[jeffscott]

So, I just mounted up my new XTR brakes, front is fine, but the rear is not.

I thought my rotor might be shot and sure enough it is. There is a very noticable ledge between the running surface and the support, and it is getting bigger quickly.

I will change the rotor and see.

My question is, why, this occurred very quickly, and only on one rotor surface (outboard rear), are the rotors surfaced hardened so once you wear through the wear rate increases quickly??

 

[crisillo]

Umm.. that sounds weird... over how much time did this wear take place?

The ledge itself is normal wear...but it shouldn't appear very fast...

 

[jeffscott]

I was beginning to think I had the problem Jan 5, changed brakes, Jan 7, for sure had it jan 18, really bad yseterday. Only 300 km of riding.

 

[crisillo]

Wow... that was very fast... lots of downhill in those 300kms???

also.. organic or metal pads????

Metal/sintered pads wear the rotor less from what I gather and last longer....

 

[jeffscott]

I have the Shimano metal pads on, the pad that is on the ourter rear is seeing wear others are good.

No not alot of braking, no more than normal.

 

[energetix]

I'd be checking wether one pad/piston is engaging at a different rate than the other. Sounds like that particular pad/piston must be putting more force on the rotor than the other if that's even possible?
Or could it be a pad manufacturing anomaly where the pad material is harder than normal?
I guess the best way to isolate the problem somewhat is put another rotor on & see if it happens again - if it doesn't then chances are that it's not the rotor.

 

[jeffscott]

yup, i'll chang'm tonight.

so no hard surfacing of th rotors?

 

[crisillo]

yup, i'll chang'm tonight.

so no hard surfacing of th rotors?

I don't think so... I mean the surface is meant to scraped in order to brake... (no actual knowledge, just a guess)

 

[ferday]

for the record, there is NO coating of any kind on a brake rotor (at least a regular steel one)

that's serious wear jeffscott, i've had rotors for years (and thousands of km) that see heavy DH use (and you know our area) and they are still fine...

 

[jeffscott]

Yes I understand that there is not a coating on the surface, I was referring to maybe a flame hardening of the rotor surface itself.

Yes the wear is very quick, I will tear apart tonight.

 

[jeffscott]

So I tore it down.

The rotor was .0625 inchs thick at the edge, thin in the middle the new on was 0.0670 inches thick so really worn.

The outer pad the worn side was also jsut about completly worn out, spring not quite dragging, inner pad not worn at all. See pictures.

Squeezed lever and the inner piston moved (the pad with no wear) outer (pad with wear) seemed locked.

Then inner piston kinda come out, so I pushed it back in.

Bled the brakes (lot of air came out), both pistons seemed to be moving and remounted everything with new resin pads and a new rotor.

Lever seemed a little stiffer, brake seemed better.

I will try it out, but still don't get it.

 

[crisillo]

So I tore it down.

The rotor was .0625 inchs thick at the edge, thin in the middle the new on was 0.0670 inches thick so really worn.

The outer pad the worn side was also jsut about completly worn out, spring not quite dragging, inner pad not worn at all. See pictures.

Squeezed lever and the inner piston moved (the pad with no wear) outer (pad with wear) seemed locked.

Then inner piston kinda come out, so I pushed it back in.

Bled the brakes (lot of air came out), both pistons seemed to be moving and remounted everything with new resin pads and a new rotor.

Lever seemed a little stiffer, brake seemed better.

I will try it out, but still don't get it.

I hope that solves it...maybe it's the pic, but the pad doesn't seem completely worn out... however because of the uneven wear I would go with new pads, just to make sure... keep an eye on them because organic pads won't last as long as metal ones (especially when wet)

Keep us posted..

 

[jeffscott]

The brake bedded in well this morning and seems to be working much better.

So I guess I'll just ride it, still can't figure out what happened.

Yeah, there is less on the other end of the pad, so maybe some sort of alignment problem.
It just seems weird cause I never noticed any brake drag at all.

 

[XSL_WiLL]

Well, if you have air in the system, it will inhibit movement of the pistons, if the caliper isn't centered, you could also get that problem. And by the looks of it, one piston was dragging. This would cause the accelerated wear. And of course it'll result in a spongey feel and poor performance. I'm surprised you didn't notice significant fade.

 

[jeffscott]

The air in the system might explain it hanging up one piston. But I would have thought that the lever would have felt quite spongy, (just a little bit more than the front). I figured I got the air in one the one piston kinda popped out during the tear down.

The weird thing is the hung up piston outboard, had the worn out pad, wouldn't it be the other way around??

If it was dragging, I am going to be going about 50 km/h, cause I was doing my average times on my commute.

Yeah, by the last week sqeaking and fade were there.

 

[jeffscott]

I think i got it.

The same squeak came back and the alingment was a bit off.

So I set it up again, this time I found the rear der hanger bolt was loose!!!

Tightened it up and re-aligned and I think I got it..

The hub had worn out, and wiggled I think this might have loosened the bolt up, I fix the hub, and put the brake on at the same time, but missed the rear der bolt.

 

[crisillo]

I think i got it.

The same squeak came back and the alingment was a bit off.

So I set it up again, this time I found the rear der hanger bolt was loose!!!

Tightened it up and re-aligned and I think I got it..

The hub had worn out, and wiggled I think this might have loosened the bolt up, I fix the hub, and put the brake on at the same time, but missed the rear der bolt.

Sounds like you got it.... the alignment must have definitely been quite a bit off...

Hope that's the end of it...