Intro: Prepping Used Rotors for New Pads
Now if the title of this isn't clear enough I don't know how much more I can help you =)
This technique can not only be used for new pads, but also to try to diagnose other problems you might be having with your current rotors.
On my motorcycle I have a slight warp in the left side rotor so it's not quite useable so I decided to go ahead and buy some used oversized rotors since I'm going to be there anyways. This technique can be applied to all rotors and I highly recommend it!!
After checking to make sure that your rotors are straight (I mounted mine in a lathe and used a runout gauge to check for both concentricity [how circular they are] and also to make sure that there was no warpage on the disk itself) go ahead and give them a good cleaning.
Now I do have two methods available to me, one of which can be done at the techshop and the other is more specailized so I'll be covering the one that most people will have access to which is going to be a standard drill cleaning method.
-Drill or Mill with circular vice (YAY TECHSHOP!!!)
-quiklok carrier (or similar)
-*Medium Grade metal surface prep disks (non-silicate and non abrasive)
*welding prep disks work very well, they leave no residue and they do not marr the rotors at all under normal useage. Fine grade will work as well and leave you with a slightly better surface finish but it will take quite a while to do so as it is very slow to remove the material.
Step 1: Initial Clean
Firstly I'd suggest taking the rotors off of the wheel to prevent a large amount of particulate from ending up in critical bearings (ask me how I know how much it sucks to blow a bearing while riding).
You can put painters tape over the orfices but I decided to just go ahead and unmount them completley from the rim.
Now that you're staring at your rotors you should notice some slight discoloration (brownish, grey) all over the rotors. This is what we're trying to remove.
As you can see in the picture below, In my case I have some really light surface rust from being next to steel parts (the rotors themselves are stainless steel) and just general dirt, and some brake pad reside (not good for new pads).
The first step in cleaning is a general degreasing using simple green or a similar environmentally friendly product to get off the major grease and grime. If you leave it on there it will be fine but you will load up your scouring pads very quickly and it will end up costing you quite a bit more in time, labor and more pads.
Step 2: Using Your Drill
Second mount up your cleaning pads to your drill. They all have various operating speeds so make sure to check before you run the pad at 1500000000 rpm.
My particular set was from Norton and max speed was 4k, I probably was spinning it at 1300 on a standard corded drill with a standard locking chuck.
Try to get the pad as perpendictular to the drill chuck as possible, having a wobble in the head will make things a little bit more difficult.
Now that you've got your tooling set up its time to actually start working on the rotor.
Placement of the rotor is important as if you have floating rotors like most modern bikes do, you can risk bending the carrier by applying too much pressure. I used a styrofoam sheet that I had laying around and carved out a general profile for the rotor so when I applied pressure down it wasn't on the carrier.
This can be done safely if you use light pressure on the center of the carrier with a soft object like a cloth around your fist.
Using a light pressure on the drill and keeping it at a right angle to the rotor surface, you can start working your way around the rotor.
I found that moving the drill in small circles, moving counterclockwise around the rotor produced both the best surface finish and cleaned the fastest; if you see heavy "swirls" in the metal, you're likely applying too much pressure or you have something embedded in the pad that is making the swirls.
I was able to get an entire rotor (both sides&the carrier) cleaned up with one pad and there was no scoring on the metal.
When you're finished the metal should be a uniform shine and should feel very clean to the touch rather than gummy and sticky.
If you don't know what I'm talking about run your fingers across a rotor that has been cleaned, and one that hasn't!
Step 3: A Final Check of Your Work...
I found that even after I examined them quite closely in good light there were still a few "dark spots" on the rotors that indicated left over pad material that was a little more resiliant.
I went ahead and took a sharpie and looked at the reflection of a constant light on the rotor and marked all the spots that were dark and went in again and cleaned them up. quick and efficient and its the little steps that make the biggest difference in something as critical as your brakes!
Step 4: Installation!
Before installing the rotors insure that they are clean by giving them a quick rinse in brake cleaner, unfortunatley the aersol cans are the best for this so use minimal amounts to clear off any debris and left over oils that may have accumulated on the rotor in handling and cleaning.
Always wear gloves while installing rotors to ensure that no oils from your hands or the vehicle get on the rotors! No pictures of them on the bike yet but I will update them asap!
Cheers and happy wrenching!
I did this at the techshop San Jose! SO CAN YOU!