Brake rotor issues

[hypophthalmus]

Noticing the front pads were worn, I replaced them.

I noticed a sort of grinding noise, but I figured they might just need to be worn in. I did keep an eye out for grooves in the rotor.

Eventually I noticed a small groove and decided to take it apart again and make sure there weren't any small rocks and such. There didn't seem to be (but I wiped it down anyways), but I did notice two light grooves in one of the brake pads, one in the same location as the groove on the rotor, and one not.

Inspecting the rotor again, I noticed two corresponding points of raised slivers of metal. Using a combination of prying with a screwdriver and *very* light and careful sanding, I got one of them gone (I think), and the other one mostly gone.

I'm wondering what could have caused this, and if I should still be concerned about this.

[Mr. Paul]

Maybe it was a manufacturing defect in the rotor, or a rock strike or something like that. If the pad caused it, I would think the damage would be all the way around the rotor. If it were me, I would keep a close eye on it and be looking for a good deal on a new OEM rotor. Its just too important a part to be worrying about.

[Redk]

I can't imagine what those slivers of metal might be.
Yet, concentric rings on the surface of your disk should not affect your braking ability.
Replace the pads. They will perform very badly until they conform to the somewhat wavey surface and they will be pretty much as good as they ever were.
This is certainly not the Racer's Edge !
If you are flush with extra cash, love your scooter, and mechanics, Purchase a new rotor and top quality pads, assure the rotor is running true with a dial indicator, and proceed with assembly after flushing the hydraulic system properly.
redk

[mrbios]

I've seen that on motorcycles it can be caused by grit or metal from the backing of the brake pads once they wear all the way down.  To test for warp you can remove the rotor and put it on a flat piece of glass.  If you remove the rotor keep in mind loctite often high strength is used on the hex bolts which can strip easily.  The safest thing to do is heat each hex bolt for 30 sec or so with a propane torch to smoke of the loctite, let it cool then use a hex socket and ratchet to unscrew or hand impact tool that you strike with a hammer (available at any auto store for $8).

Finally to remove the record grooves you can use an angle grinder with a 4" cutting disk and touch the side edge of the disk only to lightly scrub off the grooves.  I done it to dirt bikes and atv which get tons of scratches from mud.  Also, on street mototocycles to remove the lip that forms around the inside and outside edge of the rotors.

[hypophthalmus]

I didn't let the pads get too low.  I think the best explanation is that something got between the rotor and the pads, since there was matching grooves in both.

Light sanding the raised bits on the rotor seems to have worked. I haven't felt anything obvious since, and I don't see the spots I sanded. The grooves in the rotor haven't gotten deeper (in fact, one of them I can barely make out, not sure where the other one was). I haven't look at the pads to see how they're doing.

[mrbios]

Sounds like the rotor is in good shape.  I've repaired ones that were much worse.  Also, keep in mind the rear pads wear much quicker as the rear wheel is the drive wheel and gets bent and slightly out of round over time and this causes the pads to drag as the rotor bends to the shape of the wheel same as on most motorcycles.

[CROSSBOLT]

How does the back wheel get bent by being a drive wheel?

Karl

[mrbios]

How does the back wheel get bent by being a drive wheel?

Karl

What I noticed is as the back wheel is rotated the caliper hits in some spots and not others.  The rotor appears straight when I lay it on a piece of glass so I think the back wheel is warped a little bit just like it does on most motorcycles.

This also causes the rear rotor to always be warm even if it's not used well the front rotors will usually be cool.

[Ernst]

Thanks for the topic.

 I am replacing my two front rotors and all pads.
I will look at rear rotor closely now.