AfterMarketNews AfterMarketNews Auto Care Pro AutoCareCareerHub Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

No More Free Tire ­Rotations!

Tire rotation is a cornerstone of vehicle preventive maintenance and tire longevity. It is a well-proven fact that tire tread life can be greatly enhanced by regular and timely tire rotation. During rotation, each tire and wheel is ­removed from...

Read more...

ASE G1: How To Measure Cold Cranking Amps, Reserve Capacity

The ASE G1 test contains 55 scored, job-related questions, 15% of which will concern electrical maintenance and repairs. From the ASE G1 study guide, you will need to know how to: • Perform battery tests (load and capacitance); ­determine needed...

Read more...

ASE A5: Brake Fluid And Bleeding Sequence

The ASE A5 Test includes a portion on brake fluid, bleeding, flushing and leak testing. You must know how to: • Diagnose poor stopping, pulling, dragging, or incorrect pedal travel caused by problems in the brake fluid; determine needed repairs. •...

Read more...

Modern Charging Systems: Cover All The Bases During the Diagnostic Process

To quote a familiar situation: “My customer’s car is now on its third alternator in six months and my jobber store refuses to ­warranty a fourth.” In other words, the parts supplier believes that an underlying problem is causing these alternators...

Read more...

Audi Fuel System: MIL On/Multiple Low Fuel Pressure DTCs

Due to fuel intrusion into the low-pressure ­system fuel pressure sensor (G410), a false signal may be sent to the controller, resulting in a reading that is out of tolerance. Model: 2007 Audi A4 Sedan V6-3.2L Scenario: The MIL is on and one or...

Read more...

Toyota: Check Engine Light Leads To New Battery Temperature Sensor

Complaint: The customer states the check engine light is on. Cause: A scan tool finds code P0517 – Battery Temperature Sensor Circuit High. A road test, while using the scan tool to ­monitor live data, finds the battery temperature sensor signal...

Read more...

Top 5 Tools: John Forro, AST, Automotive Service Technology in Hinckley, OH

John Forro AST, Automotive Service Technology Hinckley, OH ALLDATA Information System: I use this system daily for researching labor pricing, wiring schematics, circuit descriptions, torque specs, etc. One doesn’t need to memorize all the information...

Read more...

Phoenix Systems And NAPA Announce New Retail Agreement

Phoenix Systems has announced an agreement with NAPA/Balkamp to put Phoenix Systems products in their stores. As part of this agreement, NAPA locations will now have access to BrakeStrip Brake Fluid Test Strips and the New NAPA Service Tool 2104-B Reverse...

Read more...

MAHLE Service Solutions Unveils New Website

MAHLE Aftermarket, Service Solutions, formerly MAHLE RTI, has introduced its new website at www.servicesolutions.mahle.com. The site contains updated information on MAHLE Aftermarket’s newest division, providing visitors with a clean, user-friendly...

Read more...

Must-Read TPMS Technical Service Bulletins

Here’s a rundown of the top technical service bulletins related to TPMS. These TSBs should be analyzed by every technician that services TPMS. Audi TSB Number: 4413382034445/1 Models: 2010-’14 A4/S4, A5/S5 and Q5 Summary: This TSB addresses TPMS...

Read more...

Ford Reflash: Setting Up Your PC

You’ve just finished up a job on a Ford vehicle, and you’re about to try and start it up. However, it needs programmed first. You’ve decided to use a J2534 tool, but there are certain things you’ll need to consider ­before purchasing that subscription...

Read more...

Fuel Line Replacement: The Why and How

If you live in a state that doesn’t get snow, you can stop reading right now. If you live in the Snow Belt, you are about a month away from snow and ice. It’s not the adverse driving conditions that should scare you or your customers, it’s...

Read more...

Home Brakes Brake Pulsation Questions, Rotors, DTV

Print Print Email Email

Answered by the editors of BRAKE & FRONT END

1. What causes runout?

Rotor runout can be caused by several things: variations in manufacturing tolerances, sloppy resurfacing procedures, a buildup of rust and corrosion between the rotor, hub and wheel, and uneven torque on the lug nuts.

