Brake Drum Refinishing Out of Round, Tapered
Cracked, Scored, or Grooved Drums
An out-of-round or tapered brake drum can cause the following symptoms:
| • | Inaccurate brake shoe adjustment |
| • | Excessive wear on other brake parts because of eccentric action |
| • | Severe and irregular tire tread wear |
| • | Pulsing brake pedal |
Out-of-round and taper can be measured accurately with an inside micrometer and extension rods. The drums should be refinished if taper or out-of-roundness exceeds 0.015 mm (0.006 in).
- Measure the drum inside diameter at the inner edge of the machined braking surface.
- Measure the drum inside diameter at the outer edge of the machined braking surface.
- Record the measurements.
- Repeat steps 1 and 2 at two or more places around the drum.
- When the brake drum exceeds the specification limits in taper and/or out-of-round, refinish the drum.
Brake Drum Refinishing Refinishing, Balance
When refinishing a drum, remove only enough metal in order to obtain a true, smooth braking surface. If the drum does not match specifications after being refinished to the maximum refinish diameter, replace the drum. Refer to Component Specifications . Removal of more metal affects heat dissipation. This will cause brake drum distortion.
All brake drums have a maximum diameter. This is not a refinish diameter. Do not refinish a brake drum that will not meet the specifications. Replace the brake drum. Refer to Component Specifications .
When you refinish a brake drum, resurface the drum to a dimension no more than 0.76 mm (0.030 in) 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 wear.
Always use sharp cutting tools or bits. Dull or worn tools leave a poor surface finish. A poor surface finish will affect initial braking performance. Always use vibration dampening attachments when you refinish braking surfaces. These attachments eliminate tool chatter so that you can obtain a better surface finish.
Follow the manufacturer's instructions and recommendations for setting up and refinishing brake drums.
Crossfeed for rough cutting should range from 0.15-0.25 mm (0.006-0.010 in) per revolution. Make finish cuts at crossfeeds no greater than 0.05 mm (0.002 in) per revolution.
New Replacement Drum Refinishing
Do not refinish the braking surface when installing new brake drums. These parts already are at the correct level of surface finish.
Balance
Manufacturers use weights to balance brake drums. Do not remove these weights.
Check the drums for balance in the following situations:
| • | After refinishing the brake drums |
| • | When maintaining wheel balance is difficult |
Check the drums on off-vehicle balancers. Replace the drum if it is out of balance.
Brake Drum Refinishing Cracked, Scored, Grooved
Important: Do NOT refinish the brake drums in order to correct any of the following
complaints:
• Brake noise (growl/squeal) • Premature brake lining wear • Cosmetic or superficial corrosion of the drum braking surface • Drum discoloration • Severe scoring of the drum braking surface (groove depth in excess
of 1.5 mm (0.060 in) • Brake pulsation caused by the following: - Brake drum out of round - Corrosion or pitting that is deeper than the drum braking surface
The Accu Turn® or Ammco® brake lathe is approved and achieves satisfactory results.
- Remove the tire and wheel. Refer to Wheel Removal in Tires and Wheels.
- Make a mark on the brake drum in order to identify the relationship to the axle flange.
- Remove the brake drum.
- Use a micrometer in order to measure the largest diameter of the brake drum. If the largest diameter of the brake drum exceeds the brake drum maximum refinish diameter, do NOT refinish the brake drum. Replace the brake drum. Refer to Component Specifications .
- Use the J 41013 Resurfacing Kit (or equivalent) in order to THOROUGHLY clean the rust from the brake drum flange.
- Install the brake drum to the brake lathe. Refer to the brake lathe manufacturer's operating instructions.
- Refinish the brake drum. Refer to the brake lathe manufacturer's operating instructions.
- After machining the brake drum, use 120 grit aluminum oxide sandpaper in order to create a non-directional braking surface.
- Clean the braking surfaces with denatured alcohol or with a suitable brake cleaner.
- Remove the brake drum from the brake lathe.
- Install the brake drum to the vehicle. Align the brake drum to the hub using the marks made during the removal procedure.
- Install the tire and wheel. Refer to Wheel Installation in Tires and Wheels.
Important: Failure to obtain the best possible braking surface finish may cause the vehicle to stop with difficulty.
Notice: Improperly tightened wheel bolts or nuts can lead to brake pulsation and rotor damage. In order to avoid expensive brake repairs, evenly tighten the wheel bolts or nuts to the proper torque specification.
