My Cannondale Jekyll came with Magura MT2 brakes and 185mm discs front and back when I bought it new. Trying to bed them in at home with sintered pads to get them to work, didn’t inspire riding confidence. Then a week in Spain using organic pads, was slightly unnerving, with the smells of burning brakes and blue discs. Maybe I should have MTFU and just ridden faster !! Back home, I decide to swop the brakes for a set of Zee’s using the same discs. I still cant stop. Tried emery cloth and cleaning the discs, different pads, still cant lock the front wheel when pushing alongside the bike. Can blued discs change the finish on the discs ? I have now ordered new 203mm front and 185mm discs, but just wondered if that is the reasoning of no brakes

The blue-ing is a sign the disc has been hot and that the chrystal structure of the material may have changed. That doesn’t mean that the co-efficient of friction has changed.

Since you’ve changed the brakes (that included pads – right?) it should all operate correctly.

I don’t understand the reason they’re not working.

Is there anything else you haven’t told us?

My zee’s were very disappointing at first but they just take a while to bed in.

Should have bought Hope brakes…. 😉

JAG + 1/2.

You likely got some odd oxides developing on the braking surface. The friction behaviour may change as a result of this. The cause of friction is a hotly debated topic in my field. Otherwise, if you’re really dragging the brakes and it’s a hot day, perhaps you’ve had some recrystallisation due to tempering of the surface regions. Depending on which friction camp you’re in, a change in mechanical behaviour of the top surface may be a sufficient explanation.

However, friction is a product of a material pair (e.g. brake disc surface and brake pad). Changing pads may adjust the coefficient of sliding friction, although it may not.

I would bet that the most important thing to do is to have the correct pad and disc roughness (formed after being bedded in) and to have a suitable tribolayer on the interacting surfaces. The friction behaviour is likely due to an interaction between the metal disc surface region, metal disc bulk, pad surface region, pad bulk region and a corresponding tribofilm formed due to an aggressive sliding contact.

I don’t expect that to be very helpful!

^ that’s what I was thinking

I had some problems out of my Saints when I got them. I was using my old shimano rotors that I thought were fine, but were actually lipped by 0.5mm either side. New rotors and it’s like hitting a wall of treacle.

In ref to the blue-ing / bronzing you describe. I did that to a 160mm rotor with resin pads in the alps. It was ruined and never braked the same again. Looked good though. 🙂

I don’t expect that to be very helpful!

Nail. Head.

Slightly more scientific that i was hoping !! Hope brakes ! Rather throw a stick in the front wheel. From my scientific perspective, they have never ‘really’ worked. i have changed pads from sintered to Kevlar to the white Uberbike ones. Nothing is grabbing at all. The only thing I havent changed are the discs. On a Swinley ride this weekend, they just got no heat in them at all and was interesting in some sections, where I gained more speed than I could loose. I also wonder on the discs having excessive cut outs/ holes in them, as that will lower the friction available, hence why I have bought and am waiting the solid Zee discs. I will photo the discs against the Zee’s and show the surface of the discs. Its almost like there is no friction on the disc, it just slides through ‘smoothly’, even though I have used heavy emery cloth to rough up and cleaned up. I wet the discs the other night and I think most of the county heard the howling. Massive noise and no stopping at all.
My deores on old Avids discs are just mental power on my C456, so was hoping for something on a similar line with these. Sadly I cant swop wheels to try, I would have to swop discs over, which is a faff. Centrelock adaptors etc.
Must admit they look good with blue spokes on the discs, but everyone in Spain wondering who was burning, as I shot through the middle of them, was a bit dodgy.

Have not had any particular issues with blued discs tbh. When I started doing a bit of recreational dh I was a serial brake dragger and used to fry the rear disc it was blue/straw/black sometimes. Generally wore off after few rides can’t say I noticed anything untoward

Layman’s guide to first year undergrad metallurgy

http://www.gowelding.com/met/carbon.htm

Before moving on to sexier materials 😉

Contaminated disc(s) maybe? I just binned a contaminated disc that had a blueish tinge. Might be worth changing pads again when you get the new rotors.

I have put the Maguras on my ride to work mtb tonight as found a fluid leak on the avids and cant be arsed with them any more. The Maguras were teamed up with the Hope discs that the avids were running on. All I can say, is the power of then is spot on. So this is pointing at the discs on the ‘dale being the issue. I will post a piccie when the Zee discs appear as a comparison.

I had a similar problem with older magura brakes which I bought second hand for my winter bike..was always thinking the problem are pads or caliper..tried everything …finally installed new discs ( cheap shimano ones) and everything is fine !!

I turn the TRP HyRd disc’s on my CX bike brown/blue on a regular basis, the disc warp a bit sometimes but they seem to straighten out again the next time they warm up.
There’s a video on youtube of TRP’s being tested to red hot multiple times in succession.

The cheap solid metal shimano ones (think they’re the SLX level ones) are really good. Just pick a set up and see how they go.

I’ve often had disc go blue, braking hasn’t been effected. Pads get very noisy when they are that hot though, HOOONNNNKKKKK!

Well, new discs are here and the front is more the size I need.
Just a 4 mile ride around is starting to get some friction and braking into the brakes at last.

Struggling to upload the old disc, will try later.

One of the 2 duffed discs…….