H-27. BRAKE DRUM SERVICE INFORMATION (Cont.)
Turning the Brake Surface (Cont.)
Do not turn or wear a brake drum beyond the maximum diameter stamped
or cast on the brake drum.
B. The maximum diameter or discard diameter is the maximum diameter to which the brake
drum may be turned or worn and still be usable. If any portion of the brake surface exceeds
the maximum diameter it must be discarded. The maximum diameter is 0.120 over the
nominal new diameter unless stated otherwise on the casting. The maximum diameter cast
into the back plate portions of the brake drum supersedes all published information.
Replacement of the brake drum is required if any of the following conditions exist:
1. Brake drum is cracked.
2. The brake surface is heat checked, grooved, or worn beyond the re-bore limit of
0.080, or maximum diameter.
3. The back plate is cracked.
4. The boltholes are elongated.
5. Brake drum is known to have been severely overheated.
6. Brake drum is out -of-round.
When selecting a Webb replacement drum, the manufacturer's name and part number are
helpful. If this information is not available, a replacement drum can be selected by comparing
dimensions. A drawing is shown on page H 70 with the dimensions required to determine the
existence of a replacement drum. If all the dimensions shown are not available, we must have at
least the following dimensions from page H-70 to make a selection:
C. Brake Face Diameter
D. Overall Depth of Drum
E. Brake Surface Flat
J. Bolt Circle Diameter
K. Pilot Diameter
O. Bolt Hole Number and Size
Other Drilling or Special Features