C 2500 Truck 2WD V8-305 5.0L VIN M SFI (1997)
Brake Drum: Service and Repair
Refinishing Drums
Used Drum
If you determine a drum needs refinishing, remove only enough metal to obtain a true smooth braking surface. If a drum does not clean up when
refinished to the maximum refinish diameter as shown in Specifications, replace it.
All brake drums have a maximum diameter cast into them. This diameter is the maximum wear diameter and not a refinish diameter. Do not refinish a
brake drum that will not meet specifications; instead, replace it.
When refinishing a brake drum, resurface the drum to a dimension no more than 0.76 mm (0.030 inch) less than the discard diameter. The refinish
diameter is the maximum diameter the drum can be refinished to and still allow safe braking action. If you exceed this diameter, the brake drum will
wear beyond the discard diameter during normal brake use.
Always use sharp cutting tools or bits. Dull or worn tools leave a poor surface finish that will affect initial braking performance. Always use vibration
dampening attachments when you refinish braking surfaces. These attachments eliminate tool chatter so you can obtain a better surface finish.
The best speed for refinishing braking surfaces is a spindle speed of 150 rpm. Cross feed for rough cutting should range from 0.15 to 0.25 mm (0.006
to 0.010 inch) per revolution. Finish cuts should be made at cross feeds no greater than 0.05 mm (0.002 inch) per revolution.
New Replacement Drum
When installing new brake drums, do not refinish the braking surface. These parts are already at the correct level of surface finish.
A new drum must have the protective coating removed from the friction surface before being placed in service. Use Goodwrench brake parts cleaner
GM P/N 12345754 or equivalent and wipe the surface clean with clean cloths. Do not use gasoline, kerosene, or other oil base solvents that can leave
an oily residue. This residue is damaging to brake linings and flammable.
Balance
During manufacturing, weights are used to balance brake drums. Do not remove these weights.
After you refinish brake drums or whenever a persistent wheel balance problem occurs, check the drums for balance. They can be checked on most
off-vehicle balancers. If found to be out of balance, replace the drum.
NOTE: Any time you remove the brake drums, thoroughly clean and inspect them for cracks, scores, deep grooves and out-of-round.
NOTE: If the drum is grooved and the linings are slightly worn, the drum should not be machined. Instead, polish the drum braking surface with fine
emery cloth. Eliminating all of the drum grooves and ridges on the lining would require removing too much metal and lining material. When grooves and
ridges match, satisfactory brake service can be obtained by leaving them alone.
