Scuffing Rotors For New Pads - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 17 Old 09-14-2015, 09:51 AM Thread Starter
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Scuffing Rotors For New Pads

I installed Raybestos ST47 pads on my Cobra this weekend and forgot to scuff up the rear rotors. I scuffed the fronts but forgot to do the rears. I was previously running Hawk HPS pads. After bedding them the rears are now making a humming sound at low speeds as soon as they build up a little heat. They only make the sound when I'm not on the brakes. As soon as I apply pressure the sound goes away.

Should I pull the rears and scuff the rotors up? If so, do I need to do the bedding procedure over again? I mounted my new NT01 tires yesterday and will be installing them this week so scuffing them up then will only take a minute.

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post #2 of 17 Old 09-14-2015, 04:58 PM
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Are you running ST47's on the street?


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post #3 of 17 Old 09-14-2015, 05:58 PM Thread Starter
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I was planning to. I'm going to be running the Roval at California Speedway in Fontana in a couple weeks and I needed new brakes pads. I read that the ST47 are a little noisy but I assumed that just meant that they would squeak a little which is what the front is doing under light pressure coming to a stop. Another thing I've noticed with these pads is that they drag a little. By that I mean that when I'm at a stop light with a slight incline and let off the brake peddle the car doesn't roll like it would before. When I say slight I mean that before the car would roll a foot over about 30 seconds. now it doesn't roll. Could it be that I need to rebuild my calipers?
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post #4 of 17 Old 09-14-2015, 06:00 PM
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Why not have the rotors turned?

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post #5 of 17 Old 09-14-2015, 06:22 PM
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I wouldn't run ST47's on the street. Their cold stopping power will come from rotor wear.
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post #6 of 17 Old 09-14-2015, 06:34 PM
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Yeah, st47s are great track pads... Not for the street, very dusty and noisy, and cold temp friction comes at a price.

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post #7 of 17 Old 09-14-2015, 11:00 PM
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Do NOT turn rotors!!
This is such a misconception in brakes. Every time you turn your rotors, you take off metal and they loose their abilities to cool down and dissipate the heat. So in sense you are taking life off of them. You turn rotors in extreme cases of warping to get them true and at that, I would just prefer to replace them.
To take the glazing off and help with your new pads to seat into the rotors. Just scuff the rotors with sand paper. But if you have air and a air grinder with a Speed-Loc. Put on the green loc pad and place it on one spot on your rotor. Then start turning your rotor by hand. I grab one of the lugs and start cranking. Then you do the same thing on the back side where the caliper is (The caliper is off at this time because you are replacing your pads). When done you will have a very nicely sanded surface that looks like cross hatching in a freshly rebuilt engines cylinder walls. It is something we always called a, "Non Directional Swirl" I have been doing it for 28 years, I did it on NASCAR and dirt race cars I worked on in the early 90s. I did it when I worked in the auto repair industry as a chassis/front end alignment and brakes specialist. and I do it to this day on a customer of mine's landscape work truck fleet that pulls equipment trailers.
This works and it gives you much longer life to your rotors.
I will be happy to take pics of how to do this and post on here soon. I will be doing this to my GT before I go to my first autocross.

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post #8 of 17 Old 09-14-2015, 11:08 PM
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Another thing. Get Permetex Anti Squeak spray. Spray it on the BACKS of your pads. Then reassemble the caliper/pad assembly. This is basically a glue. It keeps the pad stuck to the caliper when off the brakes and keeps them from vibrating. Squeaking or that humming you mentioned is a frequency that is the result of the pad and the rotor just touching and causes the pad to vibrate and let off these frequencies that we hear as squeaking. The spray on the pad keeps the pad stationary on the caliper and deadens the vibrating.

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post #9 of 17 Old 09-15-2015, 08:41 AM
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I keep ST47s on my mach1 which I occasionally drive on the street and drive 5 hours round trip to the track and I've never had any reason to swap pads back and forth. Make sure everything is installed properly and leave it alone. I sure wouldn't spray any of that sticky crap on the back of your pads.

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post #10 of 17 Old 09-15-2015, 09:56 AM Thread Starter
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The hum is not from the pad moving in the caliper it's definitely the from the pad material contacting the rotor and it starts happening after driving the car for a short distance once it builds up a little heat. When the pads are cold it doesn't hum. I drive my car a lot on the street so I'm going to try and get another set of rotors and pads for the street. I already have an extra set of rear rotors and a set of front pads so I just need front rotors and rear pads.

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post #11 of 17 Old 09-16-2015, 07:55 AM
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Quote:
Originally Posted by 94cobra69ss396 View Post
The hum is not from the pad moving in the caliper it's definitely the from the pad material contacting the rotor and it starts happening after driving the car for a short distance once it builds up a little heat. When the pads are cold it doesn't hum. I drive my car a lot on the street so I'm going to try and get another set of rotors and pads for the street. I already have an extra set of rear rotors and a set of front pads so I just need front rotors and rear pads.
As all that stuff goes thru a few heat cycles, especially track use the noises will come and go and change so as long as everything is installed properly don't worry about it.

