casperrasper Posted September 25, 2013 Report Share Posted September 25, 2013 Gasgas pro 2013 ...recently boiled back brake had flames .so I changed seals and piston on caliper bled up using swringe got pressure on pedal but I can't get the wheel to lock up when riding .im thinking have I scraped the disc ..any body got any ideas what the problem may be ..... Quote Link to comment Share on other sites More sharing options...
mike_b Posted September 25, 2013 Report Share Posted September 25, 2013 Have you tried riding it round with your foot on the brake to get it hot again then chucking cold water on it? Worked for me, but sure someone will tell you it's bad for some reason. How on earth did you manage to set fire to it in the first place though...?! Quote Link to comment Share on other sites More sharing options...
zippy Posted September 25, 2013 Report Share Posted September 25, 2013 Try sanding the pads to remove any glaze try using some wet/dry a million something grit sandpaper on the disc, wetted with some WD-40 or similiar. then clean disc thouroughly with brake cleaner. Good luck. 1 Quote Link to comment Share on other sites More sharing options...
nelly1 Posted September 25, 2013 Report Share Posted September 25, 2013 Have you tried riding it round with your foot on the brake to get it hot again then chucking cold water on it? Worked for me, but sure someone will tell you it's bad for some reason. How on earth did you manage to set fire to it in the first place though...?! this usually works for me too Quote Link to comment Share on other sites More sharing options...
casperrasper Posted September 25, 2013 Author Report Share Posted September 25, 2013 Set on fire riding across a big field didn't have enough free play on pedal ...I have rode round brake on then watered disc that works fine for a few mins Quote Link to comment Share on other sites More sharing options...
wakka Posted September 25, 2013 Report Share Posted September 25, 2013 Replace the disc Rotor you have over heated the steel, it will never be any good good luck Quote Link to comment Share on other sites More sharing options...
copemech Posted September 26, 2013 Report Share Posted September 26, 2013 Steel is steel! If you have cooked the pads, chunk them and start over! Be sure you have clearance and full return of the MC piston. Quote Link to comment Share on other sites More sharing options...
charlie chitlins Posted September 26, 2013 Report Share Posted September 26, 2013 Cope's right again...or is it STILL right? Mild steel or cast iron, which most rotors are made of, can't be tempered, hardened, annealed, etc. because of its low carbon content....even if it does turn colors (oxides) like higher carbon tool steel. It also rusts quite easily...just look at the rotors on your car if it sits in damp weather for a couple days. This makes me unsure of what kind of steel trials bike disks are made of...they don't seem to rust. If there is carbon or nickel (as with stainless), they could be affected by heat. If anybody wants to send me an old one, I could heat it up and whack it around the anvil and give a report. There are also charts that show the pattern of sparks different metals make when put to a grinding wheel. Every one is different and old-time blacksmiths used to be able to put a piece of metal to a wheel and tell you what it was. Quote Link to comment Share on other sites More sharing options...
0007 Posted September 26, 2013 Report Share Posted September 26, 2013 Good info Charlie Also heating metal and letting it cool without quenching is what takes hardness out of steel Quenching with water in particular increases hardness Heating to 400 - 500f is all it takes to soften steel, not really all that hot Quote Link to comment Share on other sites More sharing options...
anotherfive Posted September 26, 2013 Report Share Posted September 26, 2013 I hope you used the old pads whilst bleeding the system. Using my old pads and the water trick also lasted me a few mins then oils come to surface again. new pads and bed in. More serious is a warped disc pushing the pads apart as disc passes through on each revolution. Quote Link to comment Share on other sites More sharing options...
sting32 Posted September 26, 2013 Report Share Posted September 26, 2013 make sure both sides pistons are moving, I had one stick, hardly any brake, then it made the rotor work screws out Quote Link to comment Share on other sites More sharing options...
casperrasper Posted September 26, 2013 Author Report Share Posted September 26, 2013 Both pistons move freely . Orderd a new disc should be here Saturday got a comp Sunday so I will post if it works good .. Thanks for all the info Quote Link to comment Share on other sites More sharing options...
guys Posted September 26, 2013 Report Share Posted September 26, 2013 Cope's right again...or is it STILL right? Mild steel or cast iron, which most rotors are made of, can't be tempered, hardened, annealed, etc. because of its low carbon content....even if it does turn colors (oxides) like higher carbon tool steel. It also rusts quite easily...just look at the rotors on your car if it sits in damp weather for a couple days. This makes me unsure of what kind of steel trials bike disks are made of...they don't seem to rust. If there is carbon or nickel (as with stainless), they could be affected by heat. If anybody wants to send me an old one, I could heat it up and whack it around the anvil and give a report. There are also charts that show the pattern of sparks different metals make when put to a grinding wheel. Every one is different and old-time blacksmiths used to be able to put a piece of metal to a wheel and tell you what it was. Most motorcycle disc rotors are stainless steel with a higher steel content because it's still magnetic. Cast iron is to brittle, specialy for off road bikes. The only bikes I can remember that had cast iron discs where old Moto Guzzi's. I drilled holes in the discs on my '98 315R and I can tell you that they where much harder than ordinary steel: I used a carbide drill for hardened steel which was blunt in no time. Quote Link to comment Share on other sites More sharing options...
charlie chitlins Posted September 30, 2013 Report Share Posted September 30, 2013 Stainless doesn't have a particularly good friction coefficient. When I had my repair shop (Harley related), a lot of folks wanted to switch to stainless rotors because form tends to trump function in that crowd. It was pretty shocking how poorly the stainless rotors worked compared to stock. Last I read (which was maybe 7 or 8 years ago), F1 was still using cast iron, but considering carbon fiber. Quote Link to comment Share on other sites More sharing options...
zippy Posted September 30, 2013 Report Share Posted September 30, 2013 It was pretty shocking how poorly the stainless rotors worked compared to stock. But they looked BAD ASS as they continued to roll into the intersection. 2 Quote Link to comment Share on other sites More sharing options...
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