Article: The Warped Brake Disc and Other Myths of the Braking System
- Thread starter Supracentral
- Start date
They can and do warp. And the pads failing to bed properly can literaly melt onto the pad and cause a pulsation in another way.
I will quote from online, since it is a quick refrence for all here.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BR&P=28
I will quote from online, since it is a quick refrence for all here.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BR&P=28
Supracentral;1515714 said:
^^^ Haven't been on in a couple months, the new format looks very sharp Mike, YAY!!
One work truck in my work fleet had new pads incorrectly broken-in.
The vibration causes a feeling of unsure performance.
The driver has the habit of gradually increasing pedal pressure as they approach the intended stopping point.
Hard to break the habits of old dogs
I'll try fitting the metallic pads to see if it helps, as the truck never does hard stops.
One of my first jobs in industry was at a Brake and Clutch manufacturer/repairer, might be of interest to some that you NEVER machine rotors to 0 runout, usually 2 thou is acceptable as it's enough to knock the pads off the rotor in use and stops squeaks/drag/squeal.
The square section o-ring seal in the calliper acts as the return "spring" for the piston but there's no positive connection to the pad so it will contact the rotor if it's been machined to 0 runout.
Most times a pulsating pedal is pickup on the rotor surface.
In machining literally 1000's of discs I rarely saw a "warped rotor" usually if they were they were 9 parts trashed anyway and binned, worst I ever saw was a local govt vehicle that had worn the pads through, worn the backing plates through and had lost 10mm off the pistons as they took the place of the pads.... :nono: HTF do people drive a car like that for so long..
<edit> After reading BHM's post here's another story from back then
Had a woman bring a car in for rotors and pads, normally I'd take the car out bed the new pads and have ot ready for the customer, she didn't have time it was a rush job as she hard to be somewhere....
She takes the car and heads off into peak hour traffic, 15 minutes later we get a frantic call that the car is stuck at a set of lights and won't move no matter what she tries, we send a flatbed the car arrives back at the shop, turns out she's worked the brakes hard enough to boil out some of the resin in the pads and then stopped for a red light and the resin has bonded the pads to the rotors.
half an hour later and an air chisel a quick skim of the rotors and a rebed by me and she was on the road again, her haste/rush cost her an extra hour.
The square section o-ring seal in the calliper acts as the return "spring" for the piston but there's no positive connection to the pad so it will contact the rotor if it's been machined to 0 runout.
Most times a pulsating pedal is pickup on the rotor surface.
In machining literally 1000's of discs I rarely saw a "warped rotor" usually if they were they were 9 parts trashed anyway and binned, worst I ever saw was a local govt vehicle that had worn the pads through, worn the backing plates through and had lost 10mm off the pistons as they took the place of the pads.... :nono: HTF do people drive a car like that for so long..
<edit> After reading BHM's post here's another story from back then
Had a woman bring a car in for rotors and pads, normally I'd take the car out bed the new pads and have ot ready for the customer, she didn't have time it was a rush job as she hard to be somewhere....
She takes the car and heads off into peak hour traffic, 15 minutes later we get a frantic call that the car is stuck at a set of lights and won't move no matter what she tries, we send a flatbed the car arrives back at the shop, turns out she's worked the brakes hard enough to boil out some of the resin in the pads and then stopped for a red light and the resin has bonded the pads to the rotors.
half an hour later and an air chisel a quick skim of the rotors and a rebed by me and she was on the road again, her haste/rush cost her an extra hour.
Stop-Tech web site is extremely informative. Especially the technical white papers on other topics in addition to the "Top Ten Myths" posted above.
The "bedding in" write up is also an excellent read.
I did not see the link in the article you posted so...
http://www.stoptech.com/
The "bedding in" write up is also an excellent read.
I did not see the link in the article you posted so...
http://www.stoptech.com/
Last edited:
Instead of installing different pads i just turned the rotors as the machine shops likes me and only wanted $20 for the rears.
Smoooooooooth like butter, very nice
Smoooooooooth like butter, very nice
if the rotors are being machined back to a true flat surface, (thus removing the uneven deposition of pad material), why does the article say that the problem usually returns very quickly? because the rotors are machined and reinstalled, but the pads are still unevenly worn?
