Odd caliper damage

[random1781]

Was changing my front brake pads and noticed this small but odd marring on the right side caliper. Racking my brain here trying to imagine how this happened and wondering if anyone has any input. It's only this caliper, and the rotor seems fine. Maybe something got picked up and lodged in there?

 

[Ede-DE]

The damage is where the disk "leaves" the caliper. Damage by an object seems to be impossible. Any damage on the downside of the caliper?

As the caliper is a floating one (as we call it in Germany) I would recommend to check the bushings (Pos. 19) where the caliper is fixed to the frame . Does the caliper sit tight in every position when you pull it out and push it in? What about the 2 bolts (Pos. 21) that hold the frame to the end of the fork?

 

 

Edited January 18 by Ede-DE

[mcbrien]

I agree with Ede-DE. The disc is rubbing on caliper.

[random1781]

7 hours ago, Ede-DE said:

The damage is where the disk "leaves" the caliper. Damage by an object seems to be impossible. Any damage on the downside of the caliper?

As the caliper is a floating one (as we call it in Germany) I would recommend to check the bushings (Pos. 19) where the caliper is fixed to the frame . Does the caliper sit tight in every position when you pull it out and push it in? What about the 2 bolts (Pos. 21) that hold the frame to the end of the fork?

 

 

I agree an object seems unlikely and that the disk itself might be the culprit, but the weird part is that the rest of the caliper (including where the disk "enters" the caliper) is just fine. The bolts (21) are currently and have always been tight.

 

I'll check the bushings as soon as I have some time. When reinstalling the wheel, it seemed like the caliper would slowly slide out of position after pushing on it, but that might have been me knocking it around when putting the wheel back.

[Tenerider]

Although it seems unlikely at first, the damage (especially due to the metal flakes/hones visible) looks like caused by some hard object which has hit and therefore deformed the metal at once - rather not like continuous grinding  (what I'd expect from a rotor touching it).

 

I'd vote for a small stone which got caught in one "wave" of the outer disc, and then being pushed/forced through the caliper.

[Totti]

Where is the damage?

[Ede-DE]

There's an upswept tongue of metal on the caliper that indicates that the disc formed it over more than one rotation and not only an impact of whatever obstacle.

Gents, put your reading glasses on!

[Tenerider]

That's exactly why it does NOT look like continuous grinding over several roations to me.

 

If it has been caused by the rotor, there will be visible marks on the outer (black) rim of the rotor.

[ffasy]

Grinding of the rotor should be visible inside the caliper. Same if there was a stone pushed through.

[dzieburs]

It is worth to check wheel bearings for freeplay. Had same issue at the back when one bearing collapsed.

[Hibobb]

@random1781 I have watched your videos (awesome). With the crap you ride thru, this doesn't surprise me. Lets see a picture of your rotor. My first guess is you have a "wave" style rotor and sand, mud, rocks gets caught and pushed thru the caliper, acting like an abrasive saw. 

[BikeBrother]

I think his dog chewed on it....

Probably a little stone came in between.

[Hollybrook]

I'm with @Hibobb, what does the edge of the rotor look like?  If it's a wave rotor, are there any signs that a small rock for caught in one of the valleys?

[qInvention]

Are both screws that fix the caliper in their place?

[Black99S]

Looks like rough machining swarf - not de-burred.

Or it was thin edge of casting  which was bent back when re-installing the wheel - the disk hit the thin bit and bent it back.

That's my 2Cents worth. 

[random1781]

Yes, the bushings and bolts are fine. If either of those had been loose, I think the marring would have been a lot sloppier. It's very centered along the groove, so I think it's safe to rule those out.

 

It does seem like the rotor would be the cause, because it is centered. However, there is ~5mm between the outer diameter of the rotor and the inner diameter of the caliper where the damage occurred. I think @dzieburs's bearing suggestion is significant, but I've been checking the wheel bearings somewhat obsessively, and they don't have any noticeable problems. They do have ~22k miles on them and are SKF bearings on a Haan hub. The right side spacer (same side as the caliper) does have more wear on it than the left side, which does give me pause, but I think that's unrelated.

 

The outer edge of the rotor is fine with nothing significant on it, and it looks essentially identical to the left rotor.

 

@BikeBrother was really close to figuring it out, but since I have some bones zip tied above the wheel, I think that's where the dog's focus would be.

 

At this point I think it was probably a rock like @Tenerider suggested or my own buffoonery like @Black99S said. Probably the latter.

[mcbrien]

Well hopefully you have now created sufficient clearance so no more issue. Clean off the burrs and keep an eye on it.