2. What else can cause pulsation problems besides the rotors?

Loose wheel bearings will cause the rotor to tilt in the caliper when a load or side thrust is placed on the bearings. Disc brake pistons require lots of fluid volume and pressure to push the pad against the rotor. If loosely adjusted wheel bearings force the pistons into the caliper, the result will be a low or spongy brake pedal.

3. What exactly is “pulsation” and how does it relate to “warping?”

If a vehicle equipped with floating or sliding calipers has a slider problem which prevents the caliper housing from moving, runout can cause pulsation. The caliper piston will move in and out as the rotor rotates resulting in fluid movement and pedal pulsation. Likewise, fixed caliper vehicles are sensitive to runout induced pedal pulsations. Fixed calipers have pistons on both sides of the rotor due to the stationary caliper housing. Excessive runout will cause piston movement and can result in pedal pulsation due to the runout.

4. What else can cause customers to think their rotors are warped?

Brake roughness is the other component to the equation and it is often misinterpreted and misdiagnosed problem. At the root of brake roughness is a characteristic called Brake Torque Variation (BTV). This can be determined by measuring torque multiple times within one wheel revolution. The brake torque variation is the maximum torque measured within one revolution subtracting the minimum measured.

If BTV is excessive, the vehicle will start to transmit the BTV back to the driver and generate a comeback. The symptoms are pulsation in the pedal.

5. What is Disc Thickness Variation?

People generally equate a high runout value with “warping.” In reality, runout by itself is not a direct or sole generator of pulsation. The characteristic that most directly generates roughness is actually Disc Thickness Variation (DTV). This measurement is the result of measuring the thickness of the rotor surface at multiple spots around the rotor.

The DTV is the largest (thickest spot) minus the smallest (thinnest spot) of the rotor. This action of thick and thin spots passing through the caliper generates the brake torque variation. When the thick part of the rotor is forcing itself through the caliper, the torque of the brake and the pressure in the caliper rise. When the thin spot passes through, the torque drops and pressure drops. Very small amounts of DTV can create a significant problem. Today, new vehicles are typically built with a thickness variation of less than 0.00078”. Thickness variations in excess of 15 microns (0.00059”) can easily generate driver complaints.

6. “Do I have to measure the runout for every brake job? I don’t have the time!”

The bigger question is, “Do you have time for comebacks?” A dial gauge is used to measure runout in the rotor and hub assembly.

The dial gauge is a very robust piece of equipment that can last a lifetime. It is also a good idea to invest in a good magnetic base or vise-grip handle that can be setup quickly.

Always use a dial indicator to verify the amount of runout present in a rotor and hub assembly, both before and after the rotors have been machined. This must be performed even if you are using an on-the-car lathe. By measuring the rotor on the hub, you can also check for play in the wheel bearings, corrosion on the mounting surface and other possible errors. Even if you are putting new rotors on a vehicle, runout should be checked. It doesn’t take much, only about .002 inches on some vehicles, to cause a noticeable pulsation. Also, if you are using a bench lathe, the dial indicator can be used to check to see if you have mounted the rotor or drum properly to the lathe.

7. I drove the vehicle after the brake repair and there was no pulsation problem. What caused the customer to comeback after a few thousand miles with a pulsation problem? Is their braking technique at fault?

Ninety-eight percent of the time, pulsation complaints are not the fault of the driver. The cause of the DTV/Runout and resulting pulsation is a product of the interaction of the rotor and pads over time and how the caliper interprets the runout. But, the main reason why the customer is back is that the runout was not measured in the hub.

The vehicles most susceptible to reoccurring pulsation are those that use unitized bearings. Unitized bearings are preloaded and have zero play. No wheel bearing play results in the runout being “seen” by the brake pads with every revolution of the rotor. The resulting high and low spots scrape the brake pads with every revolution of the rotor. This scraping occurs during not only during braking, but also non-braking.

The long-term result of this scraping is the DTV. Pedal pulsation is the symptom of excessive DTV. The alternating thick and thin spots of the rotor cause the caliper piston to move in and out as the brakes are applied. The caliper piston moves out on the thin spots and in on the thin spots. The piston movement causes brake fluid to move in the hydraulic system and results in corresponding brake pedal movement in the form of a high-speed pedal pulsation.

