My roadrat has now had 3 sets of disk brakes on it, they all loose power after a few weeks and sound like chewbacca chewing a wasp. The current set are XTs off my other bike, they were brilliant when I put them on and now its like the rotors are covered in silicon. I dont believe 3 sets of seals all failed once used for commuting, chain gets oil dripped on it and then towelled off so its not that- so maybe road film or original magura rotors are soft or something?

Ive cleaned the rotors with IPA which doesn’t really help.

Strangely they work really well when its raining and theres water on the pads / rotors.

Mine seem fine hope with sintered pads or bb7s

long term bb7 user here. they just keep working no matter what.

Road contamination coupled with light braking.

I used to experience this on a regular basis commuting through town. My cure was to make a weekly detour down a very steep hill and get the rotors really hot.

Sounds a bit funny. My commuter has really scuzzy Promax mechanical discs and I didn’t have high hope for them. They’ve done pretty well, about 2000km over the winter on salty roads and paths and still working absolutely fine and quitely with zero maintenance / cleaning other than pad adjustment. They’re not amazing but reasonable modulation and more than enough power to lock the wheels up.

Are the roads you’re riding on particularly oily / dirty / contaminated? Like through industrial estates or depots and the like?

Road contamination coupled with light braking.

I used to experience this on a regular basis commuting through town. My cure was to make a weekly detour down a very steep hill and get the rotors really hot

That sounds possible. I’ve got a couple of reasonable descents on my commute with traffic lights that involves some pretty hard breaking on a daily basis.

my BB7s used to yowl like crazy. Absolutely ridiculous when it was wet. I used to get regular comments at the lights “Why are your brakes so loud?” “What have you done to your brakes to make them so loud?” Are all disc brakes that loud?”

I used to use them as a safety feature for pedestrians – quick dab/yowl on a coupld of little back roads where people are prone to stepping out without looking.

Then got superstar organics and they’re very quiet most of the time, whisper of the pads on the vents, and bit of a murmur when it’s damp. Braking is just as good as the original avids, life maybe 50%, cost – 25%

Edit – none of that is relevant to your question, scruff, sorry for wasting everyone’s time!

Hmm, all normal roads and gravel paths. I can pretty much ride all the way in downhill without braking apart from dogs on extender leads and highly skilled immigrant engineering workers on the one usable cycle path.

And Ive tried Shimano resin, superstar sintered and kevlar.

Howling +

Strangely they work really well when its raining and theres water on the pads / rotors.

My XT’s did this too, when I first got them they were awesome, then didnt use the bike for a couple of weeks, next time out massive howling, checked seals, all fine’n’dandy.

Pads out, scrubbed, cleaned disks, still did it. Turned the garden hose on them and went for a big descent to re-bed them and back to normal… for about 10mins.

Finally relented, and put new pads in, been fine ever since.

I have no idea what actually happened to them as they can’t have been contaminated by anything while sitting there not doing anything, I put it down to some freak glazing/pads going off problem.

I can see how they might glaze over with only light braking, squeel with minor contamination but the working great when wet thing is weird.

BB5’s, for two years on same pads, 2 miles a day, no issue.

Deore hydro’s been using them for a few months commuting by road, 2 days a week 14 miles each way. Haven’t noticed any decrease in braking performance but I do have a few big hills (Chesterfield – Sheffield) that I use the brakes on.

The brakes are about 18 months old and I use UberBikes sintered pads.

Been running BB5s on my CX bike for 6 years now, never really had any squealing issues. I’ve had to replace both calipers, many sets of pads, and been running XTR rotors for past 2 years – hardly any squeal, apart from when they first get some moisture on the rotors, but that’s the same with all disc brakes.

You mention ‘glaze’ on the rotor. It’s normal for the brake pads to deposit material onto the rotor surface. The effectiveness of disc brakes is in fact the friction of the pad against the pad material embedded onto the rotor surface.

To really remove this ‘glaze’ you need to rub the rotors down with something like 200 grade emery paper, and then clean with IPA.

In your case, I’d check caliper alignment. Properly working calipers must be parallel to the rotor, otherwise the pad/rotor contact can experience a high frequency ‘juddering’ which we hear as a howling Wookie 😯