Rotor Refinishing

CAUTION: Servicing of disc brakes is extremely critical due to the close tolerances required in machining the brake disc to insure proper brake operation.


Tolerance and Precision
The maintenance of these close controls on the friction surfaces is necessary to prevent brake roughness.

In addition, the surface finish must be non-directional and maintained at a micro-inch finish.
- This close control of the rubbing surface finish is necessary to avoid pulls and erratic performance and promote long lining life and equal lining wear of both left and right brakes.


In light of the foregoing remarks, refinishing of the rubbing surfaces should not be attempted unless precision equipment, capable of measuring in micro-inches (millionths of an inch) is available.


Resurfacing Braking Disc
This operation can be used when the disc surface is rusty or has lining deposits. A sanding disc attachment will remove surface contamination without removing much material. It will generally follow variations in thickness which are in the disc.

Fig 2 Refacing Brake Disc:

Refacing Braking Disc
Rotors do not have to be refaced every time a disc brake is relined.
- If the rotor surface is deeply scored or warped or there is a complaint of brake roughness the rotor should be refaced.

When refacing a disc brake rotor the required TIR (Total Indicator Reading) and thickness variation MUST BE MAINTAINED.

CAUTION: If the disc is not mounted properly the runout will be worse after refacing than before refacing. Extreme care in the operation of rotor turning equipment is required.
- The use of a double straddle cutter which machines both sides of the disc at the same time is mandatory.
- When mounting the disc on the lathe strict attention to the manufacturer's instructions is required.
- The collets, shafts and adaptors on the lathe and the bearing cups in the rotor MUST be clean and free from any chips or contamination.

Fig 3 Disc Measurement Points:

DO NOT reface a disc brake rotor more than 0.030 inch less than the original disc minimum thickness. Reface both sides of rotor, not exceeding 0.030" total.

All rotors (disc) will show marking of minimum allowable thickness cast on the un-machined surface. This marking includes 0.030 inch (0.762mm) allowable rotor wear beyond the recommended 0.030 inch (0.762mm) of disc refacing.

Example:
- Minimum Allowable Thickness 0.940 (23.8mm)
- Allow for Wear 0.030 (0.762mm)
- Do Not Reface Beyond 0.970 (24.6mm)