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U.S. 888-725-9355
Canada 800-387-3889
WHAT MAKES A GOOD BRAKE DRUM (continued)
5. SUMMARY: THE BEST BRAKE DRUM FOR OVERALL PERFORMANCE
Is a relatively heavy brake drum
Is made from temperature and wear resistant high tensile iron
Is precisely machined
Is balanced by machining rather than adding weights
MAXIMUM BRAKE FACE DIAMETERS
Maximum brake face diameters are indicated on Meritor Brake drums, i.e., the word “Max. Dia. 15.120 inches 384.05mm” will be found
on brake drums with a 15 inch, 381mm nominal brake face diameter. This means that for safe operation the brake face diameter should
never exceed 15.120 inches, 384.05mm from machining or wear.
Because we have no way of knowing the number of heat cycles or the severity of the cycles to which the drum has been subjected in
actual usage, we do not recommend reboring the brake face diameter. The user is best able to judge whether the drum has sufficient life
remaining to justify reboring. The maximum diameters are shown in the chart.
Meritor has engineered their brake drums to provide safe operation at the maximum brake face diameters, however, Meritor does not
machine these drums to maximum diameters and cannot control the methods that others use to re-machine them after they are put into
use.
Do not confuse maximum brake face with maximum rebore diameters. When the drum reaches the maximum brake face diameter, it must
be removed from service. There may be some instances where it is a good economic decision to rebore a brake drum but after rebore,
there must be some wear life left (at least .040 inches) prior to reaching discard diameter. Meritor does not recommend reboring brake
drums for the following reasons:
1. It usually is not a good economic solution.
2. Reboring does not remove fatigue damage even though it may remove the heat checks.
3. It is very difficult to avoid running brake drums over the maximum brake face diameter.
4. Martensite (hot spots) and distortion caused by it are virtually impossible to remove.
5. Severe corrosion is frequently on the outside of the drum which weakens the drum.
NOMINAL DIAMETER
MAXIMUM BRAKE FACE DIAMETER
Inches
mm
Inches
mm
7.25
185
7.340
186.44
8.00
204
8.090
205.49
9.50
242
9.590
243.59
9.75
248
9.840
249.94
10.00
254
10.090
256.29
11.00
280
11.090
281.69
11.06
281
11.120
282.45
12.00
305
12.090
307.09
12.25
312
12.340
313.44
14.00
356
14.090
357.89
14.50
369
14.620
371.35
15.00
381
15.120
384.05
16.00
407
16.120
409.45
16.25
413
16.370
415.80
16.50
420
16.620
442.15
16.50
420
16.585
421.25
17.00
432
17.120
434.85
17.25
439
17.370
441.20
18.00
458
18.120
462.25
20.00
508
20.120
511.05
20.25
515
20.370
517.40
21.00
534
21.120
536.45