Rear rotor failure - ever seen this?

[Piernas Flacas]

Now you have 2 interesting cookie cutters!

[Steven Knoetze (sk27)]

Definitely rubbing over a prolonged period of time that. Surprised it wasn't heard while riding.

As mentioned, would love to see pics of the inside of the caliper or brake caliper mounts.

[M L]

21 hours ago, CLC5850 said:

Hi there. I had this happen to me and in our group with many kilometers done no one had. The guy who supplied to me said he sees it all the time! I was rather surprised and I wasn't down to steel on steel with my brake pads. So I am interested to know if others have seen it. Cheers

Not sure what happened there but I'm pretty sure e-bikes are to blame.

[M L]

6 hours ago, TheoG said:

Too many idiots out there that THINK they know what they doing ....  

Too many bike shops hiring "mechanics" at R350 a day and then expect knowledge and expertise.

[TheoG]

Just now, M L said:

Too many bike shops hiring "mechanics" at R350 a day and then expect knowledge and expertise.

Yip, if you pay peanuts you get monkeys ... 🤪

[David Marshall]

That brand of disc is as good as any of the other cheap brands.  They work well but don't last as long as some of the more expensive ones.

The failure point on that disc is below the normal braking surface so as mentioned it's more likely to be a fitment issue that the material one.

I have seen a disc shear in the middle of the braking surface before and have a collection of "near misses" that I keep for illustrative purposes.  

Use a caliper rather than a vernier to measure rotor thickness as the wear tends to be uneven and measure in a number of places.

[FirstV8]

I concur with the mention of the caliper being put back without the spacers for the correct size rotor . Another reason a rotor can be sheared off is if you have a seized piston on one side and the rotor is being pushed out of alignment against the seized one on the opposite side . I personally had  that on a front brake caliper . I remedied it as soon as got home . When braking i would notice the rotor being pushed over and the braking was not as normal with the lever also being a bit squishy/soft or in F 1 terms a long brake pedal .  

[PhilipV]

5 hours ago, dave303e said:

the caliper spacer/washers/universal join spacing is incorrect on the bike. The caliper is sitting probably 3-4mm too close to the center of the axle(point of rotation). Your break pads should only contact with the outer circular part of the rotor and not the break rotor "spokes" for lack of a better word. My 2c is that someone removed the caliper at some stage and didn't put washers/spacers back in correctly...

I concur with this assessment. 

[capediver]

Rotor upsized, caliper mount not....amateur hour....lucky escape

Edited September 22, 2022 by capediver

[NotSoBigBen]

I don't have the experience many here do but I have seen strange wear like that, not broken off though, when a 205mm rotor was used in a 200mm caliper setup.

I was still surprised that the rider didn't notice any strange sounds, scraping of the outer edge of rotor against the metal of the caliper or the pads touching on the little parts of the rotor.

I put 5mm spacers in and solved it that way ..  he's still riding it like that now

[Paul Ruinaard]

11 hours ago, capediver said:

Rotor upsized, caliper mount not....amateur hour....lucky escape

Thats what i said as well.

[Weimaraner1]

Can the OP tell us the thickness of the rotor. The have a 1.5mm wear limit generally and it is good practice to measure wear with a micrometer from time to time and replace if close to or outside the limit. Does look like the pads ran low.

[MORNE]

Im not gonna say which shop, but i got me a 203 rotor for the front this week. Fork is 180 postmount stock.  The only caliper adapters they had was the normal shimano SM90 180P/P2, the one everyone uses to upgrade to a 180 rotor up front on xc forks. That would have been fine if i had a 200mm rotor. I have like 6 of those adapters in my spares box.  I was told that the “1.5mm difference does not really matter”. I went to another shop to go find a 180-203 one instead😅….

Edited September 24, 2022 by MORNE

[BaGearA]

1 hour ago, MORNE said:

Im not gonna say which shop, but i got me a 203 rotor for the front this week. Fork is 180 postmount stock.  The only caliper adapters they had was the normal shimano SM90 180P/P2, the one everyone uses to upgrade to a 180 rotor up front on xc forks. That would have been fine if i had a 200mm rotor. I have like 6 of those adapters in my spares box.  I was told that the “1.5mm difference does not really matter”. I went to another shop to go find a 180-203 one instead😅….

the 203 ones are very hard to get hold of tbh 

 

most of the time I use A washer under the top bolt of the adaptor and Bob's your uncle, been doing so on my bike for years and clients that know about it always say yes and haven't had issues.

 

bigger issue is getting hold of the 180/203 adapter for the few that won't go otherwise 

[MORNE]

9 minutes ago, BaGearA said:

the 203 ones are very hard to get hold of tbh 

 

most of the time I use A washer under the top bolt of the adaptor and Bob's your uncle, been doing so on my bike for years and clients that know about it always say yes and haven't had issues.

 

bigger issue is getting hold of the 180/203 adapter for the few that won't go otherwise 

Evo bikes had them in store so i was sorted on the first try. Yes im one of those people 😊. i just need a IS 160-180mm rear now…those are even more rare. My mild pseudo OCD cant handle the 2 adapters stacked on each other. (IS 160 + 180P/P2 for the 180mm rear) 

[BaGearA]

13 minutes ago, MORNE said:

Evo bikes had them in store so i was sorted on the first try. Yes im one of those people 😊. i just need a IS 160-180mm rear now…those are even more rare. My mild pseudo OCD cant handle the 2 adapters stacked on each other. (IS 160 + 180P/P2 for the 180mm rear) 

lol struggled with one of those for A Santa cruz a few years ago 

 

I still prefer IS if im being totally honest