Brake rotor warping

Ryan Mechanic Edmonton, Alberta Posted   Latest  

I have been at this career for almost twenty years now. Since the beginning I was told by the journeymen that a pulsating brake pedal meant that the brake rotors were warped. I was even taught this in trade school. Only when I stumbled across an article on the subject a couple of years ago did I learn of this widespread mistake. Brake rotors don't warp.

Rather than try and explain it, I'll just post a link to the article.

stoptech​.​com/technical-supp…

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Thomas Technician
Manassas Park, Virginia
Thomas
 

Now here is my question because at my current place of work my coworkers and I debate on this, you find a vehicle that was excessive run out, do you replace both the brake pads and rotors or do you turn the rotors and if there is plenty of friction material keep the same brake pads on after you have cut the rotors? Now from what I have been taught from my last job when i started in this field

+1 Ð Bounty Awarded
Ryan Mechanic
Edmonton, Alberta
Ryan
 

A hard pad will give you thickness variation on the rotor. This is because it wears the rotor down. A soft pad will leave deposits on the rotor. As long as there was adequate brake material left I would leave the pads as they aren't the issue.

0 Ð Bounty Awarded
Michael Mobile Technician
Clinton, Utah
Michael
 

Hi Ryan, That article is very interesting. It explains how a brake job can go bad right out of the gate. Proper break in for the customer is something most techs do not do. Taking a test drive eats into the flat rate. So far we don't add time for test drives. Maybe it is time we do. Over the last few months I have been training a multi store chain. We are doing ASE prep. The common attitude of

+3 Ð Bounty Awarded
Ryan Mechanic
Edmonton, Alberta
Ryan
 

Exactly. A few more minutes at the job will prevent future comebacks. I have always been a fan of the on car brake lathes. Your run out is bang on every time.

+1 Ð Bounty Awarded
John Instructor
Beaver, Pennsylvania
John
 

We had to learn the hard way that cooling fin corrosion inside the rotors creates varying heat ranges in the rotor under heavy use which is the source of a lot of brake pulsation conditions. If not that the other cause is delamination. Those two conditions combined in the rust belt make machining rotors a poor choice and just asking for a vehicle to have to come back under a warranty repair. So

0 Ð Bounty Awarded
John Instructor
Beaver, Pennsylvania
John
 

It's a good article from a racing perspective but has questionable application from normal vehicle service and repair. For one, it does not take into account corrosion of the rotor surface, and especially the rotor's cooling fins. He is correct about pad material transferring unequally around the surface of the rotor as a cause for brake pulsation, but he never mentions a brake pulsation caused

0 Ð Bounty Awarded
Ryan Mechanic
Edmonton, Alberta
Ryan
 

When I was working in the rust belt, I found that rotors would need to be replaced from surface pitting well before vent rusting was ever an issue.

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John Instructor
Beaver, Pennsylvania
John
 

Totally agree, where techs ran into trouble is when someone else didn't understand the complete scope of the corrosion issue and were told to cut the rotors. Now the cooling fin issue becomes dominant and the tech would get accused of machining the rotor incorrectly when the car returned with another pulsation complaint.

+2 Ð Bounty Awarded