Garnet Sanding for Rotors

[thescreensavers]

I got some shudder and simply sanding with Garnet paper should solve it if its just pad material

If only a small amount of material has been transferred i.e. if the vibration is just starting, vigorous scrubbing with garnet paper may remove the deposit. As many deposits are not visible, scrub the entire friction surfaces thoroughly. Do not use regular sand paper or emery cloth as the aluminum oxide abrasive material will permeate the cast iron surface and make the condition worse. Do not bead blast or sand blast the discs for the same reason.

Now for instance, http://www.harborfreight.com/7-pack-100-grit-garnet-sanding-sheets-92742.html

If you look into the specifications it says "Material Aluminum Oxide"


So uh what the heck?

 

[skyking]

typically, pulsations or shudder is due to warped rotors. I don't bother turning rotors any more, because once they get heated up good enough to warp they will do it again soon after turning them. They are cheap enough to replace.

 

[thescreensavers]

^ The last time this happened was 17k miles ago, thats when I turned the rotors. So I believe that its just pad material.

 

[lghost]

I am needing to find some garnet paper as well, that or keep turning/replacing rotors every 10k on my POS Celica. Just recently did it again and sprang for new EBC pads, complete fluid flush and replace, still happening.

grumble, grumble, grumble

 

[Bartman39]

typically, pulsations or shudder is due to warped rotors. I don't bother turning rotors any more, because once they get heated up good enough to warp they will do it again soon after turning them. They are cheap enough to replace.

This...:thumbsup: (garnet paper is an OLD gimick not a solution the pulsation will return soon if it ever leaves)

Also warped rotors that have been turned are most of the time a very close to the min spec which is set for more than one reason... Min thickness means they are much more likely to warp or possibly fail... Also driving habits affect how fast or if they warp as well, in addition when turned it matters how they are broken in with new pads as well (very critical)... Hard fast stops and or stop and go driving in town tend to heat up brakes and combined with possibly wet driving conditions and as mentioned min thickness on the rotors can result in a pulsating condition or warped rotors... Remember most rotors are made from cast iron and when heated and cooled to rapid they will warp and should just be replaced... Most cars have very thin rotors to start with as well and they are not designed for heavy duty braking as with trucks which have larger brakes because they are rated for towing... High performance cars do have better braking systems but your average cruiser has the min required and for sure small light compact cars...

From doing brakes for 30+ years I would suggest Wagner rotors and Wagner Thermoquiet pads... Had one and only 1 bad rotor out of the box and 0 pad issues... Other brands of rotors I have had to turn on the lathe new out of the box after installing and finding out they were machined by someone that could not speak english in another country...? Pads come down to the material and how it was prepped... Thermoquiet pads have an excellent compound and are baked in a certain process...

 

[thescreensavers]

^ Ace Hardware should sell them too but the one nearby did not have 120, I just bought it on amazon since I am not sure about the harbor freight ones.

 

[JCH13]

I am needing to find some garnet paper as well, that or keep turning/replacing rotors every 10k on my POS Celica. Just recently did it again and sprang for new EBC pads, complete fluid flush and replace, still happening.

grumble, grumble, grumble

If you're warping rotors every 10k miles you need to reevaluate your rotor purchases, your driving habits, or both. Premium rotors might cost 2x as much, but if they last 4x longer... well, the math is left as an exercise to the reader.

 

[Apex]

I got some shudder and simply sanding with Garnet paper should solve it if its just pad material


Now for instance, http://www.harborfreight.com/7-pack-100-grit-garnet-sanding-sheets-92742.html

If you look into the specifications it says "Material Aluminum Oxide"


So uh what the heck?

Sanding is a smart thing to try first, since pulsation or shudder is almost never rotor warping.

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

Myth # 1 – BRAKE JUDDER AND VIBRATION IS CAUSED BY DISCS THAT HAVE BEEN WARPED FROM EXESSIVE HEAT.

The term "warped brake disc" has been in common use in motor racing for decades. When a driver reports a vibration under hard braking, inexperienced crews, after checking for (and not finding) cracks often attribute the vibration to "warped discs". They then measure the disc thickness in various places, find significant variation and the diagnosis is cast in stone.

When disc brakes for high performance cars arrived on the scene we began to hear of "warped brake discs" on road going cars, with the same analyses and diagnoses. Typically, the discs are resurfaced to cure the problem and, equally typically, after a relatively short time the roughness or vibration comes back. Brake roughness has caused a significant number of cars to be bought back by their manufacturers under the "lemon laws". This has been going on for decades now - and, like most things that we have cast in stone, the diagnoses are wrong.

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. I have seen lots of cracked discs, (FIGURE 1) discs that had turned into shallow cones at operating temperature because they were mounted rigidly to their attachment bells or top hats, (FIGURE 2) a few where the friction surface had collapsed in the area between straight radial interior vanes, (FIGURE 3) and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not. (FIGURE 4)

In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures.

 

[thescreensavers]

^ Yep, the quote in the OP is from stoptechs website.

 

[exdeath]

It's only a warped rotor if the steering wheel has a vibe/wobble to it when you are not on the brakes. If it's a pulse only when you apply the brakes, it's uneven pad material on the disk or crystallized/alloyed hard spots in the rotor from overheating.

Turning or sanding a rotor with hard spots and heat damage will only fix it for a few miles. The hard spots are throughout the permanently chemically altered metal and as the rotor wears, the hard spots stay behind to cause high areas to resurface as the softer material wears, causing uneven surface again.

Also a proper brake job involves indexing the rotor in every possible position on the hub, measuring runout with a dial indicator, and using shims to make sure the rotor turns true with the hub. But few people and places actually do that, they just turn the rotor and throw it back on the car. I'll admit I just threw new rotors on the Camry and didn't do it either even though Toyota has 5+ pages in the service manual with the step by step procedure.

Most places won't even mark the position of the rotor to put it back on the hub the same way like they are supposed to, which can introduce new vibrations that weren't there before if they were indexed by the factory. The straightest newest rotor in the world won't fix anything if it's slightly skewed on the hub more than .005" or so. Things like that and getting perfect braking is the difference between taking your car to Jiffy Lube for brakes or the Mercedes dealership.

 

[Viperoni]

Sanding is a smart thing to try first, since pulsation or shudder is almost never rotor warping.

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

All of this is true.


Get better brake pads.

I race my car, on slicks, and just make sure to properly do a cool down lap along with using the brakes as little as possible (including not pulling the ebrake after parking), never have a problem.
I've run EBC redstuff and yellowstuff pads.