Black gunk on my disk rotor where does it come from?
10-09-21, 09:32 PM
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Black gunk on my disk rotor where does it come from?
I never had this issue till I got a new wheel set.This is on our tandem and its s a Shimano deore 4 piston caliper with metallic pads. I Have been getting black streaks on the rotor and the braking force is about halved or less. The picture shows a tiny bit I forgot to take the pic till I took the alcohol to it and rode while the pads were wet for a bit to clean them. it was pretty black streaky before I cleaned them. this happened about 300 miles ago and I had to sand it off. but the pads was worn so I thought that was the cause and replaced them. but now it is doing it again. the alcohol got most of it but I have no clue about why. could it be riding the brakes when we go down long steep hills? usually if I need to do it that I change from back to front so each rotor has a little time to cool or have my wife use the rim brake for a bit. the front is always clean. this is a Shimano ice tech 203 mm rotor. the new wheel set I had to go from center lock to a 6 bolt mount. As far as I know I have not gotten anything on the rotor.
10-10-21, 07:24 AM
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Bikes: 1980's Royce Union "fixed wheel", 1995 Trek 370, 406 -wheeled " shopper/minivelo"for running errands, SS Raleigh M60
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Looks like the pad(s) got contaminated from oil. Is the caliper leaking from the piston; have you lubed the chain in situ and have the lube sprayed onto the pads?
10-10-21, 08:20 AM
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no leaks on the caliper they feel fine andI have been lubing the chai the same ay the whole time I ahve had the bike and I never get it on the disc. we do go off-road a bit on the tandem on hard packed trails could it be the dust and the heat? I use rock and roll lube so it is nice and dry
10-10-21, 09:12 AM
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By looking again at the picture, the rotor's braking surface looks discolored; could it be that it's getting too hot? Maybe sand/true the rotor, sand pads and test?
10-10-21, 09:36 AM
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I am thinking heat too. this is a ice tech rotor so it should dissipate heat well but to sure. we had a crash early last year and the mechanic though the rotor had been overheated or something. it was a ice tech rotor too. so maybe going down steep grades at only 25mph may be overheating it.I try to change up what brake is getting used and if ti is long I will have my wife use the rim brake. so maybe I need to use the rim brake more on long decents? we are not brake anymore so we don't fly down hills we also have some very steep slopes like 20% grades that are short maybe those could create fast that and cool cycles causing issues? the discs are nice and true and the pads are fresh. when we had 180 discs and single piston calipers we would often have brake fade on long descents.