After ten years as a auto mechanic, I have seen, and verified many warped brake rotors. A run out gauge tells the tale. It also can be seen in the machining process, as it makes an uneven first cut when severe. It seems to me, that to base this article on racing use, overlooks the myriad ways people can abuse their brakes in the real world. And BTW, drums can distort too.
"With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc."
So in other words if wheel nuts are not torqued to the right spec and are not uniform, you can in fact have a warped disc. Improperly torquing wheels is fairly common, so why would a warped rotor be so uncommon? Also when machining rotors, taking a light cut, often the bit will only cut a portion of the rotor (the part that sits higher than the rest), and it will show material taken off at opposite ends of the rotor, on opposite sides, if that makes any sense(and the rotor can be dismounted, rotated 180 degrees, remounted, and material comes off the same spots, so it can be confirmed its not a problem in the mounting of the rotor to the machine). I dont see how uneven pad transfer would cause that, if it was uneven pad transfer wouldn't i see random sections of the rotor being shaved off because of random high spots caused by pad transfer?
So in other words if wheel nuts are not torqued to the right spec and are not uniform, you can in fact have a warped disc. Improperly torquing wheels is fairly common, so why would a warped rotor be so uncommon? Also when machining rotors, taking a light cut, often the bit will only cut a portion of the rotor (the part that sits higher than the rest), and it will show material taken off at opposite ends of the rotor, on opposite sides, if that makes any sense(and the rotor can be dismounted, rotated 180 degrees, remounted, and material comes off the same spots, so it can be confirmed its not a problem in the mounting of the rotor to the machine). I dont see how uneven pad transfer would cause that, if it was uneven pad transfer wouldn't i see random sections of the rotor being shaved off because of random high spots caused by pad transfer?
The layer of pad transfer is pretty hard to distinguish from the rotor itself, except for the pad imprint area (if you really messed it up). When you check the rotor for runout with a dial indicator, it is measuring the rotor AND the transfer layer.
Say all you want about the pad transfer thing being nonsense... I have gotten rid of slightly "warped" rotors on at least 30-40 cars by re-bedding the brakes and/or installing new pads and bedding the brakes... WITHOUT replacing or cutting the rotors.
I've even had a few customers that were at their wits end when they came to me because they had their rotors and pads replaced nearly every 3000 miles because the discs kept "warping". They were mostly aggressive drivers, but a few had cars with laughably small brake rotors or cheapo brake pads. I replaced their pads with a set of quality brand "street performance" pads (and the rotors if they were severely overheated) and only ever had one person complain about the slight squeal and slightly less cold stopping power (but never about brake shudder coming back). One of these cars was my own car (went from auto parts store premium pads to "track day" pads on mine to cure the shudder, didn't change or cut the rotors though)
Stoptech knows their stuff.... I've never had problems with any of their tech advice, only good results.
Say all you want about the pad transfer thing being nonsense... I have gotten rid of slightly "warped" rotors on at least 30-40 cars by re-bedding the brakes and/or installing new pads and bedding the brakes... WITHOUT replacing or cutting the rotors.
I've even had a few customers that were at their wits end when they came to me because they had their rotors and pads replaced nearly every 3000 miles because the discs kept "warping". They were mostly aggressive drivers, but a few had cars with laughably small brake rotors or cheapo brake pads. I replaced their pads with a set of quality brand "street performance" pads (and the rotors if they were severely overheated) and only ever had one person complain about the slight squeal and slightly less cold stopping power (but never about brake shudder coming back). One of these cars was my own car (went from auto parts store premium pads to "track day" pads on mine to cure the shudder, didn't change or cut the rotors though)
Stoptech knows their stuff.... I've never had problems with any of their tech advice, only good results.
I will say that Stop Tech has very good insight of the bedding proses. However I will say that their idea of bedding in pads is not practical or even safe for industry auto shops to follow. This doesn't negate that most/ all large industry auto shops do not have a good understanding of what truly causes the "pulsation" their customers are feeling. But is there a more practical way to bed new pads and rotors that doesn't require a private track to do high speed stops that could putting other drives at risk?
55 years doing brake jobs and taking training courses I've never been told much of what is said here. Your information is so detailed and well written I will try these techniques. Thanks!