Brake Rotor Machining

Michael Mobile Technician Clinton, Utah Posted   Latest  
Discussion
Braking
Warp
Out Of Parallel
Resin Deposits

This past week I did training for technicians to take the A5 Brakes Test for ASE. In the class most of the technicians and managers stated that they no longer do rotor machining. They stated that it was just not worth the risk of comebacks. Even the company owner liked the idea of replacing rotors because it added more to the ticket. The consensus was that when the rotors are machined and in specs that they easily warp or start pulsating. This observation does not align with what the part manufactures are writing in their articles. I would like to get some solid data on this subject. From the class I have learned that rotors were being cleaned with brake clean. The industry standard is soap and water. They were not adding a non directional surface. They were not breaking in the pads before delivering to the customer. From what I have read, the parts manufacturers are stating that most pulsation is not from warp or out of parallel, it is from uneven distribution of the pad resins on the rotor surface. They also expressed incorrect prep of the rotor and hub surfaces. The corrosion was not being cleaned off before assembly. I believe that if best practices are followed the machined rotors should perform on par with aftermarket replacements. What have you found? 

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Chris Technical Support Specialist
Commack, New York
Chris
 

Using on car machining equipment provides the most true machining possible. The stack up of tolerances of rotor out of true and hub runout can lead to out of spec runout even with new parts. Many technicians feel intimidated by the machining process and typically use the cost of a poor quality rotor to justify replacement. Taking care of your customers is the best way to retain them. Forcing

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Randy Curriculum Developer
Raleigh, North Carolina
Randy
 

Technicians need to understand what causes most pulsation issues. "Warpage" (excessive runout) is commonly blamed but is only the start of the problem. Excessive runout will not cause pulsation by itself if caliper slides are in good condition. The fact that excessive runout causes the pads to contact the rotor in an uneven manor will create excessive rotor wear in those areas, hence creating a

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Bill Technician
Rosetown, Saskatchewan
Bill
 

I feel it would depend on where you live as well as your shops labor rate to an extent. I will offer my opinion, based on my own experiences. I am very familiar with pro-cut on car equipment as well as off car equipment. FNC rotors do not cut well and I feel cutting the outer layer is likely going to get down into inferior material. Even FNC rotors in my area are rotted on the outer edges most

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Randy Curriculum Developer
Raleigh, North Carolina
Randy
 

Agreed that the base condition of the original rotor should be considered first. My shop was in a saltbelt area so we saw a lot of those rotors that you couldn't believe were on the car.

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Rudy Technician
Montebello, California
Rudy
 

Agreed best practices are whats needed. At the shop I am in now ,when I got here 3 years ago,there were quite a few comebacks for pulsation. What I found was that the techs here were not properly mounting the rotors on the lathe,resulting in an uneven cut. They would just continue cutting until the rotor cut evened out. The thinking was that the rotors were not cutting evenly because they were

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Ric Owner/Technician
Hooksett, New Hampshire
Ric
 

We rarely turn rotors these days. By the time we see vehicles that need brake jobs the rotors are very near their life cycle. Add salt and corrosion and it only makes sense to replace them. Proper mounting, cleaning and fastener torquing has led us to a zero comeback rate for vibration and noise. Replacement works for us.

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Martin Instructor
Burnaby, British Columbia
Martin
 

I believe that there are many pros and cons in regard to consideration for machining brake rotors. First, geographic influences such as regions where rotors physically degrade, resulting in heavy corrosion around the non-contact areas and heavy flaking and buildup in the vents, may warrant replacement over service. I have seen many east coast rust belt vehicles brought in from auctions, where

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James Owner/Technician
Pike, Pennsylvania
James
 

We quit machining rotors over ten years ago. The cost of labor vs. new rotor cost and possible comebacks is a no-brainer for us. Clean the hubs and install coated rotors w/premium pads is the way to go for us. Maybe if we did trucks or heavy equipment we would.

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Tim Educator
Québec, Quebec
Tim
 

Have you ever had rotors out of the box have unacceptable parallelism or LRO? We used to have to true up new rotors a lot, even with OEM parts. Then there is the “brake job” itself - a lot of DIY’ers have done this operation and don’t see why it should cost so much to do correctly. Consumer education is the final frontier!

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James Owner/Technician
Pike, Pennsylvania
James
 

Hi Tim "Have you ever had rotors out of the box have unacceptable parallelism or LRO? " Yes, but very rarely and we exchange them along with another set of pads no questions asked. But again for the high line of vehicles we work with we will only use a high quality manufacturer.

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Marlin Technician
Estacada, Oregon
Marlin
 

In-spec OEM rotors which have been correctly machined, washed, and mounted are typically superior to new AM rotors. There are so many variables involved that there are not many solid general statements which anyone is wise to make. One way to lower comebacks is to use low-quality, highly abrasive pads and low-quality rotors, and replace the pads with 25% or more thickness left; this way, wear

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