Rear brake rotor question.

[pablo]

I bought new brake pads for the rear brake because it looks like they were starting to get thin. When I rubbed my finger over the rotor, it is dished out in two places on both sides of the disc. It's like there are two circles of wear opposite each other. I did not put the new pads on thinking I may have to replace the rotor. The brake still works great; good lever pressure, no squealing, and the brake pads still have some thickness, but the disc is not smooth like on the front rotors. What do y'all think? Is this normal? What would cause the disc to wear like this? Should I leave it or replace it???

[ells]

I'd take the pads to near the minimum then replace both the pads and rotor, unless the rotor can be turned, but not sure if it can be.

[dkdixie]

Originally Posted by Ells

I'd take the pads to near the minimum then replace both the pads and rotor, unless the rotor can be turned, but not sure if that can be.

Rotors to thin to be turned.

[dogdoc]

+1 with Ells,

[Cajunrider]

Pablo, Is this the first time the rear pads are replaced? They quit using asbestos in brake pads years ago and started impregnating the newer pads with metal to make them last longer. Nothing is as good as asbestos on brake pads, piping insulation, or linoleum floors. I've been to many asbestos seminars because we have so much of it in our plant used as hot piping insulation and building siding and roofing. As long as the fibers are not friable (blown or made to fly) it is the most durable and best material in the world. So many older mechanics having been diagnosed with asbestosis forced the government to pass new regulations phasing it out. Rotors take a real beating with those metal impregnated pads.

[pablo]

Yes, this is the first time to replace pads. I already have the brake pads; they are supposed to be OEM for the rear brake. If the pads are causing the rotor wear, then the new one's will probably eat up the new rotor and I'll end up in the same situation (although I haven't heard of others with this problem). If I just replace the pads, wouldn't they conform to the shape of the disc?

[Cajunrider]

I read your first post again and if the worn spots are uniform and directly across from eachother it doesn't sound like what I mentioned earlier. I'm going to check my rear rotor to see if it's doing the same. You might want to mic the thickness of the rotor at the worn spots and check to see if it is still above the service limit of 0.24". I doubt the pads have worn down to the rivets. It seems like if they have you would have felt it when applying the rear brake. The service limit on the pads is 0.04". All specs come from the service manual.

[rewindgy]

Not sure why but both my 99 Drifter 800 and my 06 Nomad eat rear brake pads!
Used to get 2 - 3 times the Km on my Ventures pulling trailer and 2 up! Since both of these bikes do not have linked brakes I use the fronts mostly! On the Ventures they were linked so you tended to use both front and rear together! Just an observation!

[macmac]

I don't understand... Is this a spot say 3 inches by 3 inches where there is a depression? if so I find that very odd.

If it is a depression showing general wear all the way around the rotor, but more central to the entire circle that could be normal.

New pads on a old rotor in time will wear in to the shape of the rotor, but you won't have max braking till that happens.

One cause might be if you live in a place that has flint chips in the road, which is turned to dusts... or maybe a place where silica is, in quartz and other hard stone that becomes dust.

[blowndodge]

you guys know that rotors are not supposed to be perfectly smooth and flat right? there has to be some uneven spots to push the pads away when you release the brake. Built in wobble zones if you will....

[pablo]

They are all the way around the rotor on both sides. It is a slight depression; one nearer the outer edge and one a little further toward the center of the disc. If you take your finger and thumb and touch both sides of the rotor toward the center and move your fingers toward the outer edge, you can feel two slightly dished out areas on each side.

[dogdoc]

from what you describe Pablo, it sounds like the outer edge and inner edge of the disc pads are digging in too deep if you will. not sure why yours is doing this and others are not. Do you use mainly your rear brake for most of your stopping power? I've seen cars/trucks just have groves starting to dig into the rotors from various reasons. Im sure it could happen to bikes too.

[pagemastr]

Originally Posted by Blowndodge "Darksider"

you guys know that rotors are not supposed to be perfectly smooth and flat right? there has to be some uneven spots to push the pads away when you release the brake. Built in wobble zones if you will....

I have to disagree with you BD. Using GM specs as an example, lateral runout of .003" is the service limit, as is .001" variation in thickness measured around the rotor. I have been involved with aircraft brake rotors and those are surface ground flat and true both sides. The whole idea of turning any rotor is to get the surfaces flat and parallel with no runout.

I do agree the rotors are too thin to be machined on most motorcycles, a non-serviceable part.

Pablo: Replace the pads so long as the brakes are not pulsing during a stop and do not exceed the service limits mentioned above, you'll be fine.

[pablo]

After looking at all the comments and suggestions, I think I'll replace the pads and see how it feels. I do not use the rear brakes excessively. Mostly I use both front and rear and have never locked up the rear wheel since getting the car tire. I think I locked it up a couple of times on the motorcycle tires. Anyway, thanks for all the feedback.
Pablo

[cactusjack]

[quote=Jack C.]

Originally Posted by "Blowndodge "Darksider"":kzfzyb9q

you guys know that rotors are not supposed to be perfectly smooth and flat right? there has to be some uneven spots to push the pads away when you release the brake. Built in wobble zones if you will....

I have to disagree with you BD. Using GM specs as an example, lateral runout of .003" is the service limit, as is .001" variation in thickness measured around the rotor. I have been involved with aircraft brake rotors and those are surface ground flat and true both sides. The whole idea of turning any rotor is to get the surfaces flat and parallel with no runout.

I do agree the rotors are too thin to be machined on most motorcycles, a non-serviceable part.

Pablo: Replace the pads so long as the brakes are not pulsing during a stop and do not exceed the service limits mentioned above, you'll be fine.[/quote:kzfzyb9q]

I used to do automotive brakes for a living. You are correct, Jack. Rotors are trued on a lathe, there should be virtually no runout.