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

Clint Bowyer Crew Chief Billy Scott Wins Career-First MOOG 'Problem Solver' Award

Billy Scott, crew chief for Clint Bowyer and the No. 15 Maxwell House Toyota Camry, won his career-first MOOG Steering and Suspension “Problem Solver of the Race” Award after Bowyer made a late charge to finish sixth in Sunday’s Cheez-It 355 NASCAR...

Read more...

A New Way To Learn: Bosch Xperience Mobile Tour Comes To Babcox

The Bosch Xperience Mobile Tour made a stop on Aug. 5 at Babcox Media. Editors were invited to experience the simulated virtual workshop, working through a series of real-world vehicle repair problems using Oculus Rift headset technology. Two trucks,...

Read more...

Raybestos Partners With Schwartz Performance To Restore Classic '69 Mustang Fastback

Raybestos has joined forces once again with Schwartz Performance to restore an American icon muscle car: a 1969 Ford Mustang Fastback. “Raybestos and Mustang are the perfect match of history, leadership and innovation. Working with the first-class...

Read more...

Hyundai No-Start, No-Crank Condition Due to Gear Selector Range Switch

Affected Models: Tucson (2010-); Santa Fe (2010-12); Sonata (2011-); Elantra (2013-); Accent (2012-); Azera (2012- ); and Veloster (2013-). Condition: An improperly adjusted or improperly operating inhibitor switch (range switch) may result in...

Read more...

Be Wary of the Fall Maintenance Slowdown

If you think you don’t need to do any more marketing this quarter because you’ve been riding the summer vehicle maintenance wave, think again. While your car count is likely high — due to road trip inspections, oil changes, A/C service and unperformed...

Read more...

Honda Civic: Failed PCMs and CAN System Diagnostics

It’s not unusual for me to get help requests through my e-mail. Sometimes it’s from working technicians, other times it’s from vehicle owners who can’t get their problems solved through professional repair shops. In early 2014, I received one...

Read more...

Identifix Celebrates 50,000 Direct-Hit Subscribers with 50K Giveaway Contest

Identifix, Inc. has reached another milestone: its 50,000th subscriber to Direct-Hit, its award-winning online tool. To commemorate the occasion, the company has launched a contest called the 50K Giveaway. Five Direct-Hit users who submit a Hotline...

Read more...

Liquid Tools: Choose Your Maintenance Chemicals Based On The Application

The shelves in most parts stores are stocked with an abundance of aerosol maintenance products – everything from cleaners to lubricants. The huge selection of products can be overwhelming, leading to confusion about which product you should purchase...

Read more...

Snap-on Franchisee Conference Draws Record Crowd

Snap-on reports that it drew a record-setting crowd for its Snap-on Franchisee Conference (SFC) held in Washington, D.C., this year. The three-day business conference brings together Snap-on Tools franchisees for insight, information and celebration...

Read more...

Aftermarket TPMS Sensors and Scan Tools

Aftermarket TPMS Solutions Servicing tire pressure monitoring systems (TPMS) can be a quick money-maker that requires minimal labor. The service is also essential since this maintenance applies to every vehicle made or sold in the U.S. since 2008. Manufacturers...

Read more...

Fuel Tank Installation: Avoiding the Second Drop

Nothing is worse than a comeback after a fuel tank has been dropped. Discovering that the fuel tank needs to be dropped again to address a problem can kill shop productivity and profitability. Below are tips that can help you avoid comebacks and dropping...

Read more...

Correct Fuel Hose Installation

Understanding the Differences Between Fuel Hoses Fuel hoses are not universal. Outside of the dimensional requirements, fuel hoses have requirements for permeation, pressure and the type of fuel they can carry. This can get even more confusing when...

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

  • DIY mechanic

    Can you get a pulsating sensation from rear disk brakes?

    • me

      Yes ,even if you have drum brakes.I had my rear spring set go(corroded),and the rear brake shoe came loose and rested on the drum when I drove and Pulsated when I put on the brakes,also made the drums extra hot,as the brake shoe was constantly rubbing on the drum when I drove,even when NOT applying the brakes.

Latest articles from our other sites:

Fall Into Savings With 
The Popular Monroe Shocktober Promotion

The Monroe Shocktober promotion is here for September and October, enabling consumers to get four qualifying Monroe or Rancho shocks or struts for the price of three at a participating vehicle service...More

Patented TRIO Arms Now Standard On Rotary Lift SPOA10 Two-Post Lift

Rotary Lift's SPOA10 two-post lift has been upgraded with exclusive new arms that make the lift even more versatile and easy to use. Rotary Lift’s patented TRIO Arms are now standard on the SPOA10TRIO...More

Hyundai No-Start, No-Crank Condition Due to Gear Selector Range Switch

Affected Models: Tucson (2010-); Santa Fe (2010-12); Sonata (2011-); Elantra (2013-); Accent (2012-); Azera (2012- ); and Veloster (2013-). Condition: An improperly adjusted or improperly operating...More

How to Test Drive a Car to Check for Problems

Test Drive Diagnostics Test drives on the surface can seem like one of the most unprofitable tasks a technician can perform. But, test drives can be one of the most profitable processes a shop can do...More

Patented TRIO Arms Now Standard On Rotary Lift SPOA10 Two-Post Lift

Rotary Lift's SPOA10 two-post lift has been upgraded with exclusive new arms that make the lift even more versatile and easy to use. Rotary Lift’s patented TRIO Arms are now standard on the SPOA10TRIO...More

New Series Of 1/2” Metal Impact Wrenches From Chicago Pneumatic

Chicago Pneumatic has launched a new series of CP7736 1/2” metal impact wrenches, to deliver more durability, power and user comfort for tire changing or general mechanic applications. The compact...More

Aftermarket TPMS Sensors and Scan Tools

Aftermarket TPMS Solutions Servicing tire pressure monitoring systems (TPMS) can be a quick money-maker that requires minimal labor. The service is also essential since this maintenance applies to every...More

Fuel Tank Installation: Avoiding the Second Drop

Nothing is worse than a comeback after a fuel tank has been dropped. Discovering that the fuel tank needs to be dropped again to address a problem can kill shop productivity and profitability. Below are...More