tool 3256B1354 at various angles.
Table 2, Torque Compensation with Meritor Extension Tool 3256B1354
Angle View
Extension Angle (degrees)
Wrench Length ~~*~inches (cm)]
Target Torque ~~*~lbf·ft (N·m)]
Tool Setting ~~*~lbf·ft (N·m)]
0
43.5 (110.5)
400 (542)
334 (453)
45
364 (494)
90
400 (542)
135
444 (602)
Table 2, Torque Compensation with Meritor Extension Tool 3256B1354
Important: The following step to inspect the caliper mounting bolts should only be performed at the initial maintenance (IM) interval.