Friction material replacement does not require rotor reconditioning unless other justifications exist. Monroe® recomends rotor reconditioning if they exceed factory specifications in 1) lateral run-out, 2) thickness variations, 3) have a groove in excess of .060 inch. It is not necessary to replace rotors in axle sets. However, when replacing or reconditioning a rotor due to the existing conditions, you may suggest reconditioning of the other rotor on the same axle to eliminate uneven braking behavior. Determine the need to replace based upon the individual rotor conditions that follow. Reconditioning is defined as machining and block sanding, or block sanding only. Block sanding is defined as using 120-150 grit sandpaper with moderate to heavy force for 60 seconds per side. Monroe® recommends a non-directional (swirl) finish that creates a surface roughness (Ra) that meets the OE standard. Always wash rotors after servicing or before installing. (See disc rotor washing).
Disc Rotor Lateral Run-OutDisc rotor lateral run-out is defined as the measurement of deviation of a surface from its plane. This measurement needs to be taken with a dial indicator in the appropriate manner. Any excessive run-out needs to be corrected, but not necessarily through rotor reconditioning. Disc rotor lateral run-out should be checked during the inspection process and confirmed, once the rotor is replaced on the vehicle. Do not recondition new rotors unless they are being pressed or bolted onto an existing hub.
Disc Rotor WashingThe quality of today's drums and rotors require removal of any and all dust, particles and/or residues. Residual contaminants may be present from reconditioning or shipping. Monroe® recommends removing contaminants with detergent, warm water and a clean cloth. CAUTION: Shop towels are chemically treated and may leave a residue that will result in glazing.
| Condition | Code | Procedure |
|---|---|---|
| Corrosion affecting structural integrity | A | Require replacement |
| Examples of severe corrosion are: composite plate separated from friction surfaces and cooling fins cracked or missing. | ||
| Cracked | B | Require replacement |
| Hard spots | 2 | Suggest reconditioning or replacement of rotor according to OEM specifications |
| Lateral run out (wobble) exceeds OEM specifications | B | Require re-indexing, reconditioning, or replacement according to specifications |
| Measured thickness is less than OEM discard specifications | B | Require replacement |
| Rotor thickness is less than OEM "machine to" specifications but thicker than "discard at" specifications, and rotor does not require reconditioning | 1 | Suggest replacement |
| Only applies to vehicles for which OEM "machine to" specifications exist. If OEM does not supply "machine to" specifications, the rotor may be worn to discard specifications. | ||
| Rotor thickness will be less than OEM "machine to" specifications after required reconditioning | B | Require replacement |
| If OEM does not supply "machine to" specifications, you may machine to discard specifications. | ||
| Surface is rust-pitted | B | Require reconditioning or replacement of rotor according to OEM specifications |
| Surface is scored | B | Require reconditioning or replacement of rotor according to OEM specifications |
| Scoring is defined as grooves or ridges in the friction contact surface. Some vehicle manufacturers require machining when scoring exceeds their allowable specifications. | ||
| Thickness variation (parallelism) exceeds OEM specifications | B | Require reconditioning or replacement of rotor according to OEM specifications |
| A | Part no longer performs intended purpose |
| B | Part does not meet a design specification (regardless of performance) |
| C | Part is missing |
| 1 | Part is close to the end of its useful life (just above discard specifications, or weak; failure likely to occur soon, etc.) |
| 2 | To address a customer need, convenience, or request (to stiffen ride, enhance performance, eliminate noise, etc.) |
| 3 | To comply with maintenance recommended by the vehicle's Original Equipment Manufacturer (OEM) |
| 4 | Technician's recommendation based on substantial and informed experience |
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