[DoctorJD]

Back story: I'm a long-time XT brake fan. I've used them on my last two builds and I've had zero issues with them, I love the feel and the stopping power. I bought a 18' Carbon Comp last year and it came with Sram Level brakes on it. Not a fan. Switched out the rear with XT (haven't changed the front yet). Thus far, it has been an exercise in frustration:

The bleed didn't go as smoothly as past XT bleeds I have done. I've had to do a few "mini bleeds" to get them as firm as they should be. Mission accomplished. However, the grip between the pads and the disc leave A LOT to be desired. You can't lock up the rear if your life depended on it (not that I go around locking up the rear, just an illustration of how weak they are). Oh, and they are howling, something I've never had an issue with XTs.

I'm not sure what kind of pads the Srams came with, but I'm using metallic pads. I didn't clean the rotors when I did the original install. I thought that was the culprit, but I have since put in brand new pads, and I've resurfaced the rotor with emory cloth, and cleaned it with alcohol. Still, no bueno.

Here are some suspects:

I'm not using the Shimano brake bracket. The Camber has two bushings on the rear brake mounting posts where the Shimano bracket/adapter would be. I didn't see the need in installing it, I figure the bushings serve the same purpose.

After all of my "mini bleeds" the pads are really close to the pads. Not rubbing, mind you, but really close, like 1mm.

Despite my efforts to clean those rotors, maybe I didn't get them thoroughly clean. With new pads, and a sanded rotor, you'd think you could rule those things out, but I guess not.

What say you, mtbr nation? Any ideas which way to turn? Thanks!

 

[eshew]

It does sound like contamination is the issue. Discs, even from a different manufacturer shouldn't be behaving that way.

My go to solution is to clean the rotors with rubbing alcohol & remove the pads ( I always use metallic) and torch them with a propane torch for a minute. I'll repeat the heating cycle if I can see a large amount of smoke or boiling liquid. Let them cool & gently sand & reinstall.

I've brought back many sets of pads this way, all were behaving like yours, howling with no grip, obvious signs of contamination.

 

[202cycle]

Remove the pads and check the back plate for a tiny ring of fluid. I've seen many Shimano brakes that leak just a tiny bit through the piston seals. It's just enough to contaminate the pads, and only takes a minute of riding to do so. Shimano has always replaced them.

I'm not saying this IS the problem, but it sure is easy to check and may save your hairline.

 

[Aglo]

Did you try to realign the caliper? Bad brake performance and howling are symptoms that could indicate bad alignment.
Even if they look like they are align, a minor deviation is all that's need to have bad brake performance.

 

[DoctorJD]

Thanks guys. eshew, I'll torch those pads and see if I can bring them back to life.

202cycle, I actually suspected an oil leak from the start. Since I had a bit of trouble with the initial bleed, I thought that maybe I didn't tighten-down the bleed bolt good enough and it was sucking air/leaking fluid. It was fine, but I never considered that I could have a piston seal leaking. I don't recall any trace of oil on the backing plates, but I'll give it another look.

Thanks for chiming in, guys!

 

[DoctorJD]

Actually I haven't, other than the eye test. I'll check that out tonight, as well.

PS That was intended for Aglo.

 

[eshew]

Good luck! Let us know how it turns out.

 

[PuddleDuck]

This article is the best I've seen regarding cleaning rotors and pads.

Enduro Mag - Enduro Workshop: Fixing noisy disc brakes

It sounds like it's more complicated than cleaning though.

 

[DoctorJD]

This article is the best I've seen regarding cleaning rotors and pads.

Enduro Mag - Enduro Workshop: Fixing noisy disc brakes

It sounds like it's more complicated than cleaning though.

Thanks PuddleDuck, I'm about to go through that whole procedure (again) except this time, I'm burning the pads.

I checked alignment last night, and it was off a little, so I readjusted and it's still squealing. I was also able to rule out oil contamination. The pads (specifically the back plates) were oil-free. Nothing in the caliper body, either.

The pads looked suspect, however. They were extremely glazed-over, I dare say, "glossy". And black, really black.

 

[Aglo]

If you are dragging your brakes until they glaze it's normal for them to be covered in black dust.
If you are not dragging them, I can't think of anything that would make them turn black, maybe some residue from you brake cleaner if you are using some.
Don't forget to properly bed in your pads, don't get inpatient and cut short the process.

 

[PuddleDuck]

Thanks PuddleDuck, I'm about to go through that whole procedure (again) except this time, I'm burning the pads.

I checked alignment last night, and it was off a little, so I readjusted and it's still squealing. I was also able to rule out oil contamination. The pads (specifically the back plates) were oil-free. Nothing in the caliper body, either.

The pads looked suspect, however. They were extremely glazed-over, I dare say, "glossy". And black, really black.

re-reading your original post, if you can't lock the rear wheel you probably still have air in the system.

"Glossy" pads definitely sound like an issue, and would explain noise issues

Given that you have both power issues and noise issues, I'd
- bleed the brakes,
- sand the pads,
- sand the rotors,
- then bed in the pads/rotors (you must do this. I've read that Shimano brakes are less sensitive to this than others, but maybe not if you're using a SRAM rotor)

Also regarding the noise:
There may be some issue with the mounting, and even that you're not using a Shimano rotor (even though in theory that shouldn't matter)

 

[DoctorJD]

re-reading your original post, if you can't lock the rear wheel you probably still have air in the system.