8. There is not any runout in the rotor, but the customer is still complaining of a pulsation problem. What could it be the cause?

The problem might not be the brake rotors, but the pads. If the brake system is used to the intended limits and the brake pads go beyond their operational temperature limit they will deposit brake pad material unevenly on the brake rotor. Pad material build up creates uneven rotor thickness, which gives you the sensation of a “warped” brake rotor.

Try switching to a more robust brake pad, and clean up the rotors with a light pass on the lathe.

9. Volcanic Bearings?

Many bearings will actually have a machined step in the region the wheel studs are installed. This masks the localized “volcanoing” that occurs in the material around the stud. This micron (1 micron = .000039”) level volcanoing will distort the rotor when the clamp load of the wheel is applied.

10. Will a non-directional finish reduce the chance of a comeback for pulsation problem?

In theory, a non-directional finish will help to burnish the brake pads more effectively. For some friction materials, the non-directional finish will help to deposit a thin layer of friction material on the rotor’s surfaces.

According to GM… In technical bulletin #00-05-22-002 to its dealers, GM says:

“Brake rotors should only be turned when one of the following rotor surface conditions exist: severe scoring with depth in excess of 1.5 mm or 0.060 inch, pulsation from excessive lateral runout of more than .080 mm or .003 inch, thickness variation in excess of 0.025 mm or 0.001 inch, or excessive corrosion on rotor braking surfaces.”

Lug nut torque is also extremely important. Under-torquing only a single lug nut may create as much as 0.003-inch of lateral runout in a rotor!

.0015 inch or less of lateral runout is needed on the rotors to prevent pedal pulsation. If runout is excessive, try indexing the rotor on the hub to see if a change in position helps. Tapered steel shims are also available, or use an on-the-car lathe to cut the rotors in place.

The following two tabs change content below.
Brake and Front End Staff

Brake and Front End Staff

  • DIY mechanic

    Can you get a pulsating sensation from rear disk brakes?

Latest articles from our other sites:

Browse CARDONE's Fall Parts Guide

CARDONE says that the company's new fall parts guide highlights new products like the new CARDONE Ultra premium line of calipers and other hard-to-find parts. The guide also features links to several new...More

ASA/AASA Safety Inspection Forum Reveals Widespread Support For Vehicle Inspection Programs

On Friday, Nov. 14, the Automotive Service Association (ASA) and the Automotive Aftermarket Suppliers Association (AASA) hosted a Vehicle Safety Inspection and Maintenance Forum in East Norriton, Pa. Forum...More

Modern Charging Systems: Cover All The Bases During the Diagnostic Process

To quote a familiar situation: “My customer’s car is now on its third alternator in six months and my jobber store refuses to ­warranty a fourth.” In other words, the parts supplier believes...More

Audi Fuel System: MIL On/Multiple Low Fuel Pressure DTCs

Due to fuel intrusion into the low-pressure ­system fuel pressure sensor (G410), a false signal may be sent to the controller, resulting in a reading that is out of tolerance. Model: 2007 Audi A4 Sedan...More

MOTOSHOP Technology Tools Adds Subaru To MotoLOGIC Repair & Diagnostics

MOTOSHOP Technology Tools announced the addition of Subaru info to MotoLOGIC Repair & Diagnostics, a Web-based tool for automotive technicians. The addition of OE repair and diagnostics information...More

OptiCat LLC Announces 'OnLine Parts Research Catalog'

OptiCat has announced the launch of its new OptiCat OnLine parts research catalog, located at www.opticatonline.com. OptiCat OnLine allows suppliers, WDs, professional repair shops and consumers a high-quality...More

Must-Read TPMS Technical Service Bulletins

Here’s a rundown of the top technical service bulletins related to TPMS. These TSBs should be analyzed by every technician that services TPMS. Audi TSB Number: 4413382034445/1 Models: 2010-’14 A4/S4,...More

ASE G1: How To Measure Cold Cranking Amps, Reserve Capacity

The ASE G1 test contains 55 scored, job-related questions, 15% of which will concern electrical maintenance and repairs. From the ASE G1 study guide, you will need to know how to: • Perform battery...More