Tech Tip: Lower Mass Brake Rotor Causing Noise, Fade and Failure Problems – UnderhoodService

Tech Tip: Lower Mass Brake Rotor Causing Noise, Fade and Failure Problems

If a customer complains of noisy brakes, increased stopping distances and pedal pulsation after brake rotors were replaced or machined, the rotors may be the source of the problem. It's easy to blame the pads or brake hardware, but technicians need to look at the rotor. Affinia Global Brake & Chassis discovered during a recent benchmarking study of the competition that some rotor companies have reduced their ....

Application: All vehicles

Symptoms: Glazed pads, heat checking and cracking of the rotor, and brake noise.

Cause: Rotors with reduced weight and plate thickness, and improper vane configuration.

Condition: If a customer complains of noisy brakes, increased stopping distances and pedal pulsation after brake rotors were replaced or machined, the rotors may be the source of the problem. It’s easy to blame the pads or brake hardware, but technicians need to look at the rotor.

Affinia Global Brake & Chassis (manufacturer of Raybestos Brand Brakes and rotor supplier to NAPA and ACDelco) discovered during a recent benchmarking study of the competition that some rotor companies have reduced their plate thickness by expanding the air gap and reducing the weight of their vented rotors. The study revealed that rotor mass for some rotors was reduced by 7- to 24-percent. On applications such as GM full-size trucks, Affinia Global Brake & Chassis reported a weight reduction of 5-lbs., from 26 lbs. to 21 lbs., when compared to the OE part.

In addition to increasing the air gap to reduce weight, other changes were discovered, including different vane configurations and materials used to cast the rotor. The reduction in vane mass causes material strength to decrease at the vane/surface plate interface and can lead to the possibility of failure. These changes can reduce costs and do not conform to OE specifications.

Brake rotors are safety-related components and should never be compromised. Less mass means decreasing the heat resistance of the rotor. Heat energy that flows into the rotor is inversely proportional to thermal resistance to conduct heat flow. By reducing the mass it increases thermal resistance, causing the rotor to become hotter during operation. This will result in brake fade, “warpage,” pedal pulsation, rotor cracking, uneven friction wear, material transfer and reduced friction pad life. Also, if the rotor is not able to absorb and dissipate the heat, the system will run hotter and the extra heat is transferred to the pads, caliper piston and eventually the brake fluid, ultimately resulting in brake fade, increased pedal travel and longer stops.

These “low mass” or “lightweight” rotors can also cause noise problems. The plates and vanes of an OE rotor are tuned specifically for the vehicle to absorb or dampen noise and vibration.

If you are machining a rotor on a lathe, look at the thickness of the rotor’s plates. Rotors with thinner plates have less material on the plates to machine. Even if the rotor is above the discard specifications, the rotor may not be safe to put back on the vehicle.

If you do encounter a situation where noise has caused a comeback, follow the below procedure:

Inspection and Repair Procedure:

1. Examine the rotor for signs of heat checking and cracking. Make sure to check the collar (area where the hub meets the plate) and the outer edge. If any cracks or mechanical damage are found, the rotor must be replaced.

2. Compare the thickness of the rotor plates to an OE or premium-quality rotor. If possible, weigh the rotor on a scale and compare. If the weight and plate thickness are significantly below the OE or a premium-quality rotor, replace the rotor.

3. Measure runout in the rotor and wheel bearing with a dial indicator. Also, check the thickness of the rotor with a micrometer. On most vehicles, lateral runout greater than 0.002” will generate a pulsation complaint.

Note: If a new rotor is installed, it is not necessary to machine the rotor.

4. Inspect the caliper piston boots for heat damage. The material should be defect-free and pliable. The boots can be damaged by the elevated temperatures and will even catch fire. Any damage to the boot will cause an increased rate of wear to the caliper seal. Replace the damaged boot or caliper, if necessary.

5. Reassemble the caliper and bracket. Lubricate all slides, pins and hardware with the appropriate lubricant.

6. Replace the brake pads if they are glazed or show other signs of other mechanical damage like edge lift. Often, the extreme heat will change the chemical structure of the friction material and cause it to separate from the backing plate.

7. Test-drive the vehicle. If new pads were installed, perform the manufacturer’s recommended break-in procedure.

Courtesy of Affinia Global Brake & Chassis.

For more information about Raybestos brand brakes, visit www.raybestos.com.

You May Also Like

VIDEO: AAPEX 2016 Insights

Andrew Markel discusses his take on conversations he had with economists at AAPEX 2016, including the future of purchasing parts.

Andrew Markel discusses his take on conversations he had with economists at AAPEX 2016, including the future of purchasing parts.

BMW Tech Tip: Oil Separator Replacement

A clogged oil separator valve is a common problem on many BMW DOHC inline sixes. The high failure rate is caused by sludge build-up that can result in oil burning, rough idle and engine fault codes. Although the solution is pretty simple, replacing the valve is labor intensive and can take anywhere from six to nine hours.

New IDUSA Premium Guard Website Offers Easy Access To Wide Range Of Oil, Air, Cabin, Fuel And Transmission Filters

The new website’s bi-lingual, responsive design features look-up powered by ShowMeTheParts.

VIDEO: How To Deal With Air Conditioning Smells

Andrew Markel discusses what to do to get rid of A/C smells after customers have tried to do it themselves.

Oil Bath Air Filters

Long before people started using cotton gauze air filters soaked in oil, the oil bath air filter was the dominant filter on the market. The filter removes debris in the air by running it over oil and a mesh element. These filters worked great when most roads were dirt, but they could be messy to clean.

Other Posts

On The Web – September 2016

Finding Failing O2 Sensors If an O2 sensor gets “lazy” because of old age or contamination, the computer may not be able to adjust the fuel mixture quickly enough as the engine’s operating conditions change. Related Articles – Join Underhood Service On LinkedIn – Honda Tech Tip: Oil Pressure Switch Fails Intermittently – Fuel Trim

Join Underhood Service On LinkedIn

Related Articles – Check Out The August Issue Of Underhood Service Magazine – Hayden Automotive Introduces Low-Profile Fan Clutch – Belt Inspection Checklist                     Underhood Service’s LinkedIn Page                         Underhood Service’s LinkedIn Group    

Honda Tech Tip: Oil Pressure Switch Fails Intermittently

The MIL comes on with one of these DTCS: P3400 (VPS Stuck Off Bank 1) or P3497 (VPS Stuck Off Bank 2). This may be the result of the front and/or rear rocker arm oil pressure switch intermittently failing.

Fuel Trim And AFR Sensors

Fuel trims are a difficult topic to cover in a matter of a few pages. But this summer, an old friend and former teaching partner arrived at our local car show with the check engine light illuminated on his 2004 Holden Monaro, which was imported from Australia and rebadged and sold in the U.S.