"Glossy" pads definitely sound like an issue, and would explain noise issues

Given that you have both power issues and noise issues, I'd
- bleed the brakes,
- sand the pads,
- sand the rotors,
- then bed in the pads/rotors (you must do this. I've read that Shimano brakes are less sensitive to this than others, but maybe not if you're using a SRAM rotor)

Also regarding the noise:
There may be some issue with the mounting, and even that you're not using a Shimano rotor (even though in theory that shouldn't matter)

Update:
As I said earlier, I pulled the pads and the rotor back off. I resurfaced the rotor again (with 150g emory cloth). I sanded the pads back down and hit them with a torch after a washing in alcohol. I re-sanded them and cleaned them--again--in alcohol. Reinstalled everything and did about 10 runs to bed them in and then it got dark. I wasn't feeling the brakes getting any stronger. I'm going to finish bedding them in this afternoon and then hit the trails.

As you said Puddle, in my experience, Shimano brakes aren't really that sensitive when it comes to the bed-in process. I've typically done a half-dozen runs, and hit the trails with no adverse effects.

I keep coming back to two things:

Although I'm getting good modulation, perhaps this is misleading me into thinking that I'm getting the proper torque out of the system. If I get out there today and the problem persists, then I'll do another full bleed.

If that doesn't work, I'm changing out the rotors with Shimano and replacing the pads. I've never heard of a rotor being contaminated to the point that you couldn't bring it back, but damn, I don't know what else it could be.

Again, thanks for your input guys!!

 

[MSU Alum]

I've used XT brakes on 6 bikes. I've never had a problem caused by contamination on any of them that couldn't be remedied by wiping the pads and rotors down with alcohol on a rag. The one time I had a persistent problem was on a brake that was brand new and it turned out to be a faulty brake. I got it replaced on warranty and the problem was solved.

 

[eshew]

Darn that is frustrating... If you're getting new pads anyway pull off the old ones again and torch em for 2 minutes each pad. Don't worry about sanding or alcohol. Just burn the heck out of the brake material toss em back on and see if that makes any difference.

Should be enough to burn any deep saturated contamination and put the pad material in a like new state.

 

[fredcook]

DoctorJD, I had purchased a bike that came with SRAM brakes, and immediately wanted to get back to XT brakes. I swapped the calipers from another bike I have, but being impatient, I didn't wait for the Shimano rotors, and went with the SRAM rotors the bike came with. I used new Shimano pads (metallic), and decontaminated the SRAM disks. My results were similar to yours. Long story short, I put Shimano's RT86 rotors on the bike, didn't replace or clean the pads, and everything is perfect. I agree that mixing caliper/pad brand with rotor brand shouldn't matter, but I can't argue with my results.

 

[DoctorJD]

DoctorJD, I had purchased a bike that came with SRAM brakes, and immediately wanted to get back to XT brakes. I swapped the calipers from another bike I have, but being impatient, I didn't wait for the Shimano rotors, and went with the SRAM rotors the bike came with. I used new Shimano pads (metallic), and decontaminated the SRAM disks. My results were similar to yours. Long story short, I put Shimano's RT86 rotors on the bike, didn't replace or clean the pads, and everything is perfect. I agree that mixing caliper/pad brand with rotor brand shouldn't matter, but I can't argue with my results.

I just ordered new rotors this morning. Should be here on Friday. Like you said, it shouldn't matter, but I'm covering all the bases.

 

[DoctorJD]

Darn that is frustrating... If you're getting new pads anyway pull off the old ones again and torch em for 2 minutes each pad. Don't worry about sanding or alcohol. Just burn the heck out of the brake material toss em back on and see if that makes any difference.

Should be enough to burn any deep saturated contamination and put the pad material in a like new state.

Thanks, I didn't torch them near that long. I've got a new(ish) set that are on my workbench as we speak. I'll use that method on them.

 

[DoctorJD]

Update:
So yesterday, I was going to get down to the bottom of this. With the setup as described in my original post, I re-bled the system just to eliminate that as a suspect. After the bleed, I took it out and no change in performance, and it was still screaming like a banshee.

So I mounted a new Shimano brake rotor. I also took the original metallic pads (that came with the XT brakes) and gave them the once-over (burned, cleaned). They were shining like a new penny. Went out for a test run and the howling was gone. The braking power on just one run was the same as I was getting from the previous setup after weeks of riding.

I wasn't able to get a full bed-in done (only did about six runs) but I can feel the grip coming back. Not full power, mind you, but better.

So the rotor was the difference. I can only theorize that the Sram rotor was so contaminated with the original pad material, that three rounds of resurfacing couldn't clean them up. I did put my caliper on the two rotors and the Shimano is a little thicker (1.97mm to 1.83mm) so I don't know if that has anything to do with it.

One other thing: After a couple of bed-in runs, I was looking at the wear pattern on the new rotor. It didn't look like the pads were getting a full "bite" on the rotor, like the caliper was riding a little higher than it should be. I took out a cone washer from each mounting post and the caliper dropped about 2mm. Again, I could feel the braking power improve as a result. I guess it's just a matter of having a larger contact patch.

I'm hoping this is my last post on this issue and me and my Camber are going to live happily ever after. Thanks to all who offered advice!

 

[PuddleDuck]

Update: I'm hoping this is my last post on this issue and me and my Camber are going to live happily ever after. Thanks to all who offered advice!

Fingers crossed!

 

[DoctorJD]

I thought I'd give one final update on this saga. So after installing the new Shimano rotor and reinstalling the "cleaned" metallic pads, things never really improved. Power sucked and they still howled. So I bought a brand new pair of pads, and now I have braking nirvana. They operate the way XTs should operate.

So the pads were contaminated The mystery is: What was the source of the contamination?
The first two sets of Shimano metallics either, a) were contaminated somehow with the pad material from the Sram rotors or, b) the alcohol I was using was tainted.

Anyway, this episode is over, and I learned a valuable lesson: Don't be cheap, just by new pads.