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post #12 of 17 Old 09-16-2015, 10:00 AM Thread Starter
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Everything is installed correctly so I'm not worried. It's just annoying. I went and ordered some street pads yesterday and will probably be going today to pick up some front rotors so I can install all the stuff I'll be using for daily driving. I won't be running on the track until Oct 4th so I'll swap the track stuff back on Saturday the 3rd. Plus I only live 7 miles north of California Speedway so it's a short drive for me.
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post #13 of 17 Old 10-12-2015, 01:31 PM
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Quote:
Originally Posted by dencon View Post
Do NOT turn rotors!!
This is such a misconception in brakes. Every time you turn your rotors, you take off metal and they loose their abilities to cool down and dissipate the heat. So in sense you are taking life off of them. You turn rotors in extreme cases of warping to get them true and at that, I would just prefer to replace them.
To take the glazing off and help with your new pads to seat into the rotors. Just scuff the rotors with sand paper. But if you have air and a air grinder with a Speed-Loc. Put on the green loc pad and place it on one spot on your rotor. Then start turning your rotor by hand. I grab one of the lugs and start cranking. Then you do the same thing on the back side where the caliper is (The caliper is off at this time because you are replacing your pads). When done you will have a very nicely sanded surface that looks like cross hatching in a freshly rebuilt engines cylinder walls. It is something we always called a, "Non Directional Swirl" I have been doing it for 28 years, I did it on NASCAR and dirt race cars I worked on in the early 90s. I did it when I worked in the auto repair industry as a chassis/front end alignment and brakes specialist. and I do it to this day on a customer of mine's landscape work truck fleet that pulls equipment trailers.
This works and it gives you much longer life to your rotors.
I will be happy to take pics of how to do this and post on here soon. I will be doing this to my GT before I go to my first autocross.
I would be interested in a "how-to"
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post #14 of 17 Old 10-14-2015, 08:39 PM
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I just use a 3M Scotch-Brite disk on my drill, like the bottom ones in this kit - http://www.amazon.com/3M-03050-Scotch-Brite-Automotive-Finishing/dp/B000CPZYCM. I think the ones I have are 3" diameter instead of 2", but whatever. With the rotor off the car I lay it on the ground and spend maybe 30-45sec running the Scotch-Brite pad around each face of the rotor on my drill, then spray it down with brake cleaner and wipe it off. Nothing special.

I do this for both street pads and track pads, works like a charm. The last time I turned a set of rotors was ~15 years ago, prior to my first track event. Since then I've been doing my own pad swaps, and just scuff the rotors myself.

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post #15 of 17 Old 10-15-2015, 08:29 PM
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Quote:
Originally Posted by dencon View Post
Do NOT turn rotors!!
This is such a misconception in brakes. Every time you turn your rotors, you take off metal and they loose their abilities to cool down and dissipate the heat. So in sense you are taking life off of them. You turn rotors in extreme cases of warping to get them true and at that, I would just prefer to replace them.
To take the glazing off and help with your new pads to seat into the rotors. Just scuff the rotors with sand paper. But if you have air and a air grinder with a Speed-Loc. Put on the green loc pad and place it on one spot on your rotor. Then start turning your rotor by hand. I grab one of the lugs and start cranking. Then you do the same thing on the back side where the caliper is (The caliper is off at this time because you are replacing your pads). When done you will have a very nicely sanded surface that looks like cross hatching in a freshly rebuilt engines cylinder walls. It is something we always called a, "Non Directional Swirl" I have been doing it for 28 years, I did it on NASCAR and dirt race cars I worked on in the early 90s. I did it when I worked in the auto repair industry as a chassis/front end alignment and brakes specialist. and I do it to this day on a customer of mine's landscape work truck fleet that pulls equipment trailers.
This works and it gives you much longer life to your rotors.
I will be happy to take pics of how to do this and post on here soon. I will be doing this to my GT before I go to my first autocross.
If you don't have an air grinder take a drill with a circular wire brush. The wire brush needs to have the forward facing bristles [not with the bristles going around the dia].

Take the wire brush in the drill, then cut some 80 grit sand paper just a bit bigger than the dia of the wire brush.

Place the sand paper in between the rotor, and the wire brush. Press the wire brush against the sp, and start the drill. The wires will hold the sand paper in place, but not put too much pressure on them, just enough so that they scuff up the rotor.
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post #16 of 17 Old 10-19-2015, 06:47 PM
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Quote:
Originally Posted by dencon View Post
Do NOT turn rotors!!
This is such a misconception in brakes. Every time you turn your rotors, you take off metal and they loose their abilities to cool down and dissipate the heat. So in sense you are taking life off of them. You turn rotors in extreme cases of warping to get them true and at that, I would just prefer to replace them.
That and when you cut a non-solid (vented) warped rotor you are now creating varying wall thicknesses that will contribute to more warp since the different thicknesses react to heat differently.

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post #17 of 17 Old 10-22-2015, 05:26 PM
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Just so everyone is clear on what a 'warped' rotor really is...

-Warped- Brake Disc and Other Myths
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